61 results on '"Heng-Kwong Tsao"'
Search Results
2. Preferred penetration of active nano-rods into narrow channels and their clustering
- Author
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Heng Kwong Tsao, Zhengjia Wang, Yu Jane Sheng, and Kang Ching Chu
- Subjects
Work (thermodynamics) ,Materials science ,genetic structures ,Dissipative particle dynamics ,General Physics and Astronomy ,02 engineering and technology ,Penetration (firestop) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Molecular physics ,Power law ,Rod ,0104 chemical sciences ,Partition (number theory) ,sense organs ,Physical and Theoretical Chemistry ,0210 nano-technology ,Communication channel ,Entropic force - Abstract
In a channel connected to a reservoir, passive particles prefer staying in the reservoir than the channel due to the entropic effect, as the size of the particles is comparable to that of the channel. Self-propelled rods can exhibit out-of-equilibrium phenomena, and their partition behavior may differ from that of passive rods due to their persistent swimming ability. In this work, the distribution of active nano-rods between the nanoscale channel and reservoir is explored using dissipative particle dynamics. The ratio of the nano-rod concentration in the slit to that in the reservoir, defined as the partition ratio Ψ, is a function of active force, channel width, and rod length. Although passive nano-rods prefer staying in bulk (Ψ1), active rods can overcome the entropic barrier and show favorable partition toward narrow channels (Ψ1). As the slit width decreases to about the rod's width, active rods entering the slit behave like a quasi-two-dimensional system dynamically. At sufficiently high concentrations and Peclet numbers, nano-rods tend to align and move together in the same direction for a certain time. The distribution (PM) of the cluster size (M) follows a power law, PM ∝ M-2, for small clusters.
- Published
- 2021
3. Size-dependence and interfacial segregation in nanofilms and nanodroplets of homologous polymer blends
- Author
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Kang Ching Chu, Heng Kwong Tsao, Yu Jane Sheng, Yu Hao Tsao, and Wan Ju Liao
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chemistry.chemical_classification ,Materials science ,education ,Dissipative particle dynamics ,food and beverages ,General Physics and Astronomy ,02 engineering and technology ,Polymer ,021001 nanoscience & nanotechnology ,01 natural sciences ,Surface tension ,Contact angle ,symbols.namesake ,Gibbs isotherm ,chemistry ,Chemical physics ,0103 physical sciences ,symbols ,Polymer blend ,Wetting ,Physical and Theoretical Chemistry ,010306 general physics ,0210 nano-technology ,Size dependence - Abstract
The size-dependent behavior of nanofilms and nanodroplets of homologous polymer blends was explored by many-body dissipative particle dynamics. Although a homologous blend can be regarded as a completely miscible and athermal system, enrichment of the surface in short polymers always takes place. First, liquid–gas and solid–liquid interfacial tensions of polymer melts were acquired. It is found that they increase and approach asymptotes with increasing chain lengths. The molecular weight dependence can be depicted using two semi-empirical expressions. Second, the variation of surface tension and surface excess of polymer blend nanofilms with the thickness was observed. Surface tension of the blend is observed to increase but the extent of surface segregation decreases upon increasing the film thickness. Finally, the wetting phenomenon of nanodroplets of homologous blends was examined. The contact angle is found to increase as the droplet size is reduced. Our simulation results indicate that the size-dependence of nanofilms and nanodroplets is closely related to surface segregation in homologous blends.
- Published
- 2020
4. Branching pattern effect and co-assembly with lipids of amphiphilic Janus dendrimersomes
- Author
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Yu Jane Sheng, Heng Kwong Tsao, and Yan Ling Yang
- Subjects
Dendrimers ,Chemistry ,Bilayer ,Lipid Bilayers ,Dissipative particle dynamics ,Water ,General Physics and Astronomy ,02 engineering and technology ,Molecular Dynamics Simulation ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Branching (polymer chemistry) ,Lipids ,01 natural sciences ,0104 chemical sciences ,Molecular dynamics ,Membrane ,Dendrimer ,Amphiphile ,Biophysics ,Janus ,Physical and Theoretical Chemistry ,0210 nano-technology ,Hydrophobic and Hydrophilic Interactions - Abstract
The influence of the branching patterns on the membrane properties of Janus dendrimers in water has been investigated by dissipative particle dynamics simulations. The hydrophobic fluorinated dendron (RF) contains three types of branching patterns, including 3,4-, 3,5-, and 3,4,5-RF. Consistent with experimental results, the hydrophobic layer thickness (HB) follows the order: 3,5-RF3,4-RF3,4,5-RF, which can be explained by the extent of interdigitation (Δh): 3,5-RF3,4-RF3,4,5-RF. Moreover, the 3,4,5-RF membrane shows the highest stretching modulus (KA) and the lowest lateral diffusivity (D). The 3,5-RF membrane is similar to the 3,4-RF membrane but exhibits a higher KA and smaller D. For the nano-sized dendrimersome, its bilayer thickness is less than that of the planar membrane due to its larger extent of interdigitation. The co-assembly of dendrimersomes with lipids has been studied as well. The thickness and the extent of interdigitation of the lipid-rich domain for the hybrid membrane are significantly affected by the lipid concentration (φl) and the branching patterns. As φl increases, the thickness of the lipid-rich domain grows corresponding to the decrease of interdigitation of the lipid-rich domain.
- Published
- 2018
5. Amphibious superamphiphilic polystyrene monolith with underwater superoleophilicity: Capture of underwater oil
- Author
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Trung Hieu Vo, Phuc Khanh Lam, Heng Kwong Tsao, and Yu Jane Sheng
- Subjects
geography ,Materials science ,geography.geographical_feature_category ,General Physics and Astronomy ,Surfaces and Interfaces ,General Chemistry ,Decane ,Condensed Matter Physics ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,Polymerization ,chemistry ,Chemical engineering ,Oil droplet ,Emulsion ,Polystyrene ,Absorption (chemistry) ,Monolith ,Porosity - Abstract
Three-dimensional porous polystyrene monolith was fabricated by emulsion templating and it showed superamphiphilicity in the air by absorption of both water and oil droplets rapidly (within seconds). When as-prepared polystyrene monolith was immersed in water, similar behaviors were observed, demonstrating its amphibious superamphiphilicity. In underwater environment, the monolith can be easily filled with water which can be completely displaced by oil as contact with oil droplets, referred to as underwater superoleophilicity. Those interesting properties can be attributed to high porosity provided in emulsion templating and the hydrophilic and oleophilic domains which remain at the interface of interconnected pores after polymerization. The as-prepared monolith was able to absorb at least twenty types of solvents and the maximum uptake capacity was comparable to the performances of other polystyrene absorbents. Moreover, the absorbing capacity remained unchanged after 10 cycles of water and decane absorption and desorption, indicating its good reusability. With the high affinity toward oil, the monolith was able to remove oil spillage and organic pollutants from water and it can be used as an advanced absorbent for underwater oil capture.
- Published
- 2021
6. Spreading dynamics of a precursor film of nanodrops on total wetting surfaces
- Author
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Cyuan Jhang Wu, Yu Jane Sheng, Yu Hsuan Weng, and Heng Kwong Tsao
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Condensed matter physics ,Chemistry ,business.industry ,Dissipative particle dynamics ,General Physics and Astronomy ,Spherical cap ,02 engineering and technology ,Surface finish ,Radius ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Power law ,0104 chemical sciences ,Contact angle ,Optics ,Surface roughness ,Wetting ,Physical and Theoretical Chemistry ,0210 nano-technology ,business - Abstract
The spreading dynamics of a nanodrop on a total wetting surface is explored by many-body dissipative particle dynamics. Both smooth and rough surfaces with various spreading coefficients (S) are considered. The evolution of the spreading film is mainly characterized by the radius of the wetting area (Rp) and the apparent base radius (Rb) and the contact angle (θ) of the spherical cap. The difference between Rp and Rb reveals the presence of the precursor film. The dynamic behavior can be described by the power law: Rp ∼ tm, Rb ∼ tn, and θ ∼ t−α. Regardless of the surface roughness, the exponents n = 0.1 and α = 0.3 agree with Tanner's law and are independent of the spreading coefficient. However, the expansion of the precursor film depends on the surface roughness and the spreading coefficient. As the cavity size corresponding to the roughness decreases or S increases, the exponent m can rise approximately from 0.1 to 0.2. That is, the spontaneous expansion is driven by the spreading coefficient but impeded by the surface roughness. Forced spreading of a nanodrop on a smooth surface leads to anisotropic expansion. The length along the force direction L(t) follows the power law L ∝ tp and the exponent p ≈ 0.274 is insensitive to S. Nonetheless, the length along the direction perpendicular to the force direction is dominated by the spontaneous spreading. Contact line pinning of the rear end is only observed for intermediate forces.
- Published
- 2017
7. Water-repellent hydrophilic nanogrooves
- Author
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Yu Jane Sheng, I-Fan Hsieh, Yu-Hsuan Weng, and Heng Kwong Tsao
- Subjects
business.industry ,Chemistry ,Drop (liquid) ,Dissipative particle dynamics ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Contact angle ,Optics ,Water repellent ,Rough surface ,Surface roughness ,Imbibition ,Wetting ,Physical and Theoretical Chemistry ,Composite material ,0210 nano-technology ,business - Abstract
The wetting behavior of a nanodrop atop a nanogroove on a smooth or a rough surface is explored by many-body dissipative particle dynamics and Surface Evolver. The nanogroove possesses the same contact angle (θY) as that of the surface. Depending on whether the groove is initially wetted or not, two critical contact angles beyond which the groove cannot be wetted are determined. Three regimes are identified: (i) as θY ≤ θcY, the groove is always wetted; (ii) as , both impregnated and unwetted states can be observed; (iii) as , the groove cannot be impregnated. As the drop volume is increased, both θcY and decrease but become insensitive to the volume eventually. Surface roughness tends to hamper the impregnation of grooves by liquid. Compared to a smooth surface, both critical contact angles of a rough surface with regular shallow pits are smaller. As a result, a large drop is unable to wet the groove with a rough surface even when the surface becomes slightly hydrophilic. When the surface structure within the groove is modified from shallow pits to straight trenches, the critical contact angle is further reduced. Our simulation outcomes show that the surface structure within the groove is crucial for liquid imbibition and it is possible to fabricate hydrophilic cavities that can prevent impregnation, without resorting to chemical modification processes.
- Published
- 2017
8. Bilayered membranes of Janus dendrimers with hybrid hydrogenated and fluorinated dendrons: microstructures and coassembly with lipids
- Author
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Yu Jane Sheng, Yan Ling Yang, and Heng Kwong Tsao
- Subjects
Dendrimers ,Materials science ,Morphology (linguistics) ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Micelle ,Dendrimer ,Computer Simulation ,Fluorocarbon ,Janus ,Physical and Theoretical Chemistry ,Micelles ,Dissipative particle dynamics ,Membranes, Artificial ,Fluorine ,021001 nanoscience & nanotechnology ,Microstructure ,Lipids ,0104 chemical sciences ,Membrane ,Chemical engineering ,lipids (amino acids, peptides, and proteins) ,Hydrogenation ,0210 nano-technology - Abstract
A biomimetic membrane formed by hybrid Janus dendrimers (JDs) which contain hydrogenated and fluorinated dendrons was explored by dissipative particle dynamics simulations. The JD membrane is bilayered and shows a bicontinuous morphology which is also observed in nano-sized dendrimersomes. The thickness of the dendrimersome is significantly less than that of the planar membrane. The co-assembly of lipids with JDs to develop a hybrid membrane was studied as well. Lipids tend to locate in the hydrocarbon domain of the bicontinuous structure of the JD-rich membrane, while 2-dimensional micelles of JDs float in the leaflet of the lipid-rich membrane. The microstructure of the hybrid membrane was quantified by interdigitation lengths in the hydrocarbon, fluorocarbon, and lipid domains. Finally, the influence of lipid concentration on lipid fluidity was examined in terms of lipid diffusivity, which is found to be closely associated with the membrane microstructure.
- Published
- 2019
9. Contact Angle Hysteresis on Graphene Surfaces and Hysteresis-free Behavior on Oil-infused Graphite Surfaces
- Author
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Heng Kwong Tsao, Yu Jane Sheng, Yueh Feng Li, Wei Yen Woon, and Cyuan Jhang Wu
- Subjects
Materials science ,Graphene ,General Physics and Astronomy ,Nanotechnology ,02 engineering and technology ,Surfaces and Interfaces ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,law.invention ,Contact angle ,Hysteresis ,Wetting transition ,Highly oriented pyrolytic graphite ,law ,Graphite ,Wetting ,Composite material ,0210 nano-technology ,Graphene oxide paper - Abstract
Contact angle hysteresis (CAH) on graphitic surfaces, including chemical vapor deposition (CVD) graphene, reduced electrophoretic deposition (EPD) graphene, highly oriented pyrolytic graphite (HOPG), and polished graphite sheet, has been investigated. The hysteresis loops of water drops on the first three samples are similar but the receding contact angle is particularly small for the polished graphite sheet.The significant CAH observed on CVD graphene and HOPG associated with atom-scale roughness has to be attributed mainly to adhesion hysteresis (surface relaxation), instead of roughness or defects.The difference of the wetting behavior among those four graphitic samples has been further demonstrated by hexadecane drops. On the surface of HOPG or CVD graphene,the contact line expands continuously with time, indicating total wetting for which the contact angle does not exist and contact line pinning disappears. In contrast, on the surface of reduced EPD graphene, spontaneous spreading is halted by spikes on it and partial wetting with small contact angle (θ≈4°) is obtained. On the surface of polished graphite sheet, the superlipophilicity and porous structure are demonstrated by imbibition and capillary rise of hexadecane. Consequently, an oil-infused graphite surface can be fabricated and the ultralow CAH of water (∆θ≈2°) is achieved.
- Published
- 2016
10. Self-healing and dewetting dynamics of a polymer nanofilm on a smooth substrate: strategies for dewetting suppression
- Author
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Yu Jane Sheng, Heng Kwong Tsao, and Yu Hsuan Weng
- Subjects
chemistry.chemical_classification ,Materials science ,Spinodal decomposition ,Dissipative particle dynamics ,Nucleation ,General Physics and Astronomy ,02 engineering and technology ,Polymer ,Substrate (electronics) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,chemistry ,Chemical physics ,Metastability ,Wetting ,Dewetting ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
The self-healing and dewetting dynamics of a polymer nanofilm on a smooth, partial wetting surface are explored by many-body dissipative particle dynamics. Three types of dewetting phenomena are identified, (i) spinodal decomposition, (ii) nucleation and growth, and (iii) metastable self-healing. The outcome depends on the surface wettability (θY), the polymer film thickness (h0), and the radius of the dry hole (R0). The phase diagram of the dewetting mechanism as a function of θY and h0 is obtained for a specified R0. As the surface wettability decreases (increasing θY), the critical film thickness associated with the nucleation/self-healing crossover (hc) grows so that the metastability of the film can be retained by the self-healing process. In addition to θY and R0, hc depends on the polymer length (N) as well. It is found that a longer polymer requires a thicker nanofilm to avoid dewetting by nucleation. Two strategies for dewetting suppression are proposed. The metastability of a film of polymers with a large molecular weight can be promoted either by the addition of short polymers or by employing compact polymers such as star polymers. In the latter approach, the increment of the arm number enhances the nanofilm stability.
- Published
- 2018
11. Dynamics of bridge-loop transformation in a membrane with mixed monolayer/bilayer structures
- Author
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Heng Kwong Tsao, Yu Jane Sheng, Min Yi Chen, and Yan Ling Yang
- Subjects
chemistry.chemical_classification ,Materials science ,Membrane permeability ,Bilayer ,Relaxation (NMR) ,General Physics and Astronomy ,02 engineering and technology ,Polymer ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Thermal diffusivity ,01 natural sciences ,0104 chemical sciences ,Membrane ,chemistry ,Chemical physics ,Monolayer ,Copolymer ,Physical and Theoretical Chemistry ,0210 nano-technology - Abstract
Instead of forming a typical bilayer or monolayer membrane, both the bridge (I-shape) and loop (U-shape) conformations coexist in the planar membranes formed by ABA triblock copolymers in a selective solvent. The non-equilibrium and equilibrium relaxation dynamics of polymer conformations are monitored. The non-equilibrium relaxation time depends on the initial composition and increases with an increase in the immiscibility between A and B blocks. The equilibrium composition of the loop-shape polymer is independent of the initial composition and A-B immiscibility. However, the extent of equilibrium composition fluctuations subsides as the A and B blocks become highly incompatible. The influences of the A-B immiscibility on the geometrical, mechanical, and transport properties of the membrane have also been investigated. As the immiscibility increases, the overall membrane thickness and the B block layer thickness (h) increase because of the increment in the molecular packing density. As a result, both the stretching (KA) and bending (KB) moduli grow significantly with the increasing A-B immiscibility. Consistent with the case of typical membranes, the ratio KB/KAh2 = 2 × 10-3 is a constant. Although the lateral diffusivity of polymers is insensitive to immiscibility, the membrane permeability decreases substantially as the A-B immiscibility is increased.
- Published
- 2018
12. Facile manipulation of receding contact angles of a substrate by roughening and fluorination
- Author
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Yu Jane Sheng, Yueh Feng Li, Heng Kwong Tsao, and Cyuan Jhang Wu
- Subjects
Materials science ,General Physics and Astronomy ,Nanotechnology ,Surfaces and Interfaces ,General Chemistry ,Substrate (electronics) ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Contact angle ,chemistry.chemical_compound ,Hysteresis ,chemistry ,Surface roughness ,Polystyrene ,Wetting ,Composite material ,Methyl methacrylate ,Deposition (law) - Abstract
Contact angle hysteresis plays a paramount role in anti-smudge surfaces. In this study, surface roughness is systematically altered on some polymeric substrates such as polystyrene and poly(methyl methacrylate) by roughening and its effect on contact angle hysteresis is investigated via measuring advancing and receding contact angles of water. The wettability on these substrates is also modified by vapor-phase deposition of perfluorooctyltrichlorosilane, while the surface morphology is kept the same. As surface roughness is increased, the advancing contact angle grows but three types of the receding contact angle ( θ r ) behavior have been identified: (i) monotonic reduction of θ r , (ii) monotonic enhancement of θ r , and (iii) presence of a minimum of θ r . A plausible mechanism based on the stability of air pockets is proposed to explain our experimental findings. The manipulation of receding contact angles can be achieved based on our findings.
- Published
- 2015
13. Time-varying wetting behavior on copper wafer treated by wet-etching
- Author
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Shao Liang Cheng, Sheng Hung Tu, Chuan Chang Wu, Hsing Chen Wu, Heng Kwong Tsao, and Yu Jane Sheng
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Materials science ,Metallurgy ,technology, industry, and agriculture ,Oxide ,General Physics and Astronomy ,Wet cleaning ,chemistry.chemical_element ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Copper ,Surface energy ,Surfaces, Coatings and Films ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,Etching (microfabrication) ,Surface roughness ,Wafer ,Wetting - Abstract
The wet cleaning process in semiconductor fabrication often involves the immersion of the copper wafer into etching solutions and thereby its surface properties are significantly altered. The wetting behavior of a copper film deposited on silicon wafer is investigated after a short dip in various etching solutions. The etchants include glacial acetic acid and dilute solutions of nitric acid, hydrofluoric acid, and tetramethylammonium hydroxide. It was found that in most cases a thin oxide layer still remains on the surface of as-received Cu wafers when they are subject to etching treatments. However, a pure Cu wafer can be obtained by the glacial acetic acid treatment and its water contact angle (CA) is about 45°. As the pure Cu wafer is placed in the ambient condition, the oxide thickness grows rapidly to the range of 10–20 A within 3 h and the CA on the hydrophilic surface also rises. In the vacuum, it is surprising to find that the CA and surface roughness of the pure Cu wafer can grow significantly. These interesting results may be attributed to the rearrangement of surface Cu atoms to reduce the surface free energy.
- Published
- 2015
14. Directed drift and fluid pumping of nanoswimmers by periodic rectification-diffusion
- Author
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Yen-Fu Chen, Hsuan-Yi Chen, Heng Kwong Tsao, and Yu Jane Sheng
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Chemistry ,Diffusion ,Dissipative particle dynamics ,Ratchet ,General Physics and Astronomy ,02 engineering and technology ,Mechanics ,021001 nanoscience & nanotechnology ,01 natural sciences ,Classical mechanics ,Rectification ,Flow velocity ,0103 physical sciences ,Fluid dynamics ,Knudsen number ,Physical and Theoretical Chemistry ,Current (fluid) ,010306 general physics ,0210 nano-technology - Abstract
The steady ratchet transport of run-and-tumble nanoswimmers in a 3D microfluidic channel constructed by periodic chambers separated by half-cylinder funnels is explored by dissipative particle dynamics. Two regions in a chamber are identified: rectification and active diffusion. While the concentration gradient is driven by the concentration jump in the rectification region, the ratchet current is dominated by the diffusion rate in the active diffusion region, which is classified into normal and Knudsen types. The former obeys Fick's law and is proportional to va2τ, where va is the self-propulsion velocity and τ the run time. In addition, autonomous pumping of fluids is induced by aligned force dipoles associated with nanoswimmers accumulated near funnels, similar to the mechanism of bacteria carpet. The direction of fluid flow is the same as that of the ratchet current but the former is one order of magnitude smaller than the latter. Thus, the fluid velocity depends on the characteristics of nanoswimmers.
- Published
- 2017
15. Particle size-induced transition between surface segregation and bulk aggregation in a thin film of athermal polymer-nanoparticle blends
- Author
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Yu Jane Sheng, Heng Kwong Tsao, and Chih Yu Teng
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Materials science ,Nanocomposite ,Dissipative particle dynamics ,Polymer nanoparticle ,General Physics and Astronomy ,Nanoparticle ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Condensed Matter::Soft Condensed Matter ,Chemical physics ,Volume fraction ,Particle size ,Physical and Theoretical Chemistry ,Thin film ,0210 nano-technology ,Entropic force - Abstract
Surface segregation and bulk aggregation in a thin film of athermal polymer-nanoparticle blends have been investigated by dissipative particle dynamics simulations. The thin film is confined between two athermal walls and the shape of the nanoparticles is spherical or cubic. Both phases are driven purely by the entropic effect, i.e., depletion attraction, which depends significantly on the nanoparticle size. At a specified particle volume fraction, surface segregation dominates for small nanoparticles but bulk aggregation emerges for large ones. The transition between the two phases is a result of the competition between particle-wall and particle-particle depletion attractions. The dominance of the former leads to surface segregation while the control of the latter results in bulk aggregation. Since nanocubes possess more contact areas and thus exhibit stronger depletion attractions than nanospheres do, the crossover from surface segregation to bulk aggregation occurs at smaller particle size for nanocubes.
- Published
- 2017
16. Growing hydrophobicity on a smooth copper oxide thin film at room temperature and reversible wettability transition
- Author
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Sheng Hung Tu, Yu Jane Sheng, Shao Liang Cheng, Cyuan Jhang Wu, Hsing Chen Wu, and Heng Kwong Tsao
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Copper oxide ,Materials science ,General Physics and Astronomy ,chemistry.chemical_element ,Nanotechnology ,Surfaces and Interfaces ,General Chemistry ,Condensed Matter Physics ,Copper ,Surfaces, Coatings and Films ,Contact angle ,chemistry.chemical_compound ,Chemical engineering ,X-ray photoelectron spectroscopy ,chemistry ,Superhydrophilicity ,Wetting ,Thin film ,Layer (electronics) - Abstract
The thin CuO film is acquired by a quick dip of copper in H 2 O 2 solutions at room temperature. The CuO film appears smooth and exhibits superhydrophilic nature. The composition change cannot be verified by X-ray photoelectron spectroscopy but can be manifested by the water contact angle. In the ambient condition, the thickness of the oxidized layer and the surface hydrophobicity grow gradually, while the chemical composition of the overall oxidized film remains essentially unchanged. In the vacuum, the growth rate of the hydrophobicity is significantly elevated, revealing deoxidation on the upmost surface. Our results indicate that growing hydrophobicity on the CuO film is spontaneous and the reversible wettability transition can be observed by H 2 O 2 oxidation and vacuum deoxidation.
- Published
- 2014
17. Dynamic and mechanical properties of supported lipid bilayers
- Author
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Hsing Lun Wu, Heng Kwong Tsao, and Yu Jane Sheng
- Subjects
Lipid Bilayers ,General Physics and Astronomy ,02 engineering and technology ,Bending ,Molecular Dynamics Simulation ,010402 general chemistry ,Thermal diffusivity ,01 natural sciences ,Quantitative Biology::Subcellular Processes ,Diffusion ,Phase (matter) ,Transition Temperature ,Physical and Theoretical Chemistry ,Lipid bilayer ,Mechanical Phenomena ,Quantitative Biology::Biomolecules ,Flexural modulus ,Chemistry ,Bilayer ,Dissipative particle dynamics ,Lipid bilayer mechanics ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Condensed Matter::Soft Condensed Matter ,Crystallography ,Chemical physics ,Phosphatidylcholines ,0210 nano-technology - Abstract
Supported lipid bilayers (SLBs) offer an excellent model system for investigating the physico-chemical properties of the cell membrane. In this work, dynamic and mechanical properties of SLBs are explored by dissipative particle dynamics simulations for lipids with different architectures (chain length, kink, and asymmetry associated with lipid tails). It is found that the lateral diffusivity (Dx) and flip-flop rate (FF) grow with increasing temperature in both gel and liquid phases and can be described by an Arrhenius-like expression. Three regimes can be clearly identified for symmetric and asymmetric saturated lipids but only two regimes are observed for kinked lipids. Both Dx and FF grow with decreasing tail length and increasing number of kinks. The stretching (KA) and apparent bending (KB) moduli exhibit concave upward curves with temperature and the minima are attained at Tm. In general, the minima of KA and KB decrease with the chain length and increase with number of kinks. The typical relation among the bending modulus, area stretching modulus, and bilayer thickness is still followed, KB = βKAh(2) and β is much smaller in the gel phase. The dynamic and mechanical properties of lipids with asymmetric tails are found to situate between their symmetric counterparts.
- Published
- 2016
18. Partition thermodynamics of ionic surfactants between phosphatidylcholine vesicle and water phases
- Author
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Shun Cheng Wang, Chia Hui Hung, Shin Chi Chu, and Heng Kwong Tsao
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chemistry.chemical_classification ,Conductometry ,Chemistry ,Bilayer ,Aqueous two-phase system ,General Physics and Astronomy ,Interaction energy ,Partition coefficient ,chemistry.chemical_compound ,Phosphatidylcholine ,Physical chemistry ,Organic chemistry ,lipids (amino acids, peptides, and proteins) ,Physical and Theoretical Chemistry ,Lipid bilayer ,Alkyl - Abstract
The partition of ionic surfactants (sodium alkyl sulfate and alkyl trimethyl ammonium bromide) between phosphatidylcholine vesicles and aqueous phase is investigated by simple conductometry under different temperatures. The experimental results can be well represented by the proposed regular solution theory and the thermodynamic parameters satisfy the thermodynamic consistency. The deviation from ideal partition is manifested through the effective interaction energy between lipid and surfactant wb, which is O(kT) large. It is found that wb rises as the alkyl chain is decreased for a specified head group. This is attributed to significant mismatch of chain lengths between surfactant and lipid molecules. The partition coefficient K declines with increasing temperature. The energy barrier from bilayer to aqueous phase, Δμ/kT∝ln K, is in the range of 16–26 kJ/mol. As the alkyl chain length is decreased for a given head group, Δμ is lowered by 1.3–1.5 kJ/mol per methylene group. Two independent analyses are em...
- Published
- 2003
19. Interfacial tension of a salty droplet: Monte Carlo study
- Author
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Ching Hung Ho, Yu Jane Sheng, and Heng Kwong Tsao
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Chemistry ,Monte Carlo method ,General Physics and Astronomy ,Thermodynamics ,Electrolyte ,Electrostatics ,Surface tension ,Spherical model ,Strong electrolyte ,symbols.namesake ,Adsorption ,Gibbs isotherm ,symbols ,Physical and Theoretical Chemistry - Abstract
The interfacial tension of an aqueous droplet with 1:1 strong electrolytes is investigated by Monte Carlo (MC) simulations. The electrostatic interactions among ions are calculated directly by solving the Poisson equation based on the restricted primitive model. The surface excess and chemical potential are evaluated from MC. The latter can be reasonably described by the mean spherical model. The interfacial tension is then obtained through Gibbs adsorption isotherm. The addition of a strong electrolyte leads to the increase of the interfacial tension and the MC result accounts reasonably well for the observed interfacial tensions up to relatively high salt concentrations (∼1.0 M). For very dilute solutions, our results agree with the Onsager–Samaras (OS) limiting law. However, the OS theory underestimates the surface excess and the interfacial tension for high salt concentrations. It is found that hydration around ions plays a very important role in interfacial tension increment.
- Published
- 2003
20. Effect of the intermediate state on the loop-to-coil transition of a telechelic chain
- Author
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Heng Kwong Tsao, Jeff Z. Y. Chen, Yu Jane Sheng, and Han Jou Lin
- Subjects
Loop (topology) ,Crystallography ,Reaction rate constant ,Chain (algebraic topology) ,Chemistry ,Electromagnetic coil ,Binding energy ,Monte Carlo method ,General Physics and Astronomy ,Intermediate state ,Thermodynamics ,State (functional analysis) ,Physical and Theoretical Chemistry - Abstract
The kinetics of conformational fluctuations of a telechelic chain with two binding sites at both ends is studied by Monte Carlo simulations. The site-to-site binding energy is −e. An example of the telechelic biopolymer is RNA or ssDNA made of a homogeneous sequence such as poly(T) with complementary bases at both ends. The conformation of such a chain fluctuate from loop (closed) to coil (open) state and the probability of the coil state depends on the temperature. An all-or-none transition between open and closed states is often adopted to depict the melting curves. It is found that the two-state model fails due to the existence of the intermediate state. A three-state model including open, intermediate, and closed states is proposed. The melting curves obtained from such a scenario agree quite well with the simulation results and there are two characteristic temperatures. The rate constants from closed to intermediate states kc,i and from intermediate to open states ki,o are independent of chain length...
- Published
- 2003
21. Dipole moment of a microdroplet containing a macroion
- Author
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Ching Hung Ho, Heng Kwong Tsao, Yu Jane Sheng, and Chin Yao Tseng
- Subjects
chemistry.chemical_classification ,Quantitative Biology::Biomolecules ,Monte Carlo method ,General Physics and Astronomy ,Electrostatics ,Molecular physics ,Ion ,Condensed Matter::Soft Condensed Matter ,Dipole ,Classical mechanics ,chemistry ,Moment (physics) ,Physical and Theoretical Chemistry ,Counterion ,Poisson's equation ,Neutral particle - Abstract
The influence of a macroion contained in a microdroplet on the mean square dipole moment 〈p2〉, which manifests counterion fluctuation and correlation, is investigated through Monte Carlo (MC) simulations. This system models the protein-filled water-in-oil microemulsion droplet. The electrostatic interactions among ions are calculated directly by solving the Poisson equation based on the primitive model. 〈p2〉 obtained from MC is much larger than that calculated by solving the Poisson–Boltzmann equation. The probability of the macroion location is determined and the average macroion location 〈rp〉 is always off-center. In comparison with 〈rp〉 of a hard sphere in a microdroplet without counterions, the neutral particle is repelled from the interface due to electrostatic repulsions among ions. When the interface and the macroion possess charges of similar sign, the macroion is pushed further away from the interface. 〈p2〉 is a function of counterion concentration, macroion size, and macroion charge Zp. When the...
- Published
- 2003
22. Rate of diffusion-limited reactions for a fractal aggregate of reactive spheres
- Author
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Chin Yao Tseng and Heng Kwong Tsao
- Subjects
Reaction rate ,Fractal ,Chemistry ,Fractal derivative ,Reaction–diffusion system ,General Physics and Astronomy ,Thermodynamics ,SPHERES ,Physical and Theoretical Chemistry ,Multipole expansion ,Scaling ,Fractal dimension - Abstract
We study the reaction rate for a fractal cluster of perfectly absorbing, stationary spherical sinks in a medium containing a mobile reactant. The effectiveness factor η, which is defined as the ratio of the total reaction rate of the cluster to that without diffusional interactions, is calculated. The scaling behavior of η is derived for arbitrary fractal dimension based on the Kirkwood–Riseman approximation. The asymptotic as well as the finite size scaling of η are confirmed numerically by the method of multipole expansion, which has been proven to be an excellent approximation. The fractal assembly is made of N spheres with its dimension varying from D 1, η∼(ln N)−1 for D=1, and η∼N0 for D 1 the screening effect of diffusive interactions grows with the size, for D
- Published
- 2002
23. Overall rate constants for diffusion and incorporation in clusters of spheres
- Author
-
Yi Ming Yen, Shih-Yuan Lu, Chin Yao Tseng, and Heng Kwong Tsao
- Subjects
Physics ,Drag coefficient ,Dipole ,Moment (physics) ,General Physics and Astronomy ,Boundary (topology) ,SPHERES ,Statistical physics ,Physical and Theoretical Chemistry ,Diffusion (business) ,Multipole expansion ,Brownian motion - Abstract
Three numerical schemes and one approximate model are developed to compute the overall rate constants for diffusion and incorporation of small entities in clusters of spheres. These include the Brownian dynamic simulation, multipole expansion, boundary collocation, and a model linking diffusion-limited (DL) and nondiffusion-limited (NDL) data. The Brownian dynamic simulation is speeded up with a first-passage technique and is capable of taking the finite surface incorporation rate into account. The multipole expansion truncated at the dipole moment gives an excellent approximation while the second order boundary collocation is satisfactorily accurate. The DL to NDL model offers a quick and reasonably accurate estimate of the rate constant. Clusters of Euclidean dimensions, including 1D strings, 2D squares, and 3D cubes, are particularly investigated. The screening effect arising from the long range nature of the disturbance concentration field is found responsible for the variation in the overall rate constant due to structural variation in clusters, and becomes less pronounced as P increases. Here, P measures the relative dominance of surface incorporation over the diffusion. Also, the rate constants for the Euclidean clusters are found to obey the similar scaling laws as those confirmed by Tseng et al. [Phys. Rev. Lett. 86, 5494 (2001)] for the translational drag coefficient of clusters of spheres in the low Reynolds number flow regime.
- Published
- 2002
24. The mobility and diffusivity of a knotted polymer: Topological deformation effect
- Author
-
Yu Jane Sheng and Heng Kwong Tsao
- Subjects
chemistry.chemical_classification ,Solid-state physics ,Crossing number (knot theory) ,Monte Carlo method ,General Physics and Astronomy ,Thermodynamics ,Polymer ,Thermal diffusivity ,Topology ,Deformation effect ,Internal friction ,chemistry ,Physical and Theoretical Chemistry ,Scaling - Abstract
The effect of topological deformation on the mobility and diffusivity of a polymer chain in a good solvent is investigated by off-lattice dynamic Monte Carlo simulations. The topological deformation of the polymer is expressed through the knotted structure. The Nernst–Einstein relation is obeyed and thus the diffusivity is proportional to the mobility. As the crossing number of the knotted polymer, which characterizes the extent of the deformation, is increased, the mobility declines. A scaling analysis confirmed by simulations indicates that the deformation yields an extra contribution to the resistance ζN associated with a linear chain, αN−3/5p8/5, where N is the chain length and p is the length-to-diameter ratio associated with a maximum inflated knot. The mobility of the polymer chain is further reduced due to the confinement in a cylindrical tube. Nevertheless, the confinement only slightly increases the friction coefficients ζ and the internal friction constant α. Our numerical results for the Rouse...
- Published
- 2002
25. Phase behaviors and membrane properties of model liposomes: temperature effect
- Author
-
Heng Kwong Tsao, Yu Jane Sheng, and Hsing Lun Wu
- Subjects
Physics::Biological Physics ,Phase transition ,Liposome ,Chemistry ,Vesicle ,Dissipative particle dynamics ,Lipid Bilayers ,Temperature ,General Physics and Astronomy ,Elasticity ,Permeability ,Phase Transition ,Condensed Matter::Soft Condensed Matter ,Quantitative Biology::Subcellular Processes ,Crystallography ,Membrane ,Chemical physics ,Phase (matter) ,Marsileaceae ,Liposomes ,Computer Simulation ,Lipid bilayer phase behavior ,Physical and Theoretical Chemistry ,Lipid bilayer ,Gels - Abstract
The phase behaviors and membrane properties of small unilamellar vesicles have been explored at different temperatures by dissipative particle dynamics simulations. The vesicles spontaneously formed by model lipids exhibit pre-transition from gel to ripple phase and main transition from ripple to liquid phase. The vesicle shape exhibits the faceted feature at low temperature, becomes more sphere-like with increasing temperature, but loses its sphericity at high temperature. As the temperature rises, the vesicle size grows but the membrane thickness declines. The main transition (Tm) can be identified by the inflection point. The membrane structural characteristics are analyzed. The inner and outer leaflets are asymmetric. The length of the lipid tail and area density of the lipid head in both leaflets decrease with increasing temperature. However, the mean lipid volume grows at low temperature but declines at high temperature. The membrane mechanical properties are also investigated. The water permeability grows exponentially with increasing T but the membrane tension peaks at Tm. Both the bending and stretching moduli have their minima near Tm. Those results are consistent with the experimental observations, indicating that the main signatures associated with phase transition are clearly observed in small unilamellar vesicles.
- Published
- 2014
26. The interactions between ionic surfactants and phosphatidylcholine vesicles: Conductometry
- Author
-
Wen Liang Tseng and Heng Kwong Tsao
- Subjects
Conductometry ,Chemistry ,Bilayer ,Vesicle ,Analytical chemistry ,General Physics and Astronomy ,Micelle ,Partition coefficient ,chemistry.chemical_compound ,Phosphatidylcholine ,Critical micelle concentration ,Organic chemistry ,Physical and Theoretical Chemistry ,Lipid bilayer - Abstract
The interaction between ionic surfactants and phosphatidylcholine vesicles, which are prepared without addition of buffer and salt, is investigated by conductivity measurements. On the basis of the vesicle acting as a trap of charge carriers, the bilayer/aqueous phase partition coefficient K and the surfactant/lipid molar ratio Re of nine surfactants are determined. The thermodynamic consistency is satisfied by the measured parameters. The effects of the alkyl chain length (C10–C16) and ionic head group are then studied. The inverse partition coefficient K−1 is linearly related to the critical micelle concentration. The solubilizing ability Reb is a consequence of the competition between the surfactant incorporation into the bilayer and the formation of micelles. Consequently, the K parameter rises whereas the Reb parameter declines as the chain length is increased. The influence due to addition of salt is also discussed.
- Published
- 2001
27. Rate of diffusion-limited reactions in a cluster of spherical sinks
- Author
-
Heng Kwong Tsao, Shin Yuan Lu, and Chin Yao Tseng
- Subjects
Reaction rate ,Dipole ,Reaction rate constant ,Screening effect ,Computational chemistry ,Chemistry ,Cluster (physics) ,General Physics and Astronomy ,SPHERES ,Rate equation ,Physical and Theoretical Chemistry ,Multipole expansion ,Computational physics - Abstract
The reaction rate is calculated for a cluster of perfectly absorbing, stationary spherical sinks in a medium containing a mobile reactant. The diffusive interactions are accurately taken into account by employing the first-passage technique. The configurations of the clusters include three spheres, four spheres, regular polygons, linear chains, squares, and finite cubic arrays. For a given number of sinks, the reaction rate is decreased with increasing the compactness of the structure due to the screening effect. For a specified configurations, the asymptotic expressions for the reaction rate varying with the number of sinks are confirmed. By comparing results with these “exact” data, the method of multipole expansions up to the dipole level, which is suitable for a finite system of many sinks, proved to be an excellent approximation.
- Published
- 2001
28. Diffusion into a pair of reactive spheres with first-order reaction
- Author
-
Heng Kwong Tsao
- Subjects
Reaction rate ,Reaction rate constant ,Exact solutions in general relativity ,Chemistry ,First-order reaction ,Quadrupole ,General Physics and Astronomy ,Thermodynamics ,SPHERES ,Rate equation ,Mechanics ,Physical and Theoretical Chemistry ,Multipole expansion - Abstract
Exact series solutions for the reaction rates of two identical spherical sinks immersed in an infinite medium are presented for both reactant-impenetrable and -penetrable particles based on the method of twin spherical expansion. The reaction rates are explicitly expressed in terms of the interparticle distance from reaction- to diffusion-limited conditions. The effect of the ratio of the diffusivities inside and outside the sink is investigated. The existence of the second particle influences the reaction rate most substantially for the external diffusion-limited condition. The exact solutions are used to evaluate the accuracy of simple, analytical approximations obtained by including the first few multipole contributions only. The result by keeping terms up to quadrupole level gives values in excellent agreement with the exact solution.
- Published
- 2001
29. The degree of dissociation of ionic surfactant shells within a W/O microdroplet
- Author
-
Yu Jane Sheng, Heng Kwong Tsao, and C. Y. David Lu
- Subjects
chemistry.chemical_classification ,Aqueous solution ,General Physics and Astronomy ,Ionic bonding ,Dissociation (chemistry) ,Ion ,Gibbs free energy ,Condensed Matter::Soft Condensed Matter ,Physics::Fluid Dynamics ,symbols.namesake ,chemistry ,Chemical physics ,Computational chemistry ,Physics::Atomic and Molecular Clusters ,symbols ,Microemulsion ,Physics::Chemical Physics ,Physical and Theoretical Chemistry ,Counterion ,Neutral particle - Abstract
The degree of dissociation of ionic surfactant shells within a W/O microdroplet is investigated on the basis of the Poisson–Boltzmann equation and locally ideal mixing assumption. The degree of dissociation is the result of the competition between the entropy associated with counterions in the aqueous core and mixing of surfactant ions with associated surfactants on the shell, and the electrostatic energy. The degree of dissociation is found to depend on the geometry and is in the order: Two planar surfaces>cylinder>sphere of the same size. Moreover, for the same geometry, the degree of dissociation increases with the size of the droplet. The free energy change associated with a droplet due to dissociation is obtained. The effect of the solubilization of a neutral particle on the degree of dissociation is also studied. The solubilization is found to hinder the dissociation.
- Published
- 2000
30. Superhydrophilic graphite surfaces and water-dispersible graphite colloids by electrochemical exfoliation
- Author
-
Shih Ming Chen, Yueh Feng Li, Heng Kwong Tsao, Yu Jane Sheng, and Wei Hao Lai
- Subjects
Electrolysis ,Materials science ,Scanning electron microscope ,Analytical chemistry ,General Physics and Astronomy ,Graphite oxide ,Exfoliation joint ,Anode ,law.invention ,Contact angle ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,law ,Partial oxidation ,Graphite ,Physical and Theoretical Chemistry - Abstract
Superhydrophilic graphite surfaces and water-dispersible graphite colloids are obtained by electrochemical exfoliation with hydrophobic graphite electrodes. Such counterintuitive characteristics are caused by partial oxidation and investigated by examining both graphite electrodes and exfoliated particles after electrolysis. The extent of surface oxidation can be explored through contact angle measurement, scanning electron microscope, electrical sheet resistance, x-ray photoelectron spectroscopy, zeta-potential analyzer, thermogravimetric analysis, UV-visible, and Raman spectroscopy. The degree of wettability of the graphite anode can be altered by the electrolytic current and time. The water contact angle declines generally with increasing the electrolytic current or time. After a sufficient time, the graphite anode becomes superhydrophilic and its hydrophobicity can be recovered by peeling with adhesive tape. This consequence reveals that the anodic graphite is oxidized by oxygen bubbles but the oxidation just occurs at the outer layers of the graphite sheet. Moreover, the characteristics of oxidation revealed by UV peak shift, peak ratio between D and G bands, and negative zeta-potential indicate the presence of graphite oxide on the outer shell of the exfoliated colloids. However, thermogravimetric analysis for the extent of decomposition of oxygen functional groups verifies that the amount of oxygen groups is significantly less than that of graphite oxide prepared via Hummer method. The structure of this partially oxidized graphite may consist of a graphite core covered with an oxidized shell. The properties of the exfoliated colloids are also influenced by pH of the electrolytic solution. As pH is increased, the extent of oxidation descends and the thickness of oxidized shell decreases. Those results reveal that the degree of oxidation of exfoliated nanoparticles can be manipulated simply by controlling pH.
- Published
- 2013
31. Resisting and pinning of a nanodrop by trenches on a hysteresis-free surface
- Author
-
Cheng Chung Chang, Cyuan Jhang Wu, Heng Kwong Tsao, and Yu Jane Sheng
- Subjects
Materials science ,Condensed matter physics ,business.industry ,Drop (liquid) ,Dissipative particle dynamics ,General Physics and Astronomy ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Contact angle ,Optics ,Free surface ,Trench ,Surface roughness ,Wetting ,Physical and Theoretical Chemistry ,0210 nano-technology ,Contact area ,business - Abstract
The encounter of a nanodrop with a trench on a hysteresis-free surface is explored by many-body dissipative particle dynamics to show the effect of surface roughness on droplet wetting. A free nanodrop exhibits Brownian motion and the diffusivity decays exponentially with the liquid-solid contact area. In contrast, as the nanodrop sits on a trench, its random motion is constrained. Work must be done to overcome the energy barriers for the transition between free and trapped states. The potential energy landscape is thus constructed based on the force-displacement plot. It is shown that the trench acts as a hydrophobic blemish for capture but like a hydrophilic blemish for escape. A drop always breaks up after detachment from a hydrophilic trench. Therefore, the drop tends to bypass a small trench when it meets one. The macroscopic experiments are performed by fabricating liquid-infused surfaces with extremely low contact angle hysteresis. The experimental observations agree qualitatively with simulation outcomes.
- Published
- 2016
32. Wet nanogranular materials: colloidal glass and gel
- Author
-
Yu Jane Sheng, Heng Kwong Tsao, Yueh Feng Li, and Chia Nan Yuan
- Subjects
Chemistry ,General Physics and Astronomy ,Nanoparticle ,Nanotechnology ,Granular material ,symbols.namesake ,Colloid ,Pulmonary surfactant ,Chemical engineering ,symbols ,Particle size ,Wetting ,Physical and Theoretical Chemistry ,van der Waals force ,Porous medium - Abstract
Partially wet granular medium is a mouldable material due to capillary cohesion and its behavior plays key roles in geophysics. However, completely wet nanogranules may also demonstrate mouldable properties via van der Waals attraction and they exhibit colloidal glass or gel characteristics, depending on the solvent. As solvent-enhanced attractions prevail, phase separation is observed and nanogranular gel can be obtained. In contrast, as cage effects dominate, the stable slurry is seen and the nanogranular glass can be prepared. Upon surfactant addition, however, the arrested glass state changes into colloidal gel due to the formation of hydrogen bonds between nanogranules.
- Published
- 2011
33. Solubilization mechanism of vesicles by surfactants: effect of hydrophobicity
- Author
-
Heng Kwong Tsao, Yu Jane Sheng, Geng-Pei Chang, and Chun-Min Lin
- Subjects
Models, Molecular ,Chemistry ,Vesicle ,Dissipative particle dynamics ,General Physics and Astronomy ,Micelle ,Colloid ,Surface-Active Agents ,Pulmonary surfactant ,Chemical engineering ,Models, Chemical ,Solubility ,Solubilization ,Organic chemistry ,Computer Simulation ,Physical and Theoretical Chemistry ,Lipid bilayer ,Hydrophobic and Hydrophilic Interactions ,Micelles - Abstract
Simulations based on dissipative particle dynamics are performed to investigate the solubilization mechanism of vesicles by surfactants. Surfactants tend to partition themselves between vesicle and the bulk solution. It is found that only surfactants with suitable hydrophobicity are able to solubilize vesicles by forming small mixed micelles. Surfactants with inadequate hydrophobicity tend to stay in the bulk solution and only a few of them enter into the vesicle. Consequently, the vesicle structure remains intact for all surfactant concentrations studied. On the contrary, surfactants with excessive hydrophobicity are inclined to incorporate with the vesicle and thus the vesicle size continues to grow as the surfactant concentration increases. Instead of forming discrete mixed micelles, lipid and surfactant are associated into large aggregates taking the shapes of cylinders, donuts, bilayers, etc. For addition of surfactant with moderate hydrophobicity, perforated vesicles are observed before the formation of mixed micelles and thus the solubilization mechanism is more intricate than the well-known three-stage hypothesis. As the apparent critical micellar concentration (φ(s,v)(a,CMC)) is attained, pure surfactant micelles form and the vesicle deforms because the distribution of surfactant within the bilayer is no longer uniform. When the surfactant concentration reaches φ(s,v)(p), the vesicle perforates. The extent of perforation grows with increasing surfactant concentration. The solubilization process begins at φ(s,v) (sol), and lipids leave the vesicle and join surfactant micelles to form mixed micelles. Eventually, total collapse of the vesicle is observed. In general, one has φ(s,v)(a,CMC)≤φ(s,v)(p)≤φ(s,v)(sol).
- Published
- 2011
34. Velocity distribution functions for a bidisperse, sedimenting particle-gas suspension
- Author
-
Heng Kwong Tsao, Donald L. Koch, and Vinay Kumaran
- Subjects
Fluid Flow and Transfer Processes ,Physics ,Asymptotic analysis ,Mechanical Engineering ,Gaussian ,Monte Carlo method ,General Physics and Astronomy ,Mechanics ,symbols.namesake ,Distribution function ,Classical mechanics ,Distribution (mathematics) ,Skewness ,symbols ,Two-phase flow ,Suspension (vehicle) - Abstract
The velocity distribution function of a dilute bidisperse particle-gas suspension depends on the relative magnitudes of the viscous relaxation time, τv, and the time between successive collisions, τv. The The distribution functions in the two asymptotic limits, τc ⪡ τv and τv ⪡ τc, which were analysed previously are qualitatively very different. In the former limit, the leading-order distributions are Gaussian distributions about the mean velocity of the suspension, whereas in the latter case the distributions for the two species are singular at their respective terminal velocities. Here, we calculate the properties of the suspension for intermediate values of τv/τc by approximating the distribution function as a composite Gaussian distribution. This distribution reduces to a Gaussian distribution in the limit τv ⪡ τc, in agreement with previous asymptotic analysis. In the intermediate regime, however, the composite Gaussian has a non-zero skewness, which is a salient feature of the distribution in the limit τv ⪡ τc. We have also performed numerical calculations using the direct-simulation Monte Carlo method. The approximate values for the moments of the velocity distribution obtained using the composite Gaussian compare well with the full numerical solutions for all values of τv/τc.
- Published
- 1993
35. Communications: Wall free capillarity and pendant drop removal
- Author
-
Feng Ming Chang, Yu Jane Sheng, Siang Jie Hong, Seong Heng Chan, and Heng Kwong Tsao
- Subjects
Convection ,Ostwald ripening ,Microchannel ,Materials science ,business.industry ,Drop (liquid) ,General Physics and Astronomy ,Mechanics ,Curvature ,Condensed Matter::Soft Condensed Matter ,Physics::Fluid Dynamics ,symbols.namesake ,Optics ,Sessile drop technique ,symbols ,Physical and Theoretical Chemistry ,business - Abstract
When a sessile drop encounters a pendant drop through a hole, it is generally anticipated that they will coalesce and flow downward due to gravity. However, like “wall-free” capillarity, we show that the pendant drop may be sucked up by a sliding drop instantaneously if the radius of the curvature of the former is smaller than that of the later. This phenomenon can be explained by Laplace–Young equation and convective Ostwald ripening. Our results indicate that superhydrophilic perforated surface can be used as an effective way for the removal of small droplets adhering to the inner walls of microchannel systems.
- Published
- 2010
36. The interactions between surfactants and vesicles: dissipative particle dynamics
- Author
-
Chun Min Lin, Yu Jane Sheng, Kuei Chun Huang, and Heng Kwong Tsao
- Subjects
Octyl glucoside ,Models, Molecular ,Liposome ,Molecular Structure ,Chemistry ,Vesicle ,Bilayer ,Dissipative particle dynamics ,General Physics and Astronomy ,Water ,Micelle ,Lipids ,chemistry.chemical_compound ,Colloid ,Surface-Active Agents ,Chemical engineering ,Pulmonary surfactant ,Solubility ,Organic chemistry ,Computer Simulation ,Physical and Theoretical Chemistry ,Hydrophobic and Hydrophilic Interactions ,Micelles - Abstract
The interactions between surfactants and vesicles formed by double-tail amphiphiles are investigated by the dissipative particle dynamics. As the surfactant concentration is increased, vesicle solubilization can be generally described by the three-stage hypothesis including vesicular region, vesicle-micelle coexistence, and mixed micellar region. We study the partition of surfactants between the bilayer phase and the aqueous phase where a higher value of K indicates that more surfactant molecules are incorporated in the bilayer. It is found that ln(K(-1)) is proportional to the hydrophile-lipophile balance (HLB), which depicts the degree of hydrophilicity associated with a surfactant. As the overall hydrophilicity of surfactants increases, i.e., higher HLB, K declines and vice versa. When the amounts of surfactants reach a critical point, the solubilization begins and the coexistence of vesicles and mixed micelles is observed. Further increase in the surfactant concentration results in total collapse of the vesicle. Consistent with experimental observations, the three stages are identified through the vesicle size-surfactant concentration relation. Our simulations clearly demonstrate the process of the vesicle solubilization and confirm the validity of the three-stage hypothesis.
- Published
- 2009
37. Equilibrium sedimentation profile of dilute, salt-free charged colloids
- Author
-
Yu Jane Sheng, Tzu Yu Wang, Heng Kwong Tsao, and Hsien Tsung Li
- Subjects
inorganic chemicals ,chemistry.chemical_classification ,endocrine system ,Sedimentation (water treatment) ,digestive, oral, and skin physiology ,Intermolecular force ,Monte Carlo method ,General Physics and Astronomy ,Bjerrum length ,Electrostatics ,complex mixtures ,body regions ,Colloid ,chemistry ,Chemical physics ,Computational chemistry ,Counterion condensation ,Physical and Theoretical Chemistry ,Counterion - Abstract
The sedimentation profile of a dilute colloidal solution follows the barometric distribution owing to the balance between gravitational force and thermal fluctuation. However, the electrostatic interactions may lead to significant deviation even in the low volume fraction limit (e.g., 10(-5)). On the basis of Monte Carlo simulations for a dilute, salt-free colloidal dispersion, five regimes can be identified through the resulting colloidal sedimentation profile and the counterion distribution. The electrostatic interactions depends on the Coulomb strength E(c) defined as the ratio of the Bjerrum length to the colloid size. At weak colloid-ion attractions (small E(c)), counterions tend to distribute uniformly in the container. However, both barometric and inflated profiles of colloids can be observed. On the contrary, at strong colloid-ion attraction (large E(c)), counterions accumulate in the vicinity of the colloids. Significant counterion condensation effectively decreases the strength of colloid-colloid repulsion and barometric profile of colloids can be obtained as well. As a result, the sedimentation profile and counterion distribution are indicative of the strength of effective colloid-colloid and colloid-ion interactions. It is also found that local electroneutrality condition is generally not satisfied and charge separation (or internal electric field) is neither a sufficient nor necessary condition for nonbarometric distributions.
- Published
- 2008
38. Electrophoretic size separation of particles in a periodically constricted microchannel
- Author
-
Yu Jane Sheng, Heng Kwong Tsao, Kuang Ling Cheng, and Shaoyi Jiang
- Subjects
Electrophoresis ,Microchannel ,Chemistry ,Microfluidics ,Analytical chemistry ,General Physics and Astronomy ,Field strength ,DNA ,Molecular physics ,Models, Chemical ,Electric field ,Dynamic electrophoretic mobility ,Particle ,Nanotechnology ,Electrophoretic light scattering ,Physical and Theoretical Chemistry ,Particle Size ,Brownian motion - Abstract
The size separation of Brownian particles with the same free mobility in an electrophoretic microchannel with alternating thick regions and narrow constrictions is studied theoretically. The electrophoretic mobility is field dependent and generally increases with field strength. In weak fields, Brownian diffusion dominates and the migration is controlled by the entrance effect. Therefore, smaller particles migrate faster than larger ones. In strong fields, however, the particle tends to follow electric field lines. Smaller particles are susceptible to Brownian motion and thus influenced by the nonuniform electric field in the well significantly. As a result, larger particles possess higher mobilities. Our simulation results agree with the experimental observations and provide guidance for efficient nanofluidic separation.
- Published
- 2008
39. Forced dissociation of a biomolecular complex under periodic and correlated random forcing
- Author
-
Yu Jane Sheng, Hsuan-Yi Chen, Han Jou Lin, and Heng Kwong Tsao
- Subjects
Chemical Phenomena ,Chemistry ,Stochastic process ,Chemistry, Physical ,General Physics and Astronomy ,Electrons ,Models, Theoretical ,Random forcing ,Molecular physics ,Biochemistry ,Phase lag ,Dissociation (chemistry) ,Adiabatic theorem ,Amplitude ,Models, Chemical ,Quantum mechanics ,Biomolecular complex ,Physical and Theoretical Chemistry ,Langevin dynamics - Abstract
The dissociation of a biomolecular complex under the action of periodic and correlated random forcing is studied theoretically. The former is characterized by the period tau p and the latter by the correlation time tau r. The rupture rates are calculated by overdamped Langevin dynamics and three distinct regimes are identified for both cases by comparison to local relaxation time tau R and bond lifetime T. For periodic forcing, the adiabatic approximation cannot be applied in the regime tau ptau R and the bond lifetime is determined by the average pulling. As tau Rtau pT, the rupture rate is enhanced by periodic forcing but is tau(p) independent. Analytical expressions are obtained for small and large force amplitudes. As Ttau p, the rupture rate depends on the phase lag and the process behaves like it is under constant force or loading rate. The result of correlated random forcing is similar to that of periodic forcing. Since the fluctuating forces greater than the average force F contribute more than the fluctuating forces less than F, the force fluctuations enhance the rupture rate. As Ttau r, the pulling felt by the bond before rupture cannot follow the random forcing protocol and, thus, force fluctuations decline with increasing tau r.
- Published
- 2008
40. Effects of multivalent salt addition on effective charge of dilute colloidal solutions
- Author
-
Tzu Yu Wang, Yu Jane Sheng, and Heng Kwong Tsao
- Subjects
chemistry.chemical_classification ,Quantitative Biology::Biomolecules ,Analytical chemistry ,General Physics and Astronomy ,Charge (physics) ,Charged particle ,Effective nuclear charge ,Ion ,Condensed Matter::Soft Condensed Matter ,Electrophoresis ,Colloid ,Ionic potential ,chemistry ,Chemical physics ,Physical and Theoretical Chemistry ,Counterion - Abstract
The effective charge Z* is often invoked to account for the accumulation of counterions near the colloid with intrinsic charge Z. Although the ion concentrations c(i) are not uniform in the solution due to the presence of the charged particle, their chemical potentials are uniform everywhere. Thus, on the basis of ion chemical potential, effective ion concentrations c(i)*, which can be experimentally measured by potentiometry, are defined with the pure salt solution as the reference state. The effective charge associated with the charged particle can then be determined by the global electroneutrality condition. Monte Carlo simulations are performed in a spherical Wigner-Seitz cell to obtain the effective charge of the colloid. In terms of the charge ratio alpha=Z*/Z, the effects of added salt concentration, counterion valency, and particle charge are examined. The effective charge declines with increasing salt concentration and the multivalent salt is much more efficient in reducing the effective charge of the colloidal solution. Moreover, the extent of effective charge reduction is decreased with increasing intrinsic charge for a given concentration of added salt. Those results are qualitatively consistent with experimental observations by electrophoresis.
- Published
- 2006
41. Bell's expression and the generalized Garg form for forced dissociation of a biomolecular complex
- Author
-
Yu Jane Sheng, Hsuan-Yi Chen, Han Jou Lin, and Heng Kwong Tsao
- Subjects
Physics ,Macromolecular Substances ,General Physics and Astronomy ,Binding potential ,Thermodynamics ,Activation energy ,Dissociation (chemistry) ,Reaction coordinate ,Models, Chemical ,Biomolecular complex ,Loading rate ,Physical chemistry ,Computer Simulation ,Constant force ,Maxima ,Protein Binding - Abstract
The dissociation of a biomolecular complex under the action of constant force, constant loading rate, and periodic force is studied theoretically. We show that the celebrated Bell expression provides a good approximation for the bond dissociation rate when F/F(c)<
- Published
- 2006
42. Conformational entropy of a pseudoknot polymer
- Author
-
You Chin Mou, Yu Jane Sheng, and Heng Kwong Tsao
- Subjects
Polymers ,Entropy ,Crossover ,Monte Carlo method ,Binding energy ,Molecular Conformation ,General Physics and Astronomy ,Thermodynamics ,RNA, Messenger ,Physical and Theoretical Chemistry ,Probability ,Models, Statistical ,Chemistry ,Temperature ,Hard spheres ,DNA ,Conformational entropy ,Models, Theoretical ,Crystallography ,Kinetics ,Polymerization ,Nucleic Acid Conformation ,RNA ,Pseudoknot ,Monte Carlo Method ,Algorithms ,Macromolecule - Abstract
The thermodynamics and kinetics of ABAB pseudoknot formation owing to reversible intrachain reactions are investigated for a flexible polymer based on the off-lattice Monte Carlo simulations. The polymer is made of N hard spheres tethered by inextensible bonds and consists of two reactive pairs AA and BB with binding energies -epsilon1 and -epsilon2, respectively, and three loop lengths (l1, l2, and l3). Although two intermediate states, loops A and B, may be formed, the folding path goes mainly through the intermediate loop whose free energy reduction associated with coil-to-loop crossover is greater. The conformational entropy loss is found to follow DeltaS=alpha ln N+G, where alpha approximately 2.48 for coil-loop crossover and alpha approximately 2.43 for loop-pseudoknot crossover. The constant G depends on the three loop lengths and the two end-to-reactive site lengths (L1 and L2). For a given total loop length, G is maximum when the three loop lengths are equal (l1=l2=l3). When l1=l3, the entropy loss is minimum if l2=0. However, the condition l1 not equal l3 makes G even smaller. This consequence indicates that asymmetry in loop lengths is thermodynamically favorable and this fact is consistent with observations of pseudoknotted RNA structures.
- Published
- 2006
43. Counterion condensation and release in micellar solutions
- Author
-
Tzu Yu Wang, Heng Kwong Tsao, and Chin Chieh Hsiao
- Subjects
inorganic chemicals ,chemistry.chemical_classification ,Chemistry ,Inorganic chemistry ,General Physics and Astronomy ,Ionic bonding ,Thermodynamics ,Micelle ,Degree of ionization ,Pulmonary surfactant ,Counterion condensation ,Critical micelle concentration ,Micellar solutions ,Physical and Theoretical Chemistry ,Counterion - Abstract
Counterion condensation and release in micellar solutions are investigated by direct measurement of counterion concentration with ion-selective electrode. Monte Carlo simulations based on the cell model are also performed to analyze the experimental results. The degree of counterion condensation is indicated by the concentration ratio of counterions in the bulk to the total ionic surfactant added, alphaor =1. The ionic surfactant is completely dissociated below the critical micelle concentration (cmc). However, as cmc is exceeded, the free counterion ratio alpha declines with increasing the surfactant concentration and approaches an asymptotic value owing to counterion condensation to the surface of the highly charged micelles. Micelle formation leads to much stronger electrostatic attraction between the counterion and the highly charged sphere in comparison to the attraction of single surfactant ion with its counterion. A simple model is developed to obtain the true degree of ionization, which agrees with our Monte Carlo results. Upon addition of neutral polymer or monovalent salts, some of the surfactant counterions are released to the bulk. The former is due to the decrease of the intrinsic charge (smaller aggregation number) and the degree of ionization is increased. The latter is attributed to competitive counterion condensation, which follows the Hefmeister series. This consequence indicates that the specific ion effect plays an important role next to the electrostatic attraction.
- Published
- 2005
44. Charge renormalization of charged spheres based on thermodynamic properties
- Author
-
Tzu Yu Wang, Wei Lun Hsin, Heng Kwong Tsao, and Yu Jane Sheng
- Subjects
Condensed matter physics ,Chemistry ,Monte Carlo method ,General Physics and Astronomy ,Dielectric ,Molecular physics ,Effective nuclear charge ,Charged particle ,Condensed Matter::Soft Condensed Matter ,Renormalization ,symbols.namesake ,Debye–Hückel equation ,Volume fraction ,symbols ,SPHERES ,Physical and Theoretical Chemistry - Abstract
At strong electrostatic coupling, counterions are accumulated in the vicinity of the surface of the charged particle with intrinsic charge Z. In order to explain the behavior of highly charged particles, effective charge Z(*) is therefore invoked in the models based on Debye-Huckel approximation, such as the Derjaguin-Landau-Verwey-Overbeek potential. For a salt-free colloidal suspension, we perform Monte Carlo simulations to obtain various thermodynamic properties omega in a spherical Wigner-Seitz cell. The effect of dielectric discontinuity is examined. We show that at the same particle volume fraction, counterions around a highly charged sphere with Z may display the same value of omega as those around a weakly charged sphere with Z(*), i.e., omega(Z)=omega(Z(*)). There exists a maximally attainable value of omega at which Z=Z(*). Defining Z(*) as the effective charge, we find that the effective charge passes through a maximum and declines again due to ion-ion correlation as the number of counterions is increased. The effective charge is even smaller if one adopts the Debye-Huckel expression omega(DH). Our results suggest that charge renormalization can be performed by chemical potential, which may be observed in osmotic pressure measurements.
- Published
- 2004
45. Effects of surfactant micelles on viscosity and conductivity of poly(ethylene glycol) solutions
- Author
-
Tzu Chien Wei, Heng Kwong Tsao, Wun Bin Chen, and Shun Cheng Wang
- Subjects
chemistry.chemical_classification ,General Physics and Astronomy ,Viscometer ,Interaction energy ,Polymer ,Polymer adsorption ,Micelle ,chemistry.chemical_compound ,Pulmonary surfactant ,chemistry ,Chemical engineering ,Critical micelle concentration ,Polymer chemistry ,Physical and Theoretical Chemistry ,Ethylene glycol - Abstract
The neutral polymer-micelle interaction is investigated for various surfactants by viscometry and electrical conductometry. In order to exclude the well-known necklace scenario, we consider aqueous solutions of low molecular weight poly(ethylene glycol) (2-20)x10(3), whose radial size is comparable to or smaller than micelles. The single-tail surfactants consist of anionic, cationic, and nonionic head groups. It is found that the viscosity of the polymer solution may be increased several times by micelles if weak attraction between a polymer segment and a surfactant exists, epsilon
- Published
- 2004
46. Diffusion and surface excess of a confined nanoswimmer dispersion
- Author
-
Hsuan-Yi Chen, Zhengjia Wang, Song Xiao, Yu Jane Sheng, and Heng Kwong Tsao
- Subjects
Surface Properties ,Chemistry ,Dissipative particle dynamics ,General Physics and Astronomy ,Thermodynamics ,Thermal diffusivity ,Molecular physics ,Diffusion ,Mean squared displacement ,symbols.namesake ,Colloid ,Gibbs isotherm ,symbols ,Nanoparticles ,Colloids ,Physical and Theoretical Chemistry ,Diffusion (business) ,Dispersion (water waves) ,Brownian motion - Abstract
The diffusivity and surface excess of nanoswimmers which are confined in two plates with the separation H are explored by dissipative particle dynamics. Both mean squared displacement and velocity autocorrelation function methods are used to study the diffusive behavior of nanoswimmers with the Brownian diffusivity D0 and the results obtained from both methods are consistent. The active diffusivity of confined nanoswimmers (D - D0) depends on the wall separation, swimming speed v(a), and run time τ. Our simulation results show that (D-D0)/v(a)(2)τ is a function of v(a)τ/H. The reduction in the diffusivity of active colloids is more significant than that of passive particles. The distribution of nanoswimmers between two parallel walls is acquired and two regions can be identified. The accumulation of nanoswimmers near walls is quantitatively described by the surface excess Γ. It is found that Γ grows as the nanoswimmer concentration c(b), swimming speed v(a), and run time τ are increased. The coupling between the ballistic trajectory of nanoswimmers and the walls results in nanoswimmer accumulation. The simulation outcomes indicate that Γ/Hc(b) is a function of H/v(a)τ.
- Published
- 2014
47. Colloidosomes formed by nonpolar/polar/nonpolar nanoball amphiphiles
- Author
-
Yu Jane Sheng, Sheng Hung Tu, Heng Kwong Tsao, and Hung Yu Chang
- Subjects
Models, Molecular ,Aqueous solution ,Chemistry ,Stereochemistry ,Vesicle ,Bilayer ,Static Electricity ,Dissipative particle dynamics ,Molecular Conformation ,Water ,General Physics and Astronomy ,Micelle ,Crystallography ,Membrane ,Models, Chemical ,Computer Simulation ,Colloids ,Fullerenes ,Self-assembly ,Physical and Theoretical Chemistry ,Lipid bilayer ,Hydrophobic and Hydrophilic Interactions ,Nanospheres - Abstract
Fullerene-based amphiphiles are able to form bilayer vesicles in aqueous solution. In this study, the self-assembly behavior of polymer-tethered nanoballs (NBs) with nonpolar/polar/nonpolar (n-p-n') motif in a selective solvent is investigated by dissipative particle dynamics. A model NB bears two hydrophobic polymeric arms (n'-part) tethered on an extremely hydrophobic NB (n-part) with hydrophilic patch (p-part) patterned on its surface. Dependent on the hydrophobicity and length of tethered arms, three types of aggregates are exhibited, including NB vesicle, core-shell micelle, and segmented-worm. NB vesicles are developed for a wide range of hydrophobic arm lengths. The presence of tethered arms perturbs the bilayer structure formed by NBs. The structural properties including the order parameter, membrane thickness, and area density of the inner leaflet decrease with increasing the arm length. These results indicate that for NBs with longer arms, the extent of interdigitation in the membrane rises so that the overcrowded arms in the inner corona are relaxed. The transport and mechanical properties are evaluated as well. As the arm length grows, the permeability increases significantly because the steric bulk of tethered arms loosens the packing of NBs. By contrast, the membrane tension decreases owing to the reduction of NB/solvent contacts by the polymer corona. Although fusion can reduce membrane tension, NB vesicles show strong resistance to fusion. Moreover, the size-dependent behavior observed in small liposomes is not significant for NB vesicles due to isotropic geometry of NB. Our simulation results are consistent with the experimental findings.
- Published
- 2014
48. Translation Drag Coefficient of a Self-Similar Assembly of Spheres Immersed in an Incompressible Fluid
- Author
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Heng Kwong Tsao, Shing Bor Chen, and Chin Yao Tseng
- Subjects
Physics ,Drag coefficient ,Screening effect ,Quantum mechanics ,Dimension (graph theory) ,Compressibility ,General Physics and Astronomy ,SPHERES ,Tensor ,Lambda ,Scaling - Abstract
On the basis of deterministic fractals and the Rotne-Prager hydrodynamic interaction tensor, we confirm the asymptotic as well as the finite size scaling of the friction coefficient $\ensuremath{\lambda}$ of a self-similar structure. The fractal assembly is made of $N$ spheres with its dimension varying from $Dl1$ to $D\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}3$. The number of spheres can be as high as $N\ensuremath{\sim}O({10}^{4})$. The asymptotic scaling behavior of the friction coefficient per sphere is $\ensuremath{\lambda}\ensuremath{\sim}{N}^{1/D\ensuremath{-}1}$ for $Dg1$, $\ensuremath{\lambda}\ensuremath{\sim}(\mathrm{ln}N{)}^{\ensuremath{-}1}$ for $D\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$, and $\ensuremath{\lambda}\ensuremath{\sim}{N}^{0}$ for $Dl1$. The crossover behavior indicates that while in the regime of $Dg1$ the hydrodynamic screening effect grows with the size, for $Dl1$ it is limited in a finite range, which decays with decreasing $D$.
- Published
- 2001
- Full Text
- View/download PDF
49. Ion Fluctuations within an Aqueous Microdroplet in an Apolar Medium
- Author
-
Yu Jane Sheng and Heng Kwong Tsao
- Subjects
Aqueous solution ,Materials science ,Chemical physics ,Quantum mechanics ,General Physics and Astronomy ,Ion - Abstract
Physical Review Letters
- Published
- 2001
- Full Text
- View/download PDF
50. Nonequilibrium relaxation times in polymer knot groups
- Author
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Heng Kwong Tsao, Yu Jane Sheng, and Pik Yin Lai
- Subjects
Physics ,Knot (unit) ,Chain (algebraic topology) ,Group (mathematics) ,Quantum mechanics ,Monte Carlo method ,Relaxation (NMR) ,General Physics and Astronomy ,Non-equilibrium thermodynamics ,Interaction energy ,Mathematics::Geometric Topology ,Spectrum (topology) - Abstract
Flexible polymer knots with strict topological constraint of no segment crossing are studied by Monte Carlo simulations. The nonequilibrium relaxation time of an equilibrated polymer knot cut at one point to relax to a linear chain is measured. Prime knots up to 20 essential crossings from the groups (3(1),5(1),7(1),...), (4(1),6(1),8(1),...) and (5(2),7(2),9(2),...), (6(2),8(2),10(2),...) are studied. The nonequilibrium relaxation time for knots within a group are found to increase stepwise linearly with the number of essential crossings of the original knot. Our results suggest an equally spaced topological interaction energy spectrum for knots in the same group and thus provide a quantitative description of topological interactions.
- Published
- 2000
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