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We propose a discrete lattice model of the energy of dislocations in three-dimensional crystals which properly accounts for lattice symmetry and geometry, arbitrary harmonic interatomic interactions, elastic deformations and discrete crystallographic slip on the full complement of slip systems of the crystal class. Under the assumption of diluteness, we show that the discrete energy converges, in the sense of Γ-convergence, to a line-tension energy defined on Volterra line dislocations, regarded as integral vector-valued currents supported on rectifiable curves. Remarkably, the line-tension limit is of the same form as that derived from semidiscrete models of linear elastic dislocations based on a core cutoff regularization. In particular, the line-tension energy follows from a cell relaxation and differs from the classical ansatz, which is quadratic in the Burgers vector. [ABSTRACT FROM AUTHOR]

Wettability of mold flux on stainless steel is a very important index to reflect the possibility of slag entrapment during the continuous casting process. In this study, the wetting behavior of mold flux droplet with different size on stainless steel is investigated using sessile drop method. Results show that the contact angle at 1573 K increases from 64.62 ± 0.25°, 62.56 ± 0.2° to 61.46 ± 0.2° and 60.56 ± 0.2°, with the size of the original flux sample increasing from 3, 4 to 5 and 6 mm. No chemical reaction occurs at the interface between mold flux and steel substrate via the thermodynamic calculation and microstructure analyses. Furthermore, the line tension of flux droplet/stainless steel/Ar‐5%H2 system ranges from 160.55 to 125.19 mN m−1 at the temperature range of 1473–1573 K. It is due to the positive line tension (line energy) which decreases the wettability of flux droplet on steel substrate and results in an increase of contact angle when the droplet size reduces. [ABSTRACT FROM AUTHOR]

Molecular dynamics simulations for calculation of the contact angle of surface nanodroplets and solid–liquid surface tension γ sl of linear triocontane (C 30 , left image) and four of its branched isomers (centre image is for 2,6,13,17, tetrapropyloctadecane (C 18 (C 3) 4)) are used to calculate line tension τ. The results reveal (left plots) that γ sl and line tension τ depend on surface oleophilicity/oleophobicity and molecular degree of branching (DB*). [Display omitted] • Developed a novel MD calculation method of surface nanodroplet line tension (τ). • Calculated Solid-liquid surface tension γ sl of linear and branched liquid alkanes, showed deviation from Young equation. • γ sl and τ signs depend on surface wettability, and their magnitude reduce with increased branching. • On the oleophilic surface, positive line tensions in the order of 10-10 for all alkanes. • On the oleophobic surface, τ is two orders of magnitude lower for branched alkanes. Surface nanodroplets have important technological applications. Previous experiments and simulations have shown that their contact angle deviates from Young's equation. A modified version of Young's equation considering the three-phase line tension (τ) has been widely used in literature, and a wide range of values for τ are reported. We have recently shown that molecular branching affects the liquid–vapour surface tension γ lv of liquid alkanes. Therefore, the wetting behaviour of surface nanodroplets should be affected by molecular branching. This study conducted molecular dynamics (MD) simulations to gain insight into the wetting behaviour of linear and branched alkane nanodroplets on oleophilic and oleophobic surfaces. We aim to examine the Young equation's validity and branching's effect on fundamental properties, including solid–liquid surface tension γ sl and line tension τ. The simulations were performed on a linear alkane, triacontane (C 30 H 62), as well as four of its branched isomers: 2,6,13,17-tetrapropyloctadecane,2,6,9,10,13,17-hexaethyloctadecane, 2,5,7,8,11,12,15-heptaethylhexadecane and 2,3,6,7,10,11-hexapropyldodecane. Nanodroplets with a diameter of approximately 15 nm were released onto the surfaces, and their contact angles were measured. Additionally, using a novel approach, the solid–liquid surface tension (γ sl), the validity of Young's equation and line tension for all alkane and surface combinations are determined. It was discovered that the calculated γ sl , deviated from the theoretical γ sl , Young predicted from Young's equation for all alkanes on oleophilic surfaces. However, this deviation was minimal for branched alkanes on the oleophobic surfaces but more significant for the linear alkane. The findings indicated that γ sl < 0 for oleophilic surfaces and γ sl > 0 for oleophobic surfaces. Moreover, it was observed that | γ sl | was lower for branched molecules and decreased as branching increased. Line tension values were then determined through a novel method, showing τ was positive for oleophilic surfaces ranging from 1.30 × 10-10 to 6.27 × 10-11N. On an oleophobic surface, linear alkane shows a negative line tension of −1.15 × 10-10N and branched alkanes up to two orders of magnitude lower values ranging from −2.09 × 10-12 to 2.43 × 10-11N. Line tension values between −1.15 × 10-10 and + 1.1 × 10-10N are calculated for various linear alkane and surface combinations. These findings show the dependence of line tension on the contact angle and branching, demonstrating that for linear alkanes, τ is significant, whereas, for branched alkanes, line tension is smaller or negligible for large contact angles. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate whether it is possible to prevent oolemma lysis after Piezo-assisted intracytoplasmic sperm injection (Piezo-ICSI) caused by abnormal membrane rupture. A total of 489 mature oocytes were obtained from 85 patients who underwent Piezo-ICSI in an infertility clinic. Inseminated oocytes were classified into the following two groups: normal rupture and abnormal rupture, and a portion of abnormally ruptured oocytes was randomly exposed to 7% PVP solution. Normal fertilization rate, degeneration rate, proportion of high-quality embryos on day 3, blastocyst formation, and morphologically high-quality blastocysts were compared. Abnormal rupture was defined as cytoplasmic membrane rupture before piezo pulse driving. Among the abnormal rupture groups, the normal fertilization and degeneration rates were compared between the high-stretched (ruptured at ≥ 50% during oocyte membrane stretching) and low-stretched (< 50% position) oocytes. The degeneration rate was significantly higher in abnormally ruptured oocytes than in normally ruptures oocytes (14.3% vs 1.3%, p < 0.001), and there was no significant difference in embryonic development after fertilization. PVP treatment immediately after oolemma rupture significantly decreased the degeneration rate (6.0% vs 19.7%, p = 0.031) and increased the normal fertilization rate. Similarly, there were no significant differences in the developmental potential. Furthermore, pregnancy outcome data showed no significant differences in pregnancy and live birth rates. The degeneration rate was reduced by treating low-stretched oocytes with PVP. Exposure to polyvinylpyrrolidone (PVP) immediately after abnormal membrane rupture represents an effective strategy to prevent oocyte degeneration. This is the first study to propose a strategy for the prevention of oocyte degeneration in Piezo-ICSI. These findings are expected to reduce the oocyte degeneration rate and increase normal fertilization rate as well as assist patients who can only acquire oocytes with weak plasma membranes. [ABSTRACT FROM AUTHOR]

We have studied the process of electroporation of bilayer lipid membranes (BLMs) made of dioleoylphosphatidylcholine (DOPC). We obtained experimental data on the average lifetime of the membrane as a function of applied transmembrane voltage in the range of 200–375 mV. The analysis of the obtained data showed that the dependence is nonmonotonic and cannot be described in terms of the classical theory of electroporation. These results are consistent with modern models of the process of formation of through conductive pores in a membrane. The above models imply a complex pore energy profile and its dependence on a membrane tension and an external electric field. Thus, we have shown that the classical theory of electroporation does not satisfy the experimentally observed dependencies of the average membrane lifetime on the applied potential difference and requires further refinement. [ABSTRACT FROM AUTHOR]

There exist many ways to calculate the contact angle of a sessile droplet on a planar surface on the basis of molecular modeling data, and the result may depend on the chosen approach. This paper presents molecular dynamics simulations of argon and water sessile droplets on simple model and more complex atomistic substrates. Several approaches for calculating contact angles are described. These approaches are based on an analysis of instantaneous droplet's configurations and averaged density profiles. The latter are analyzed using density cutoffs and the Sobel filters. Parameters of the interaction between the planar surface and the fluid are being tuned in order to consider model lyophilic and lyophobic substrates. Dependences of the contact angle on the strength of interaction between the fluid and the substrate and on the droplet size are obtained. The apparent line tensions for the observed sessile droplets are evaluated. • Contact angles of argon and water sessile droplets on planar surfaces are calculated. • Dependences of contact angle on temperature and droplet size are obtained. • Four different approaches for contact angle calculation are implemented. • The obtained contact angle value may depend on the way of its calculation. • Sign of the apparent line tension is different for argon and water sessile droplets. [Display omitted] [ABSTRACT FROM AUTHOR]

Antimicrobial activity of some amphipathic peptides is associated with the formation of through pores in bacterial membranes. Antimicrobial peptides (AMPs) specifically bind to the plasma membrane by incorporating their hydrophobic regions into the outer lipid monolayer. The membrane is inevitably deformed. Many AMPs form so-called toroidal pores, the edge of which is partially lined with peptide molecules. The edge of the pore is characterized by significant deformations. In this work, we calculated the energy of the pore edge, with amphipathic peptides located on the pore equator, as well as the energy of deformations induced by AMP in a planar lipid bilayer. It was shown that for certain physicochemical and geometric characteristics of the AMP molecule the energy of the pore, on the equator of which two or more peptide molecules are located, can be lower than the energy of deformations induced in the planar bilayer by the same number of peptide molecules. Thus, two AMP molecules can, in principle, form a through pore in the membrane, although this is possible only in a fairly narrow range of physicochemical and geometric characteristics of the peptides. [ABSTRACT FROM AUTHOR]

Osmotic pressure can break the fluid balance between intracellular and extracellular solutions. In hypo-osmotic solution, water molecules, which transfer into the cell and burst, are driven by the concentration difference of solute across the semi-permeable membrane. The complicated dynamic processes of intermittent bursts have been previously observed. However, the underlying physical mechanism has yet to be thoroughly explored and analyzed. Here, the intermittent release of inclusion in giant unilamellar vesicles was investigated quantitatively, applying the combination of experimental and theoretical methods in the hypo-osmotic medium. Experimentally, we adopted a highly sensitive electron multiplying charge-coupled device to acquire intermittent dynamic images. Notably, the component of the vesicle phospholipids affected the stretch velocity, and the prepared solution of vesicles adjusted the release time. Theoretically, we chose equations and numerical simulations to quantify the dynamic process in phases and explored the influences of physical parameters such as bilayer permeability and solution viscosity on the process. It was concluded that the time taken to achieve the balance of giant unilamellar vesicles was highly dependent on the molecular structure of the lipid. The pore lifetime was strongly related to the internal solution environment of giant unilamellar vesicles. The vesicles prepared in viscous solution were able to visualize long-lived pores. Furthermore, the line tension was measured quantitatively by the release velocity of inclusion, which was of the same order of magnitude as the theoretical simulation. In all, the experimental values well matched the theoretical values. Our investigation clarified the physical regulatory mechanism of intermittent pore formation and inclusion release, which provides an important reference for the development of novel technologies such as gene therapy based on transmembrane transport as well as controlled drug delivery based on liposomes. [ABSTRACT FROM AUTHOR]

Vapor condensation is widely adopted in thermal management technology and condenser of energy power plant, benefiting from its high heat transfer coefficient. Contact angle is the key factor to regulate vapor condensation rate, leading to the rapid development of surfaces with various wettability fabricated by micro/nanoengineering. However, the nucleated nanodroplets (1–100 nm) at the beginning of condensation exhibit different wetting dynamics from macroscopic droplets, the mechanisms of which are not well understood. In this work, we perform molecular dynamic (MD) simulations to study the evolution of contact angle during nanodroplet nucleation processes. The results show the nucleated contact angle of a nanodroplet is smaller than the contact angle predicted by the classical Young equation on a hydrophobic surface, while it is opposite for nanodroplet nucleating on hydrophilic surface. Moreover, we have calculated line tension for the nucleated nanodroplet on the surfaces with different wettability to explain this discovery, and found positive line tension on hydrophobic surface, while negative line tension for nucleated nanodroplet on hydrophilic surface. Furthermore, the calculated line tension, which is at the order magnitude of 10−11 J/m, aligns well with the data documented in the literature. • Contact angle of nucleated nanodroplet on hydrophobic surface is smaller than Young contact angle. • Positive line tension is found on hydrophobic surface, while negative line tension for nanodroplet on hydrophilic surface. • The calculated magnitude of line tension is at the order of 10−11 J/m, which is in good agreement with literature data. [ABSTRACT FROM AUTHOR]

Abstract Experimental results of dynamic contact angle measurements of low salinity brine and combined low salinity water and surfactant flooding (LSW–SF) on silica surface are presented in this study. Dynamic contact angle experiments were carried out for four crude oil samples with low salinity brines and combined low salinity and sodium dodecylbenzene sulfonate (SDBS) solutions. Similar measurements with the same ion strength in presence of different cations, Na+ and Ca2+, for low salinity injections and combined low salinity–SDBS solutions were also carried out to study the change in dynamic contact angles and wetting behavior. The presences of different cations change the initial contact angles in low salinity solution injections and show different dynamic behaviors in presence of different crude oils. The signs and values of the line tension to oil/water interfacial tension ratios have been calculated from the size dependence of the dynamic contact angle measurements on the silica coated quartz crystal microbalance sensors. Analysis indicates positive line tension values for low salinity brine systems and negative values for LSW–SF systems. Injection of surfactant solutions in presence of electrolyte prompts the spreading of the oil droplet over the surface, which is induced by interfacial tension gradient from the top of the oil droplet toward the contact line. The results indicated that spreading time, which is the required time for oil drop to gradually flatten out, is dependent on type of electrolytes and is a function of surface excess concentration of the surfactant.

Genome replication of coronaviruses takes place in specific cellular compartments, in so-called double-membrane vesicles (DMVs), formed from the endoplasmic reticulum (ER). An intensive production of DMVs is induced by non-structural viral proteins. Here, we proposed a possible mechanism of the DMV formation from ER-derived spherical vesicles where liquid-ordered and liquid-disordered lipid phases coexist. These vesicles are supposed to divide into two homogeneous liquid-ordered and liquid-disordered vesicles. The formation of two spherical vesicles constituting DMV requires a mechanical work to be performed. We considered the excess energy of the boundary between the coexisting lipid phases as the main driving force behind the division of the initial vesicle. Explicitly accounting for the energy of elastic deformations and the interphase boundary energy, we analyzed a range of physical parameters where the DMV formation is possible. We concluded that this process can principally take place in a very narrow range of system parameters. The most probable diameter of DMVs formed according to the proposed mechanism appeared to be approximately 220 nm, in an agreement with the average diameter of DMVs observed in vivo. Our consideration predicts the DMV size to be strongly limited from above. The developed analysis can be utilized for the production of DMVs in model systems.

Line tension at phase-separated lipid domain boundaries is an important factor that governs the stability of the phase separation. We studied the control of the line tension in lipid membranes composed of dioleoylphosphocholine (DOPC), dipalmitoylphosphocholine (DPPC), and cholesterol (Chol) by the addition of the following three monounsaturated fatty acids (MUFAs) with different chain lengths: palmitoleic acid (PaA), oleic acid (OA), and eicosenoic acid (EiA). In addition, we attempted to alter the line tension by applying osmotic pressure. The phase behavior of the MUFA-containing lipid membranes in the presence and absence of osmotic stress was observed by fluorescence and confocal laser scanning microscopy. The line tension was quantitatively measured from the domain boundary fluctuation by flicker spectroscopy, and the interactions between the lipids and MUFAs were examined by differential scanning calorimetry. PaA and OA, which are shorter MUFAs, decreased the line tension, whereas EiA changed the liquid domain to a solid domain. The osmotic pressure increased the line tension, even in the presence of MUFAs. It may be possible to control the line tension by combining the chemical approach of MUFA addition and the physical approach of applying osmotic pressure.

Nucleation and growth is a technique widely used to prepare colloids, in which droplets are adsorbed onto substrate particles. Changing the contact angle of the substrates can greatly alter the morphology of the product particles. Here, we investigate the nucleation and growth of 3-methacryloxypropyltrimethoxysilane (MPTMS) both onto Stöber spheres and onto (cross-linked) MPTMS* spheres. The former results in 'snowman' particles with a cap-shaped MPTMS* compartment, and we show that their morphology is highly controllable via the MPTMS content in the reaction mixture. The contact angle of the MPTMS* compartment decreases with droplet diameter, suggesting that this wetting process is affected not only by surface tension but also by line tension. In contrast to Stöber spheres, MPTMS* substrate particles yield highly reproducible and tuneable 'engulfed-sphere' colloids with an internal reference axis (but a homogeneous mass distribution). These engulfed-sphere particles can be fully index-matched for confocal microscopy on account of their homogeneous refractive index. Suitable index-matching mixtures of polar and of low-polar media are presented, where cyclohexyl iodide (CHI) is introduced as a new medium for colloids of high refractive index. Finally, the index-matched engulfed-sphere colloids are self-assembled into (close-packed and long-range) plastic phases, and the particles' rotational diffusion inside the crystal phases is tracked via confocal microscopy. [ABSTRACT FROM AUTHOR]

Unsaturated and saturated phospholipids tend to laterally segregate, especially in the presence of cholesterol. Small molecules such as neurotransmitters, toxins, drugs etc. possibly modulate this lateral segregation. The small aromatic neurotransmitter serotonin (5-HT) has been found to bind to membranes. We studied the lipid structure and packing of a ternary membrane mixture consisting of palmitoyl-oleoyl-phosphatidylcholine, palmitoyl-sphingomyelin, and cholesterol at a molar ratio of 4/4/2 in the absence and in the presence of 5-HT, using a combination of solid-state 2H NMR, atomic force microscopy, and atomistic molecular dynamics (MD) simulations. Both NMR and MD report formation of a liquid ordered (Lo) and a liquid disordered (Ld) phase coexistence with small domains. Lipid exchange between the domains was fast such that single component 2H NMR spectra are detected over a wide temperature range. A drastic restructuring of the domains was induced when 5-HT is added to the membranes at a 9 mol% concentration relative to the lipids. 2H NMR spectra of all components of the mixture showed two prominent contributions indicative of molecules of the same kind residing both in the disordered and the ordered phase. Compared to the data in the absence of 5-HT, the lipid chain order in the disordered phase was further decreased in the presence of 5-HT. Likewise, addition of serotonin increased lipid chain order within the ordered phase. These characteristic lipid chain order changes were confirmed by MD simulations. The 5-HT-induced larger difference in lipid chain order results in more pronounced differences in the hydrophobic thickness of the individual membrane domains. The correspondingly enlarged hydrophobic mismatch between ordered and disordered phases is assumed to increase the line tension at the domain boundary, which drives the system into formation of larger size domains. These results not only demonstrate that small membrane binding molecules such as neurotransmitters have a profound impact on essential membrane properties. It also suggests a mechanism by which the interaction of small molecules with membranes can influence the function of membrane proteins and non-cognate receptors. Altered membrane properties may modify lateral sorting of membrane protein, membrane protein conformation, and thus influence their function as suspected for neurotransmitters, local anesthetics, and other small drug molecules.

The paper investigates the formation and stability of the surface nanobubbles with regard to the line tension at the triple phase boundary; the pinning effect, when the bubble stands on the surface and the triple phase boundary does not move; and the Kelvin equation. It is shown that the negative line tension can cause a spontaneous nanobubble formation at the small diameter of the phase boundary curve and the small contact angle. [ABSTRACT FROM AUTHOR]

Unsaturated and saturated phospholipids tend to laterally segregate, especially in the presence of cholesterol. Small molecules such as neurotransmitters, toxins, drugs etc. possibly modulate this lateral segregation. The small aromatic neurotransmitter serotonin (5-HT) has been found to bind to membranes. We studied the lipid structure and packing of a ternary membrane mixture consisting of palmitoyl-oleoyl-phosphatidylcholine, palmitoyl-sphingomyelin, and cholesterol at a molar ratio of 4/4/2 in the absence and in the presence of 5-HT, using a combination of solid-state 2H NMR, atomic force microscopy, and atomistic molecular dynamics (MD) simulations. Both NMR and MD report formation of a liquid ordered (L o ) and a liquid disordered (L d ) phase coexistence with small domains. Lipid exchange between the domains was fast such that single component 2H NMR spectra are detected over a wide temperature range. A drastic restructuring of the domains was induced when 5-HT is added to the membranes at a 9 mol% concentration relative to the lipids. 2H NMR spectra of all components of the mixture showed two prominent contributions indicative of molecules of the same kind residing both in the disordered and the ordered phase. Compared to the data in the absence of 5-HT, the lipid chain order in the disordered phase was further decreased in the presence of 5-HT. Likewise, addition of serotonin increased lipid chain order within the ordered phase. These characteristic lipid chain order changes were confirmed by MD simulations. The 5-HT-induced larger difference in lipid chain order results in more pronounced differences in the hydrophobic thickness of the individual membrane domains. The correspondingly enlarged hydrophobic mismatch between ordered and disordered phases is assumed to increase the line tension at the domain boundary, which drives the system into formation of larger size domains. These results not only demonstrate that small membrane binding molecules such as neurotransmitters have a profound impact on essential membrane properties. It also suggests a mechanism by which the interaction of small molecules with membranes can influence the function of membrane proteins and non-cognate receptors. Altered membrane properties may modify lateral sorting of membrane protein, membrane protein conformation, and thus influence their function as suspected for neurotransmitters, local anesthetics, and other small drug molecules. [ABSTRACT FROM AUTHOR]

Forces exerted at surfaces and interphases due to formation of gaseous (air or vapor) bridges describe the extreme liquid repellence in superhydrophobicity (SH) and amphiphobicity. The neighboring research areas of liquid capillary bridges and that of interactions between hydrophobic surfaces are highly valuable reference systems. We review recent findings with particular focus on the three-phase contact line and surface forces. Although macroscopic contact angles (>150°), low contact angle hysteresis (<10°, but can be high; parahydrophobic or petal type) and low roll-off angle (≤5–10°) are adequate criteria for SH and superamphiphobicity (SA) for most studies, a detailed understanding requires a view related to mechanisms. Experimental studies of liquid drop–substrate and particle–substrate adhesion in hydrophobic, SH, and SA systems are summarized by relating measured forces to the wetting tension, γ cos θ. A low wetting tension value is a necessary but not sufficient criterion for SH and SA systems. The picture emerging from detailed force distance studies is that extreme liquid repellence in SH and SA systems is a progression of liquid repellence due to hydrophobicity, in which force curves can be explained by capillary forces of constant volume of the gaseous capillary. In SH and SA, neither the capillary force equation assuming constant volume nor constant pressure of the gaseous capillary explains experimental force measurements as the capillary increases in both volume and pressure. In recent experimental studies, a transition is observed into nonconstant volume and pressure which suggests an SH and SA wetting transition from constant volume or pressure to a capillary growth as driven by the γA and the PV works but also by forces at the three-phase contact SLV (solid-liquid-vapor) line, viz. pinning forces, F p i n and F d e p i n , and line energy, (τ L) SLV , terms. Supported by calculations of the different contributions, we suggest this transition being an appropriate definition for the onset of (appreciable) SH and SA. Image 1 • Superhydrophobicity and superamphiphobicity receive increased research and technical attention. • Force-distance studies use drop/substrate or probe/substrate summarized by wetting tensions. • Probe/surface studies show gas capillaries growing to large distances and in volume and pressure. • Thermodynamics describing curves include works of surface tension, pressure-volume and TPCL terms. [ABSTRACT FROM AUTHOR]

Line tension is calculated for a simple model of a surface nanobubble formed on a smooth hydrophobic substrate. It is shown that, with an increase in the contact angle at a certain critical value, the surface tension changes sign from positive to negative. This means that the surface tension stretches the nanobubble, increasing its radius of curvature and thereby stabilizing it. [ABSTRACT FROM AUTHOR]

We study the geometry of a stable drop of incompressible liquid constrained to lie in a spherical container. The energy functional is comprised of the surface tension, the wetting energy and the line tension. It is shown that the only stable equilibrium drops having the topology of a disc are flat discs and spherical caps. Sharp conditions for the stability of equilibrium spherical caps and flat discs are given. [ABSTRACT FROM AUTHOR]

Three-dimensional crack growth initiation is examined under the assumption that the crack front remains smooth. Two important modeling issues, specific to three-dimensional rather than two-dimensional cracks, are addressed. First, it is established that, at each point along the crack front, the velocity and configurational force are two-dimensional vectors, lying in the local normal plane. This allows one to generalize any two-dimensional crack growth criterion to three dimensions. Second, a simple mesoscopic model to account for along-the-front non-locality is proposed. This model eliminates pathological growth patterns ubiquitous to basic models applied to three-dimensional cracks. Further, the model is straightforward to use as it relies on standard fracture properties only. [ABSTRACT FROM AUTHOR]

Heterogeneous condensation of water vapor on particles is widely used in the fields of atmospheric cloud physics and industrial particulate abatement. Particles surface wettability plays a fundamental role in water vapor condensation, but a microscopic insight of the impact of particles surface wettability on vapor condensation is lacked. Therefore, the Environmental Scanning Electron Microscope (ESEM) is adopted to directly visualize vapor condensation on particles with different surface wettability at a microscopic scale. Firstly heterogeneous condensation of water vapor on the hydrophilic and hydrophobic particles is obtained by the ESEM. The results show that when water vapor condenses on the hydrophilic particles, a spherical cap-shaped embryo first appears and subsequently develops into a spherical droplet to finally wrap the single particle. While on the hydrophobic particles, a spherical cap-shaped embryo will first appear and continue to grow into a spherical droplet to finally detach from the particle. Then the wetting coefficient is introduced to characterize the wetting degree of the droplet on the particle. The wetting coefficient will increase with the decrease of the contact angle, so the wettability of water vapor on the hydrophilic particles is better than that on the hydrophobic particles. Meanwhile based on classical nucleation theory, the geometrical factor and the critical supersaturation will decrease when the contact angle decreases, making it easier for water vapor to condense on the hydrophilic particles. Finally the line tension is investigated to explain the condensation mechanism. On the hydrophilic particles, when the droplet has crossed the equatorial line of the particle, the positive line tension promotes the spreading movement of the droplet over the particle to form a wrapped spherical droplet. Therefore, there is a transition from a spherical cap-shaped embryo before crossing the equatorial line of the particle to a wrapped spherical droplet after crossing the equatorial line. While on the hydrophobic particles, the negative line tension suppresses the spreading movement of the droplet over the particle to form a detached spherical droplet. So there is a transition from a spherical cap-shaped embryo before crossing the equatorial line of the particle to a detached spherical droplet after crossing the equatorial line. • Heterogeneous condensation of water vapor on hydrophilic and hydrophobic particles is directly visualized. • A spherical cap-shaped embryo appears on the hydrophilic particle and develops into a spherical droplet to wrap the particle. • A spherical cap-shaped embryo appears on the hydrophobic particle and grows into a spherical droplet to detach from the particle. • The positive line tension promotes the spreading movement of the droplet over the hydrophilic particle. • The negative line tension suppresses the spreading movement of the droplet over the hydrophobic particle. [ABSTRACT FROM AUTHOR]

This work is concerned with analysis and refinement for a class of island dynamics models for epitaxial growth of crystalline thin films. An island dynamics model consists of evolution equations for step edges (or island boundaries), coupled with a diffusion equation for the adatom density, on an epitaxial surface. The island dynamics model with irreversible aggregation is confirmed to be mathematically ill-posed, with a growth rate that is approximately linear for large wavenumbers. By including a kinetic model for the structure and evolution of step edges, the island dynamics model is made mathematically well-posed. In the limit of small edge Peclet number, the edge kinetics model reduces to a set of boundary conditions, involving line tension and one-dimensional surface diffusion, for the adatom density. Finally, in the infinitely fast terrace diffusion limit, a simplified model of one-dimensional surface diffusion and kink convection is derived and found to be linearly stable.

The large plasticity, dynamics and adaptability of biological membranes allow different modes of intrinsic and inducible permeability. These phenomena are of physiological importance for a number of natural functions related to cell death and can also be manipulated artificially for practical purposes like gene transfer, drug delivery, prevention of infections or anticancer therapy. For these advances to develop in a controllable and specific way, we need a sufficient understanding of the membrane permeability phenomena. Since the formulation of early concepts of pore formation, there has been an enormous effort to describe membrane permeability by using theory, simulations and experiments. A major breakthrough has come recently through theoretical developments that allow building continuous trajectories of pore formation both in the absence and presence of stress conditions. The new model provides a coherent quantitative view of membrane permeabilization, useful to test the impact of known lipid properties, make predictions and postulate specific pore intermediates that can be studied by simulations. For example, this theory predicts unprecedented dependencies of the line tension on the pore radius and on applied lateral tension which explain previous puzzling results. In parallel, important concepts have also come from molecular dynamics simulations, of which the role of water for membrane permeabilization is of special interest. These advances open new challenges and perspectives for future progress in the study of membrane permeability, as experiments and simulations will need to test the theoretical predictions, while theory achieves new refinements that provide a physical ground for observations. [ABSTRACT FROM AUTHOR]

In this paper, the effect of a probe tip on the contact angle measurements and the formation process of nanobubbles based on line tension and pinning theory was investigated. In this investigation, the images of nanobubbles and micropancakes on mica(001) and molybdenite(0001) surfaces were obtained during an alcohol-water exchange by means of atomic force microscopy (AFM) in tapping mode (TMAFM). Based on the image characteristics and the theory of line tension and pinning, a new point of view is presented: the contact angle of a nanobubble is not always a large obtuse angle but is an uncertain value; its true value is affected by the curvature radius of the AFM probe tip, and the value is close to the macroscopic contact angle. Meanwhile, the formation of nanobubbles is affected by the surface tension, line tension and pinning. [ABSTRACT FROM AUTHOR]

It is believed that separation of lipid matrix of biological membranes into ordered and disordered phases plays an important role in the lateral distribution of proteins and transduction of cellular signals through the plasma membrane. In model lipid membranes with symmetric composition of monolayers, such phase separation always leads to formation of bilayer domains. However, the lipid composition of outer and inner monolayers of plasma membranes of cells is different, i.e., these membranes are asymmetric. The mechanism of coupling of monolayer domains into bilayer structures in cells still remains unexplained. The ordered lipid domain is thicker than the surrounding membrane; as a result, elastic deformations occur at their boundary. Minimization of the elastic part of the boundary energy contributes to the coupling of monolayer domains in opposite monolayers. However, this driving force is not enough to ensure that domains will come into register: at a certain fraction of the membrane area occupied by the domains, the elastic energy can reach the minimum in antisymmetric configurations (the ordered domain in the upper monolayer is opposed by disordered monolayer of the surrounding membrane). As an alternative factor of the coupling, we considered curvature thermal fluctuations of the membrane shape. Our theoretical analysis of elastic deformations in a lipid bilayer that is asymmetric in monolayer composition shows that more rigid lipid domains tend to distribute into the region with lower curvature of the monolayer; these regions naturally coincide in opposite monolayers. Thus, the coupling of ordered domains in different monolayers is provided by their greater bending stiffness as compared to the surrounding membrane. At the same time, greater ordering leads to lateral condensation, i.e., to the decrease of the average area per lipid molecule. The difference in area per lipid molecule in the coexisting membrane phases, on the contrary, tends to separate bilayer domains into their monolayer components. To quantify the coupling energy of ordered domains, it is necessary to take both of these effects into account. [ABSTRACT FROM AUTHOR]

Cross-slip is a thermally activated process by which a screw dislocation changes its slip plane. Understanding and modelling the activation barrier of the cross-slip process as a free-energy barrier that depends on the stress conditions at the vicinity of the dislocation is crucial. In this work, we employ the line-tension model for the cross-slip of screw dislocations in face-centred cubic (FCC) metals in order to calculate the energy barrier when both Escaig stresses are applied on the primary and cross-slip planes and Schmid stress is applied on the cross-slip plane. We propose a closed-form expression for the activation energy for cross-slip in a large range of stresses, without any fitting parameters. The results of the proposed model are in good agreement with previous numerical results and atomistic simulations. We also show that, when Schmid stress is applied on the cross-slip plane, the energy barrier is decreased, and in particular, cross-slip can occur even when the Escaig stress in the primary plane is smaller than that on the cross-slip plane. The proposed closed-form expression for the activation energy can be easily implemented in dislocation dynamics simulations, owing to its simplicity and universality. This will allow cross-slip to be more accurately related to macroscopic plasticity. [ABSTRACT FROM AUTHOR]

Abstract Chemically simplified lipid mixtures are used here as models of the cell plasma membrane exoplasmic leaflet. In such models, phase separation and morphology transitions controlled by line tension in the liquid-disordered (Ld) + liquid-ordered (Lo) coexistence regime have been described [1]. Here, we study two four-component lipid mixtures at different cholesterol fractions: brain sphingomyelin (BSM) or 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC)/1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC)/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/cholesterol (Chol). On giant unilamellar vesicles (GUVs) display a nanoscopic-to-macroscopic transition of Ld + Lo phase domains as POPC is replaced by DOPC, and this transition also depends on the cholesterol fraction. Line tension decreases with increasing cholesterol mole fractions in both lipid mixtures. For the ternary BSM/DOPC/Chol mixture, the published phase diagram [19] requires a modification to show that when cholesterol mole fraction is >~0.33, coexisting phase domains become nanoscopic. Graphical abstract Unlabelled Image Highlights • GUVs composed of BSM or DSPC/DOPC/POPC/Chol can be generated using electroformation. • A nanoscopic-to-macroscopic transition within Ld/Lo coexistence regime is exhibited on GUVs as POPC is replaced by DOPC. • The Chol content can control line tension and thus determine whether Ld/Lo domains are nanoscopic or macroscopic. • Line tension of 0.1–0.3 pN has been detected for initial formation of visible Ld/Lo lipid domains. • Line tension decreases as correlated with reduced thickness mismatch between the Ld and Lo phases. [ABSTRACT FROM AUTHOR]

The resistance of a dislocation to bowing under stress governs the strength of the gamut of metallic material systems. This resistance is commonly referred to as the dislocation line tension (Γ) and is employed ubiquitously within continuum scale models of metal plasticity. Despite its significance, a unifying model for the line tension of a bowing dislocation segment, which has been analytically derived and independently reproduces simulation results, remains lacking. Here, we report a model for Γ of a curved, semicircular bowing dislocation segment. Upon applying our model to the operative stress of a Frank–Read dislocation source, we predict a prelogarithmic scaling of the Frank–Read source strength in agreement with existing simulation results. Moreover, in the limit of infinitesimal bowout we predict a prelogarithmic line tension factor which also agrees with theoretical analyses. Our model provides insight into the evolution of an arbitrarily oriented, stressed dislocation segment without resorting to numerical methods. [ABSTRACT FROM AUTHOR]

Condensed domain formation of fluorinated compounds (alcohol and ester) in adsorbed films at alkane/water interfaces was investigated by interfacial tensiometry, X-ray reflectometry, and BAM observation. The results obtained are explained by the effects of contact energy and dipole-dipole interaction, which are competitive contributions to the line tension acting at the domain boundary. Estimation of the two contributions indicated that the former is more dominant than the latter for the domain formation. In the adsorbed films of fluorinated alcohol, F 8 H 2 OH, at alkane/water interfaces, the domain formation was suppressed with increasing alkane chain length due to an increase in contact energy. The mixing of hybrid alcohol with fluorocarbon and hydrocarbon chains of the same carbon number, F 6 H 6 OH, in adsorbed film reduces contact energy. This stabilizes the dispersion of many domains with small size. On the other hand, when F 8 H 2 OH molecules are mixed with a cationic surfactant, C 12 TAB, in the adsorbed film, an attractive dipole-ion interaction between the hydrophilic groups relaxes the repulsive dipole-dipole interaction between F 8 H 2 OH molecules, resulting in the formation of domains with smooth boundary and large size. Furthermore, fluorinated ester, FC 12 Me molecules form flower shaped domains with intricate boundary mainly due to a larger dipole moment of FC 12 Me than F 8 H 2 OH. [Display omitted] • Domain formation at alkane/water interface determined by a balance between contact energy and dipole-dipole repulsion. • Suppression of domain formation by increasing contact energy. • Stabilization of many small domain dispersion by lowering contact energy. • Domain formation with intricate boundary induced by increasing dipole-dipole repulsion. • Domains with large size and smooth boundary formed under reduced dipole-dipole repulsion. [ABSTRACT FROM AUTHOR]

A generalized Young’s equation, which takes into account two corrections to the line tension by the curvature dependence of the liquid-vapor surface tension and by the contact angle dependence of the intrinsic line tension, is derived from the thermodynamic free-energy minimization. The correction from the curvature dependence can be qualitatively estimated using Tolman’s formula. The correction from the contact angle dependence can be estimated for nanometer-scale droplets for which the analytical formula for the intrinsic line tension determined from the van der Waals interaction is available. The two corrections to the apparent line tension of this van der Waals nano-droplets are as small as nN, and lead to either a positive or a negative apparent line tension. The gravitational line tension for millimeter-scale droplets by the gravitational acceleration is also considered. The gravitational line tension is of the order of N so that the correction from the curvature dependence can be neglected. Yet, the contact angle dependence is so large that the apparent line tension becomes always negative though the intrinsic line tension without the correction is always positive. These two examples demonstrate clear distinction between the theoretically calculated intrinsic line tension and the experimentally determined apparent line tension which includes these two corrections. Naive comparison of the experimentally determined and the theoretically calculated line tension is not always possible. [ABSTRACT FROM AUTHOR]

Plastic deformation, at all strain rates, is accommodated by the collective motion of crystalline defects known as dislocations. Here, we extend an analysis for the energetic stability of a straight dislocation, the so-called line tension (Γ), to steady-state moving dislocations within elastically anisotropic media. Upon simplification to isotropy, our model reduces to an explicit analytical form yielding insight into the behaviour of Γ with increasing velocity. We find that at the first shear wave speed within an isotropic solid, the screw dislocation line tension diverges positively indicating infinite stability. The edge dislocation line tension, on the other hand, changes sign at approximately of the first shear wave speed, and subsequently diverges negatively indicating that the straight configuration is energetically unstable. In anisotropic crystals, the dependence of Γ on the dislocation velocity is significantly more complex; at velocities approaching the first shear wave speed within the plane of the crystal defined by the dislocation line, Γ tends to diverge, with the sign of the divergence strongly dependent on both the elastic properties of the crystal and the orientation of the dislocation line. We interpret our analyses within the context of recent molecular dynamics simulations of the motion of dislocations near the first shear wave speed. Both the simulations and our analyses are indicative of instabilities of nominally edge dislocations within fcc crystals approaching the first shear wave speed. We apply our analyses towards predicting the behaviour of dislocations within bcc crystals in the vicinity of the first shear wave speed. [ABSTRACT FROM AUTHOR]

Cross-slip is a dislocation mechanism by which screw dislocations can change their glide plane. This thermally activated mechanism is an important mechanism in plasticity and understanding the energy barrier for cross-slip is essential to construct reliable cross-slip rules in dislocation models. In this work, we employ a line tension model for cross-slip of screw dislocations in face-centred cubic (FCC) metals in order to calculate the energy barrier under Escaig stresses. The analysis shows that the activation energy is proportional to the stacking fault energy, the unstressed dissociation width and a typical length for cross-slip along the dislocation line. Linearisation of the interaction forces between the partial dislocations yields that this typical length is related to the dislocation length that bows towards constriction during cross-slip. We show that the application of Escaig stresses on both the primary and the cross-slip planes varies the typical length for cross-slip and we propose a stress-dependent closed form expression for the activation energy for cross-slip in a large range of stresses. This analysis results in a stress-dependent activation volume, corresponding to the typical volume surrounding the stressed dislocation at constriction. The expression proposed here is shown to be in agreement with previous models, and to capture qualitatively the essentials found in atomistic simulations. The activation energy function can be easily implemented in dislocation dynamics simulations, owing to its simplicity and universality. [ABSTRACT FROM PUBLISHER]

We study the distension-induced gradient capillarity in membrane bud formation. The budding process is assumed to be primarily driven by diffusion of transmembrane proteins and acting line tensions on the protein-concentrated interface. The proposed model, based on the Helfrich-type potential, is designed to accommodate inhomogeneous elastic responses of the membrane, non-uniform protein distributions over the membrane surface and, more importantly, the thickness distensions induced by bud formations in the membrane. The latter are employed via the augmented energy potential of bulk incompressibility in a weakened manner. By computing the variations of the proposed membrane energy potential, we obtained the corresponding equilibrium equation (membrane shape equation) describing the morphological transitions of the lipid membrane undergoing bud formation and the associated thickness distensions. The effects of lipid distension on the shape equation and the necessary adjustments to the accompanying boundary conditions are also derived in detail. The resulting shape equation is solved numerically for the parametric representation of the surface which has one-to-one-correspondence with the membrane surface under consideration. The proposed model successfully predicts the bud formation phenomenon on a flat lipid membrane and the associated thickness distensions of the membrane and demonstrates a smooth transition from one phase to the other (including necking domains). It is also found that the final deformed configuration is energetically favorable and therefore is stable. Finally, we show that the inhomogeneous thickness deformation on the membrane in response to transmembrane protein diffusion makes a significant contribution to the budding and necking processes of the membrane. [ABSTRACT FROM AUTHOR]