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Understanding the dynamic behavior of hydrogel formation induced by a temperature ramp is essential for the design of gel-based injectable formulation as drug-delivery vehicles. In this study, the dynamic behavior of the hydrogel formation of Pluronic F108 aqueous solutions within different heating rates was explored in both macroscopic and microscopic views. It was discovered that when the heating rate is increased, the gelation temperature window (hard gel region) shrinks and the mechanical strength of the hydrogel decreases. A given system at different heating rates would lead to different crystalline structural evolutions. The time-resolved small-angle X-ray scattering (SAXS) experiments at a heating rate of 10 °C/min disclose that the crystalline structure of micelle packing in the hydrogel exhibits a series of transitions: hexagonal close-packed (HCP) to face-centered cubic (FCC) and body-centered cubic (BCC) structures coexisting and then to the BCC structure along with the increasing temperature. For the system at equilibrium, the BCC structure exclusively dominates the system. Furthermore, the addition of a hydrophobic model drug (ibuprofen) to the F108 aqueous solution promotes hard gel formation at even lower temperatures and concentrations of F108. The SAXS results for the system with ibuprofen at a heating rate of 10 °C/min demonstrate a mixture of FCC and BCC structures coexisting over the whole gelation window compared to the BCC structure that exclusively dominates the system at equilibrium. The addition of ibuprofen would alter the structural evolution to change the delivery path of the encapsulated drug, which is significantly related to the performance of drug release.

In this study, small-angle X-ray scattering (SAXS) is successfully employed to investigate the structure of the DPPC/diC7PC disc-shaped bicelles incorporated with different amounts of C16-PEG2000-Ceramide lipids. The incorporation of the C16-PEG2000-Ceramide lipids could provide an antifouling capability to the bicelle for biomedical applications. However, traditionally it is believed that most of the incorporated PEGlylated lipids should lie in the rim of the disc-shaped bicelle. In this study, high sensitivity SAXS reveals the distribution of the added C16-PEG2000-Ceramide lipids in both the planar region and in the rim of the bicelle. The PEG brushes of C16-PEG2000-Ceramide lipids form a second shell outside the lipid headgroup shell of the bicelle. A double shell disc bicelle model is used in analyzing the SAXS data. The lipid density of C16-PEG2000-Ceramide in the rim is found to be about 1.7 times the C16-PEG2000-Ceramide lipid density in the planar region for all three C16-PEG2000-Ceramide concentrations, 1, 2, and 3 mM. Moreover, the bicelle core radius can be predicted well using the actual molecular ratio of lipids in the planar region to the lipids in the rim of the bicelles in the model calculation.

The diblock copolymer polystyrene-block-poly(N-methyl 4-vinylpyridine iodide) (PS-b-P4VPQ) with the molecular weight of PS 3.5 × 103 g/mol and P4VPQ 11.6 × 103 g/mol forms core-shell polymer micelles in aqueous solution. The cationic brush shell of the polymer micelle can be used to accommodate hydrophilic drugs and biomolecules, such as DNA, for biomedical applications. It is essential to understand how biomolecules are adsorbed within the brush layer. Here we investigated the interaction of the cationic brush of the polymer micelle with DNA by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). It is found when adding only relatively small amounts of on average 30 base pairs (bp) DNA, at 19.6 and 39.2 μM for 0.1 mM PS-b-P4VPQ, most of the polymer micelle/DNA complexes remain well dispersed. The brush layer of the polymer micelles are slightly swelled due to the adsorption of DNA within the brush layer. When the DNA concentration is increased to 58.8 μM or higher, the polymer micelle/DNA complexes form closely packed agglomerates. At high DNA concentrations, some adsorbed DNA will start to build up at the edge or surface of the brush layer which could induce aggregation of the polymer micelle/DNA complexes. This means that it is possible to prepare mostly dispersed polymer/DNA complexes by keeping the DNA concentration below the aggregation concentration. The well dispersed polymer micelle/DNA complexes are advantageous for many DNA related biomedical applications.

In this work, the microalloying approach was adopted to improve the mechanical properties of Mg-6Zn-0.5Zr alloy by co-addition of trace Cu and Ce elements. The results showed that the grain size of the Mg-6Zn-0.5Zr-0.5Cu-0.5Ce alloy was refined, and MgZnCu and Mg-Zn-Ce phases formed by the microalloying of Cu and Ce. In addition, high-density nano-scale precipitates were found in the matrix after extrusion. The alloy with Cu and Ce addition showed a basal texture with a stronger texture intensity. The yield strength, ultimate tensile strength and elongation of the as-extruded Mg-6Zn-0.5Zr-0.5Cu-0.5Ce alloy were 304 MPa, 345 MPa and 20.0%, respectively. This work demonstrated a close microstructure-strength relationship in which the refined grain size and abundant nano-scale precipitates led to an increase in the tensile yield strength of approximately 59 MPa compared with that of the Cu and Ce free alloy.

Hanatoxin (HaTx) from spider venom works as an inhibitor of Kv2.1 channels, most likely by interacting with the voltage sensor (VS). However, the way in which this water-soluble peptide modifies the gating remains poorly understood as the VS is deeply embedded within the bilayer, although it would change its position depending on the membrane potential. To determine whether HaTx can indeed bind to the VS, the depth at which HaTx penetrates into the POPC membranes was measured with neutron reflectivity. Our results successfully demonstrate that HaTx penetrates into the membrane hydrocarbon core (∼9 Å from the membrane surface), not lying on the membrane-water interface as reported for another voltage sensor toxin (VSTx). This difference in penetration depth suggests that the two toxins fix the voltage sensors at different positions with respect to the membrane normal, thereby explaining their different inhibitory effects on the channels. In particular, results from MD simulations constrained by our penetration data clearly demonstrate an appropriate orientation for HaTx to interact with the membranes, which is in line with the biochemical information derived from stopped-flow analysis through delineation of the toxin-VS binding interface.

Langmuir-Blodgett monolayers of thiolated gold nanoparticles mixed with dipalmitoylphosphatidylcholine/sodium dodecyl sulfate (DPPC/SDS) were investigated by combining the X-ray reflectivity, grazing-incident scattering, and TEM analyses to reveal the in-depth and in-plane organization and the 2D morphology of such mixed monolayers. It was found that the addition of a charged single-tail surfactant to the thiolated Au nanoparticle monolayer helps to stabilize the Au nanoparticle monolayer and to strengthen the mechanical property of the mixed monolayer film. For mixing with lipids, it was found that the thiolated gold nanoparticles could be pushed on top of the lipid monolayer when the mixed monolayer is compressed. At a typical comparable total surface area ratio of gold nanoparticle to lipid, the thiolated gold nanoparticles could form a uniform domain on top of the DPPC monolayer. When there are more thiolated gold nanoparticles than that could be supported by the lipid monolayer, domain overlapping could occur to form bilayer gold nanoparticle domains at some regions. At low total surface area ratio of thiolated gold nanoparticle to lipid, the thiolated gold nanoparticles tend to form a connected threadlike aggregation structure. Evidently, the morphology of the thiolated gold nanoparticle monolayer is highly depending on the total surface area ratio of the thiolated gold nanoparticle to lipid. SDS is found to have a dispersion power capable of dispersing the originally uniform Au-8C nanoparticle domain of the mixed Au-8C/DPPC monolayer into a foamlike structure for the mixed Au-8C/SDS/DPPC monolayer. It is evident that not only the concentration ratio but also the size and shape of the template formed by the amphiphilic molecules and their interaction with the thiolated gold nanoparticles can all have great effects on the organizational structure as well as morphology of the thiolated gold nanoparticle monolayer.

The binary P123 + F108, + F98, + F88, + F68, + F87 and + P84 systems were used to systematically explore the effect of molecular weight and hydrophobicity of Pluronic on the tendency of cooperative binding between parent copolymers and solubility of drug (ibuprofen) in these mixed Pluronic systems. Temperature-dependent co-micellization process in these systems was carefully investigated by using high sensitivity differential scanning calorimeter (HSDSC), dynamic light scattering (DLS) and small angle X-ray scattering (SAXS). All the HSDSC thermograms for these systems consistently exhibit two endothermic (micellization) peaks apart by at least 13.3 °C. It was evidenced that micelles are mainly formed by P123, the copolymer with a lower critical micelle temperature (CMT), at low temperatures. Raising temperature would dehydrate the other Pluronic with a higher CMT to be integrated into the neat P123 micelles developed at low temperatures. When the temperature is further increased beyond the second endothermic peak, the mixed micelles with a two-shell structure and characteristic corona lengths of their parent copolymers are observed to prove the existence of cooperative binding between parent copolymers. All the binary mixed Pluronic systems used in this study exhibit cooperative binding to form unimodal distribution of mixed micelles, except the P123 + F68 system. The SAXS results show that P123 + F68 system at 65 °C exhibits bimodal distribution of aggregates with coexisting of neat F68 micelles (65% in number) and P123 + F68 mixed micelles (35% in number). It is interesting to find out that P123 and F68 with distinct polypropylene oxide (PPO) moieties (i.e., a difference of 37 PO units) would exhibit very weak cooperative binding to partially form mixed micelles. Addition of ibuprofen in the P123 + F68 system would substantially enhance the cooperative binding between P123 and F68 to form bimodal distribution of aggregates with coexisting of neat F68 micelles (drops down to 30% in number) and P123 + F68 mixed micelles (increases up to 70% in number). For the systems with ibuprofen incorporated, SAXS results demonstrate that the drug is mainly encapsulated in the core of neat micelles developed at low temperatures. The solubility of ibuprofen in the 0.5 wt% P123 + 0.368 wt% P84 system is as high as 2.62 mg/ml, which is 114 times more than that in pure water at 37 °C.

We investigated the structural evolution, atomic distribution, and alloying extent of mesostructured PtRu nanoparticles electrochemically reduced on microemulsion lyotropic liquid-crystalline (MLLC) templates on addition of heptane at varied concentrations using in situ small-angle X-ray scattering and in situ X-ray diffraction, complemented with X-ray absorption spectra and a transmission electron microscope. The structural stability of the MLLC template with heptane added is much improved compared to that of the corresponding LLC without alkane. For the duration of electrochemical reduction, a structural transition occurred from hexagonal to lamellar phase of MLLC templates when the heptane concentration was more than 8 wt %. With increasing heptane concentration, atomic distribution, and alloying extent, the CO tolerance factor of PtRu nanoparticles were considerably improved. The mesostructured PtRu nanoparticles produced on MLLC-directed templates with heptane at a concentration of 8 wt % show a stru...

We demonstrate that the lamella-forming polystyrene-block-poly(N-methyl-4-vinylpyridinium iodine) (PS-b-P4VPQ), with similar sizes of the PS and P4VPQ blocks, can be dispersed in the aqueous solutions by forming lipid/PS-b-P4VPQ multilamellae. Using small-angle neutron scattering (SANS) and 1,2-dipalmitoyl-d62-sn-glycero-3-phosphocholine (d62-DPPC) in D2O, a broad correlation peak is found in the scattering profile that signifies the formation of the loosely ordered d62-DPPC/PS-b-P4VPQ multilamellae. The thicknesses of the hydrophobic and hydrophilic layers of the d62-DPPC/PS-b-P4VPQ multilamellae are close to the PS layer and the condensed brush layer thicknesses as determined from previous neutron reflectometry studies on the PS-b-P4VPQ monolayer at the air-water interface. Such well-dispersed d62-DPPC/PS-b-P4VPQ multilamellae are capable of forming multilamellae with DNA in aqueous solution. It is found that the encapsulation of DNA in the hydrophilic layer of the d62-DPPC/PS-b-P4VPQ multilamellae slightly increases the thickness of the hydrophilic layer. Adding CaCl2 can enhance the DNA adsorption in the hydrophilic brush layer, and it is similar to that observed in the neutron reflectometry study of the DNA adsorption by the PS-b-P4VPQ monolayer.

The atomic structure relocation of a NiOcore–Ptshell nanocatalyst (NC) in direct methanol fuel cells for a long-term work cycle is quantitatively investigated by performing both X-ray absorption spectroscopy and electrochemical potential sweeping analyses. We found that Pt atoms in this metal-to-metal oxide junction NC tend to dissolute on reducing the domain size in a long-term DMFC work cycle in the condition of Pt > 30 at%. On the other hand, with Pt < 30%, Pt atoms are rearranged into a thin homoatomic shell at the NiO surface. Such an atomic reconfiguration is controlled by competition between dissolution and relocation of Pt/Ni atoms at varying facets. For the optimum case (Pt < 30%), the current density and the output power density of DMFC are doubled by using NiO–Ptshell NC at the anode as compared to that using a PtRu alloy.

This research demonstrated that the methanol oxidation reaction triggers the protonation corrosion on the multi-walled carbon nanotube supported bimetallic nanocatalysts (NCs) in different geometrical configurations. Such corrosion pathways are confined by the geometrical configuration of the heterogeneous interfaces at the bimetallic oxide nanoparticles. In bimetallic alloyed NCs, the platinum (Pt) and ruthenium (Ru) domains were exposed simultaneously to the redox environment, therefore, the geometrical confinement on the atomic restructure is weak. This leads to substantial dissolution followed by the regrowth of hydrophilic components in redox conditions. For core–shell NCs, the shell crystal would prevent the core from direct contact with the redox environments. The heteroatomic junction forms ordered Pt atomic stacking at the ruthenium oxide crystallite. Such conformation confinement enhanced the Pt to Ru charge donation, thus the CO tolerance factor was also enhanced by more than two orders of magnitude when compared to the module durability of the direct methanol fuel cell compared to that of PtRu alloy.

Time-resolved small-angle X-ray scattering was applied to study charged lipid exchange between oppositely charged disc-shaped bicelles. The exchange of charged lipids gradually reduces the surface charge density and weakens the electrostatic attraction between the oppositely charged bicelles which form alternately stacked aggregates upon mixing. Initially, at a high surface charge density with almost no free water layer between the stacked bicelles, fast exchange kinetics dominate the exchange process. At a later stage with a lower surface charge density and a larger water gap between the stacked bicelles, slow exchange kinetics take over. The fast exchange kinetics are correlated with the close contact of the bicelles when there is almost no free water layer between the tightly bound bicelles with a charged lipid exchange time constant as short as 20-40 min. When the water gap becomes large enough to have a free water layer between the stacked bicelles, the fast lipid exchange kinetics are taken over by slow lipid exchange kinetics with time constants around 200-300 min, which are comparable to the typical time constant of lipid exchange between vesicles in aqueous solution. These two kinds of exchange mode fit well with the lipid exchange models of transient hemifusion for the fast mode and monomer exchange for the slow mode.

Metallic Ag nanowires coated with a TiO2 nanolayer (AgNWs@TiO2) were employed as electron conductors in the mesoporous photoanodes (developed by TiO2 nanoparticles, P25) of dye-sensitized solar cells (DSSCs). Our results demonstrate that the AgNWs@TiO2 (in an optimized content of 3 wt% in the photoanode) improved the energy conversion efficiency (η) of the DSSC from 4.68 to 5.31% compared to the DSSC without AgNWs@TiO2 (pure P25). Such an improvement could be mainly attributed to the reduced TiO2/dye/electrolyte interfacial charge transfer impedance. To our surprise, the surface plasmon resonance (SPR) and light scattering effects of the nanowires were found to substantially boost the incident photon-to-electron conversion efficiency (IPCE) of such DSSCs. Regardless of the assembly techniques, our results demonstrate the possibilities of developing the photoanode with reduced interfacial impedance and superior light harvesting capability compared to the existing photoanodes in similar configurations by appropriately adjusting the AgNWs@TiO2 content in the photoanode with P25 based composites.

The growth of platinum shell crystals on the heterogeneous facets of ruthenium metal nanocrystals was investigated via in situ small angle X-ray scattering analysis. Our results illustrated that the pathway of shell crystal growth is mainly affected by controlling the incubation time prior to the thermal reduction of Pt ions by polyol radicals. For short incubation times, the shell crystal grows on the radial facets and the face facets of the nano-cylinder core via heterogeneous nucleation and crystal growth with and without assistance by transmetallation, respectively. On the other hand, severe chemical etching was observed prior to shell crystal growth after incubation for 2 hours. Consequently, the shell structure is formed from the nucleation of a PtRu alloy followed by the growth of Pt crystals. In both cases, dynamic restructuring at the core–shell interface was observed upon deposition of the shell crystal. These results enable the development of core–shell crystallites in expected configurations and with tuneable atomic structures.

Thermally stable and porous RuO 2 · x H 2 O with superior rate-retention capability is prepared by the H 2 O 2 -oxidative precipitation method modified with the cetyltrimethylammonium bromide (CTAB) template. The specific capacitance and rate-retention of RuO 2 · x H 2 O are considerably enhanced by the CTAB modification and annealing at 200 °C because of extremely localized crystallization and pore opening of slightly sintered RuO 2 · x H 2 O nanoparticles trapped with CTAB. This unique structure, confirmed by the X-ray absorption spectroscopic (XAS), Raman spectroscopic, and transmission electron microscopic (TEM) analyses, favors the utilization of RuO 2 · x H 2 O nanocrystals and increases the electrolyte accessibility in comparing with RuO 2 · x H 2 O without CTAB modification. The preferential orientation growth along the {101} facet of RuO 2 nanocrystals in some local regions is acquired by the CTAB modification and annealing in air at temperatures ≥350 °C. Such preferential orientation growth of RuO 2 crystallites is attributable to the oxidation of trapped surfactants during the thermal annealing process, which adsorb on the high surface energy planes of RuO 2 .

In this study, a porous TiO 2 thin film was modified with a robust sol–gel process to form interconnected nanoparticle networks for facilitating charge transfer in a dye-sensitized solar cell. Compared to the conventionally prepared photoanode using only P25 TiO 2 nanoparticles, such a unique processing method could reduce the interfacial impedance by ~ 18% (from 27.6 Ω to 22.5 Ω) by forming interparticle-bindings between the P25 TiO 2 nanoparticles with the sol–gel TiO 2 . Such a processing method could improve the photocurrent density by ~ 30% (from 10.07 mA/cm 2 to 13.07 mA/cm 2 ) and consequently it results in a ~ 20% photovoltaic efficiency improvement of dye-sensitized solar cell (from 4.83% to 5.81%). In addition to the photovoltaic performance enhancement, such a facile method with reduced processing time and energy consumption provides the possibility of developing high performance and cost-effective dye-sensitized solar cells.

We investigate the Rucore-Ptshell nanoparticles (NPs) with near-monolayer thick shell atoms as the electrocatalysts at anode in the direct methanol fuel cell (DMFC). The results of X-ray diffraction indicate that its crystal structure experienced a compressive strain in Pt shell region. The shell thickness of Rucore-Ptshell NPs was determined to be 1.5 atomic layers by small-angle X-ray scattering by using a core–shell scattering model, and the surface atomic morphology was illustrated via high-resolution transmission electron microscopy (HRTEM). Compared with the Pt NPs, the power density of DMFC with Rucore-Ptshell NPs was improved by ∼450% (from 17.1 to 92.8 mW cm–2 mg–1), and the open-circuit voltage was improved by 0.18 V (from 0.49 to 0.67 V). Our results fulfill the development of cost-effective DMFC with outstanding performance.

We demonstrate the significance of ions with an ordered arrangement for enhancing the electron injection in polymer light-emitting diodes (PLEDs) and the electron extraction in polymer solar cells (PSCs) by using tetraoctylammonium bromide (TOAB) as a model compound. The spin-coated films of TOAB are prepared on the active layers of both PLEDs and PSCs without any annealing (TOAB-No) as well as with annealing at 60 °C (TOAB-60) and 100 °C (TOAB-100). Subsequently, they are investigated by atomic force microscopy (AFM) and synchrotron X-ray diffraction (XRD) as well as simultaneously employed as the interfacial layers in PLEDs and PSCs. The AFM results show that the active layers are well covered with TOAB-No and TOAB-100, but poorly covered with TOAB-60 due to the formation of large islands. The XRD results show that TOAB-No and TOAB-60 are polycrystalline with the (002) lattice planes parallel to the surface of the active layers while TOAB-100 is amorphous. Of note, the electron injection in PLEDs and the electron extraction in PSCs are significantly enhanced using TOAB-No and TOAB-60, but both are worsened using TOAB-100. Evidently the enhanced electron injection/extraction is mainly attributed to the ordered arrangement of ions in the TOAB crystals. This study indicates that with an ordered arrangement of ions, all ionic compounds should be excellent for enhancing the electron injection/extraction in polymer optoelectronic devices.

This study investigates biogeochemical reductive release of arsenate from beudantite into solution in a crater area in northern Taiwan, using a combination of X-ray absorption near-edge structure (XANES) and atomic absorption spectrometry. Total arsenic (As) concentrations in the soil were more than 200 mg/kg. Over four months of laboratory experiments, less than 0.8% As was released into solution after reduction experiments. The 71% to 83% As was chemically reduced into arsenite (As(III)) and partially weathering into the soluble phase. The kinetic dissolution and re-precipitation of As, Fe, Pb and sulfate in this area of paddy soils merits further study.

We demonstrated that the reactivity, electrochemically active area (ECSA), and long-term structural stability of Pt-based core–shell nanoparticles (NPs) under the methanol oxidation reaction (MOR) can be controlled by the crystal structure and the chemical composition of the core. This approach is inspired by the structural relaxation of shell Pt atoms on two types of crystalline cores (e.g., Ru and Co) due to the differences in surface free energy between facets. Due to the isotropic facet energy of the Co cores, the initial formation of the Pt shell is under kinetic control when the shell thickness is less than two atomic layers (∼3 A). After the surface layer is formed, the subsequent growth of the Pt shell atoms is under surface diffusion control. For Ru core crystallites with significantly different facet energies, the NPs are disk-like shaped, indicating that the shell atoms preferentially deposit onto the radial edges in the absence of nucleation barriers. In this case, the ECSA of the Rucore–Ptshell NPs is 2.23-fold higher than that of the Cocore–Ptshell NPs, which is promising in the electrocatalytic oxidation of methanol and H2O2 for the applications of fuel cells and sensors, respectively.

The activity of core–shell nanoparticles (NCs) in electrooxidation of methanol (MOR) was found to be dependent on the crystalline structure of the core and the lattice strain at the core–shell interface. Ru-core and Pt-shell NCs delivered 6.1-fold peak MOR current density at −135 mV than Pt NCs, while the Co-core and Pt-shell NCs showed a 1.4-fold peak MOR current density at 280 mV. The current density is improved by the compressive lattice strain of the surface that is caused by the lattice mismatch between the Pt shell and the Ru core. For Co-core NCs, the enhancement results from the ligand effect at surface Pt sites. In addition, the Ru-core NCs maintained a steady current density of 0.11 mA cm–2 at 500 mV in a half-cell system for 2 h, which is 100-fold higher than that of Pt NCs and Co-core NCs. These results provide mechanistic information for the development of fuel cell catalysts along with reduced Pt utilization and programmable electrochemical performance.

Real-time in situ ellipsometry was used to investigate the etching of SiO2/silicon wafers with a high concentration of Cl2. We monitored the temporal trajectory of the ellipsometric parameter Δ and then selected several points for ex situ study using atomic force microscopy (AFM). There was a clearly observable transition period in the trajectory near the endpoint of the SiO2/Si interface. We studied the relationship between the ellipsometric parameter Δ and the same point in the AFM ex situ measurements. Three stages, thin film, the interface layer, and the substrate, were analyzed in this work.

This study develops a simple surface modification process for modifying the MWCNT surface by thiolation reaction after the conventional nitric acid treatment for strong interface attachment of Pt NPs and improved dispersion onto MWCNTs. The thiolated MWCNTs (Pt/MWCNTs) showed significant improvement of methanol electro-oxidation activity compared with that treated only by nitric acid solution. The prepared electrode with thiolated MWCNTs was used as the cathode for assembling MEA for DMFC single-cell applications. Testing results indicate that the thiolated MWCNT cathode can improve the power density of MEA by more than 300% (from 4.6 to 20.6 m W cm -2 ) compared with that treated only by conventional nitric acid reactions. The dual-step modification process for MWCNT surface treatment showed significant improvement over the convention nitric acid treatment and can be successfully used in DMFC applications.

We have previously synthesized Cu/Pd nanoparticles with a citric complexing agent, demonstrating well the suspension and high catalytic ability of electroless copper deposition. Herein, we report the in situ investigation of the synthesis of Cu/Pd nanoparticles with a citric complexing agent by X-ray absorption near-edge structure (XANES). By characterizing the XANES spectra of Cu and Pd upon the stepwise addition of an alkaline solution, the reaction mechanism of Cu as well as Pd complexing ions was elucidated. Slow reduction of Pd ions and fast reduction of Cu ions induced by zerovalent Pd are found in XANES spectra. A three-stage formation mechanism of Cu/Pd nanoparticles was proposed in which a Pd reduction initial stage, a Cu-dominated reduction middle stage, and a Pd-dominated reduction final stage were indicated. As a result, a Pd-rich outer shell formed on the surface of synthesized Cu/Pd particles in the final stage. In summary, the formation mechanism and the Pd-rich outer shell structure of syn...

Using neutron reflectivity with contrast variation, X-ray reflectivity, and grazing incident small-angle X-ray scattering (GISAXS), we have characterized the in-depth and in-plane structural characteristics of the Langmuir and Langmuir-Blodgett (LB) films formed by a novel lecithin C60-derivative, FPTL, of three phospholipids jointly bonded on one single olefinic moiety of a C60 cage. Based on the neutron reflectivity measured, we have proposed a monolayer structure, with the C60 cages of FPTL lifted into the air and hydrophilic phospholipid heads immersed in water, for the FPTL Langmuir layer formed on water. On the other hand, the LB film of FPTL prepared on mica exhibits clear Kiessig fringes in the X-ray reflectivity profile, indicating a 27 angstroms monolayer film with less molecular orientation. With GISAXS, we have extracted an in-plane correlation length of about 210 A for a possible in-plane aggregation of C60 of FPTL in the LB monolayer. We have also demonstrated the highly ordered monolayer structures of a lecithin lipid, in elucidating the positive effect of the attached functional group-phospholipids on the monolayer formation of the lecithin C60-derivative.

The β-amyloid peptide (Aβ) (1–40) is one of the major components that form Alzheimer's amyloid deposits. Studies of the membrane insertion of amyloid showed that amyloid is surface active and can insert into lipid monolayers [Ji et al. (2002). Biochemistry (Moscow), 67, 1283–1288; Ege & Lee (2004). Biophys. J. 87, 1732–1740]. The interaction between the peptide and a lipid monolayer or bilayer is critical to the understanding of the formation of amyloid peptide deposits on the membrane. In this paper, we have studied the structural transition of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) multibilayers with the insertion of amyloid peptide 1–40 by grazing-incidence small-angle X-ray scattering at different bilayer hydration levels (changing the relatively humidity). We mixed the DPPC and amyloid peptide in an organic solvent at a 10 to 1 weight ratio, then cast it onto a silicon wafer to form the mixed lipid multibilayer film. In this study of the pure DPPC multibilayer film and the DPPC multibilayer film inserted with amyloid peptide, it was found that the hydration process was bimodal with a better-hydrated top layer and a less-hydrated bottom layer. The gel-to-ripple phase transition suffers a strong confinement effect due to the presence of the solid substrate. With the insertion of the amyloid peptide, the ripple phase of the membrane bilayers was suppressed at high humidity and the whole film can be swollen more uniformly at lower incubation time than the pure DPPC film supported on a silicon wafer. This means water vapor can penetrate more easily into the DPPC bilayers inserted with Aβ than into the pure DPPC bilayers. Amyloid peptides were found to form clusters in the bilayer and possess in-plane correlation. From analyzing the diffuse scattering around the Bragg peak in the lateral direction, the amyloid peptides are found to form clusters in the bilayer with a radius of about 9 nm. It is also estimated that the number of Aβ molecules in one cluster is about 12 and on average each Aβ molecule occupies an interface area of about 22 nm2. As the relative humidity exceeds about 94%, the Aβ clusters seem to develop an ordered structure with a spacing of about 300 A.

Small-angle X-ray scattering was used to characterize the size and aggregation behavior of the Pt nanoparticles synthesized by the polyol process and the unusual poly(N-vinyl-2-pyrrolidone) (PVP) reduction. With formaldehyde (HCHO) as the reduction agent, the Pt nanoparticles synthesized in aqueous solutions with a high PVP/PtCl4 weight ratio were characterized by short rods with a 70% polydispersity in rod length. The size and size distribution of the rod-like Pt nanoparticles (3 nm in rod length and 2 nm in rod diameter) are consistent with the corresponding transmission electron microscopy image. With a comparable PVP/PtCl4 weight ratio in the aqueous solution containing HCHO, the high number density of reduced Pt nanoparticles led to a fractal-like aggregation with a fractal dimension of 2.1 and a correlation length of ~30 nm. We also demonstrated that Pt nanoparticles can be synthesized by PVP reduction at 323 K without HCHO. The particle size and the clustering behavior of the Pt nanoparticles reduced by PVP are closely related to the PVP concentration in the solution. Both the Pt nanoparticles synthesized in the commonly used polyol process and the unusual PVP reduction form fractal-like clusters via the PVP–metal nanoparticle association when the number density of the Pt nanoparticles in the solutions is high.

Atomic-scale gold clusters were intercalated at the inter-facet corner sites of Pt-shell Ru-core nanocatalysts with near-monolayer shell thickness. We demonstrated that these unique clusters could serve as a drain of valence electrons in the kink region of the core–shell heterojunction. As jointly revealed by density functional theory calculations and valence band spectra, these Au clusters extract core-level electrons to the valence band. They prevent corrosion due to protonation and enhance the tolerance of CO by increasing the electronegativity at the outermost surface of the NCs during the methanol oxidation reaction (MOR). In these circumstances, the retained current density of Pt-shell Ru-core NCs is doubled in a long-term (2 hours) MOR at a fixed voltage (0.5 V vs. SCE) by intercalating these sub-nanometer gold clusters. Such novel structural confinement provides a possible strategy for developing direct-methanol fuel cell (DMFC) modules with high power and stability.

A SWAXS (small- and wide-angle X-ray scattering) instrument was recently installed at the wiggler beamline BL17B3 of the National Synchrotron Radiation Research Center (NSRRC), Taiwan. The instrument, which is designed for studies of static and dynamic nanostructures and correlations between the nano (ormeso) structure (SAXS) and crystalline structure (WAXS), provides a flux of 1010–1011photon s−1at the sample at energies between 5 and 14 keV. With a SAXS area detector and a WAXS linear detector connected to two data acquisition systems operated in master–slave mode, the instrument allows one to perform time-resolved as well as anomalous scattering measurements. Data reduction algorithms have been developed for rapid processing of the large SWAXS data sets collected during time-resolved measurements. The performance of the instrument is illustrated by examples taken from different classes of ongoing projects: (i) time-resolved SAXS/WAXS/differential scanning calorimetry (DSC) with a time resolution of 10 s on a semicrystalline poly(hexamethylene terephthalate) sample, (ii) anomalous SAXS/WAXS measurements on a nanoparticulate PtRu catalyst, and (iii) grazing-incidence SAXS of a monolayer of oriented semiconductor quantum wires, and humidity-controlled ordering of Alamethicin peptides embedded in an oriented lipid membrane.

We have studied DNA adsorption on mixed DPPC/DC-Chol monolayers. Solid supported mixed monolayers on silicon wafers were prepared using Langmuir–Blodgett (LB) dipping technique. Neutron and X-ray reflectivity measurements were used to characterize these LB monofilms. For LB monofilms with DNA adsorption, the reflectivity data of the DPPC/DNA film are very close to that from the DPPC film, which indicates only minor DNA adsorption on the pure DPPC monolayer. Increasing the percentage of DC-Chol, film thickness increases. The DC-Chol/DNA film is thicker than the pure DC-Chol film (film thickness 18 A) by about 9 A due to the presence of adsorbed DNA. A model is presented to explain the structure of the lipid/DNA film.

A synthetic charged lipid, DC-Chol (3β-[N-(dimethylaminoethane)-carbamoyl]-cholesterol), was used to mix with the DPPC (1,2-dipalmitoyl-sn-glycero-3-phosphocholine) to form monolayers at the air–liquid interface. The mixed DPPC/DC-Chol monolayer at the air–water interface was studied by measuring the surface pressure versus molecular area isotherms and BAM. The pressure–area isotherm shows that typical plateau of DPPC disappears by adding DC-Chol more than 30%. It was also found that the DPPC/DC-Chol system has only one minimum excess area point at XDC-Chol = 0.2. The absence of the minimum excess area point at higher DC-Chol mixing ratio should be due to the charge interaction of DC-Chol. It was observed by BAM that the domains formed in the plateau region of the isotherm become smaller by adding small amounts of DC-Chol. These domains as well as the plateau region disappear at XDC-Chol ≧ 0.3. The characteristics of the mixed monolayer seems to be dominated by the charged DC-Chol at XDC-Chol ≧ 0.3. The results of X-ray reflectivity measurements of the mixed DPPC-d62/DC-Chol LB monolayer supported on silicon wafer show that the DC-Chol molecules are positioned in the DPPC-d62 hydrophobic layer.

Nonisothermal crystallizations of polycaprolactone (PCL) in the presence of poly(vinyl chloride) (PVC) at a cooling rate of 0.5 °C/min from 90 to 30 °C under supercritical CO2 at a constant pressure 304 atm were investigated. DSC and SAXS data found that the nonisothermal crystallizations of the PCL/PVC blends under supercritical CO2 resulted in decrease in thickness of the crystalline layers in the lamellar stacks. These nonisothermal supercritical CO2 treatments also generated a morphological heterogeneity with size (13.8 nm for pure PCL) larger than the long period (12.1 nm) of the lamellar stacks. The size of this heterogeneity was slightly enhanced from 13.8 nm for pure PCL to 15.2 and 16.3 nm for the blends containing 10 and 25 wt % PVC, respectively.

Structural characteristics of optical quality poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phen- ylenevinylene) (MEH-PPV) films drop-cast from toluene solutions have been examined by use of wide- angle (WAXS) and small-angle X-ray scattering (SAXS) as well as field-emission scanning electron microscopy. For the as-cast film SAXS and WAXS patterns clearly suggest existence of nanodomains of mesomorphic order. Under grazing incidence, both SAXS and WAXS patterns of the as-cast film exhibit impressive uniaxial symmetry with strong scattering along the film normal; however, the corresponding normal-incidence patterns are circularly isotropic, implying in-plane random orientation. A structural model consisting of preferentially uniaxial-oriented nanodomains and disordered matrix is therefore proposed for the as-cast film. Annealing at 210 °C results in disorientation of nanodomains: this decrease in structural asymmetry upon heat treatment correlates well with concomitant changes in charge transport behavior determined from time-of-flight measurements, manifesting dramatically decreased charge mobility as well as transition from nondispersive to dispersive modes.

We have studied the structure and phase transition characteristics of the fullerenes (C 60 )-embedded lipid bilayers. With small-angle neutron scattering (SANS), we have observed a degradation of bilayer ordering and a suppression effect on the phase transitions of the host vesicle bilayers of dipalmitoylphosphatidylcholine (DPPC), due to the embedment of fullerenes. The fullerene-embedded lipid system with substrate-oriented bilayers is also investigated using X-ray reflectivity and grazing incident small-angle X-ray scattering (GISAXS). In the depth direction, the multilamellar peaks observed in the X-ray reflectivity profile for the oriented DPPC/C 60 bilayers reveal a larger head-to-head distance D HH of 50.6 A and a bilayer spacing D of 59.8 A, compared to the D HH =47.7 A and D =59.5 A for a pure DPPC membrane measured at the same conditions. Furthermore, the lipid head layers and water layers in the extracted electron density profile for the complex system are highly smeared, implying a fluctuating or corrugated structure in this zone. Correspondingly, GISAXS for the oriented DPPC/C 60 membrane reveals stronger diffuse scatterings along the membrane plane than that for the pure DPPC system, indicating a higher in-plane correlation associated with the embedded fullerenes.

The structures of Nafion membranes prepared by solutions casting from low aliphatic alcohols/water mixture solvents and N,N′-dimethyl formamide (DMF) solvent were investigated using differential scanning calorimeter and small angle X-ray scattering. The aggregation behavior of Nafion molecules in the casting solutions was also investigated using dynamic light scattering. We show that the morphology of membranes was strongly influenced by the conformations of Nafion molecules in the solutions. In aliphatic alcohol/water mixture solvents, which have a worse compatibility with Nafion backbones, the Nafion molecules aggregate and form fringed rod-like structures. These primary rod-like structures then aggregate again through fringed side chains to form secondary ionic aggregations. In DMF solvent, owing to its better compatibility with Nafion backbones, less Nafion molecules aggregate. The high degree of Nafion molecular aggregations in aliphatic alcohol/water mixture solvents leads to a high degree of hydrophobic and hydrophilic phase separation for membranes prepared by casting from Nafion/aliphatic alcohol/water solutions. However, the lower degree of molecular aggregations in DMF solvent results in a lower degree of hydrophobic and hydrophilic phase separation for membranes prepared by casting from Nafion/DMF solution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3044–3057, 2005

Liposome consisting of a single zwitterionic lipid as the potential vector for gene therapy has been reported recently; however, whether polyanionic DNA can bind directly with zwitterionic lipid without the aid of multivalent salt still remains unresolved. In this study, we reveal the aggregation of zwitterionic oligolamellar liposomes composed of 1,2-di(cis-9-octadecenoyl)-sn-glycero-3-phosphocholine induced by DNA without the presence of multivalent salt. Our results demonstrate that only a small fraction (

Polyanionic DNA can bind electrostatically with cationic lipid to form the complex exhibiting rich self-assembled structures at various length scales. This class of bioassembly has been considered as a nonviral gene delivery system for gene therapy and as a template for nanostructure construction. The present study reports the self-assembled structure of the binary complex of DNA with a cationic lipid, cholesteryl 3β-N-((dimethylamino)ethyl)carbamate (DC-Chol), in the presence of excess water. Neat DC-Chol self-assembled into cylindrical micelles in aqueous media. These micelles aggregated and fused into multilamellar condensates or vesicles upon complexation with DNA, and the DNA chains confined between the lipid bilayers formed closely packed arrays irrespective of the overall lipid-to-base pair molar ratio. The complexation was found to be a highly cooperative process, where the complexes with nearly 1:1 stoichiometry were formed even when DNA was in excess of DC-Chol in terms of the overall ionic char...

A multiple harmonic intensity ratio technique is proposed for calibrating the modulation amplitude (Δ0) of a photoelastic modulator (PEM). A data acquisition system is utilized to investigate the frequency response of this technique. Δ0 determined by this technique is independent of frequency, which is proved using the reflection and transmission setups. In addition to confirm our calibration using the digitized oscilloscope waveform, we also obtain a set of ellipsometric parameters under various values of Δ0 before and after calibration. We also introduce a correction factor to correct the effect caused by the shift of the modulation amplitude in the process of etching. An optical thick film is used to calibrate Δ0 using PEM ellipsometry, and its refractive index and extinction coefficient are also obtained in etching. Finally, we suggest the use of the traces of the ellipsometric parameters under various thicknesses for monitoring instead of calculating the thickness in real time.

Lamellar morphologies of melt-crystallized blends of syndiotactic polystyrene (sPS, weight-average molecular weight M w =200 k ) and atactic polystyrene (aPS, Mw=100k) have been investigated using small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). sPS/aPS blends with various compositions were prepared and crystallized isothermally at 250 °C prior to morphological studies. Due to the proximity in the densities of the crystal and amorphous phases, a weak SAXS reflection associated with lamellar microstructure was obtained at room temperature. In addition, strong diffuse scattering at low scattering vectors was evidently observed and its appearance may obscure the intensity maximum associated with the lamellar features, leading to the difficulties in determining the microstructure of the blends. To enhance the density contrast, SAXS intensities at an elevated temperature of 150 °C were measured as well to deduce the morphological results with better precision. Based on the Debye–Bueche theory, the intensities of the diffuse scattering were estimated and subtracted from the observed intensities to obtain the scattering contribution exclusively from the lamellar microstructure. Morphological parameters of the sPS/aPS blends were derived from the one-dimensional correlation function. On addition of aPS, no significant changes in the lamellar thickness have been found and the derived lamellar thicknesses are in good agreement with TEM measurements. Segregation of rejected aPS components during sPS crystallization was evidently observed from TEM images which showed aPS pockets located between sPS lamellar stacks and distributed uniformly in the bulk samples, leading to the interfibrillar segregation.

The effect of supercritical CO2 on the morphological structure of compatible crystalline/amorphous poly(ethylene oxide) (PEO)/poly(methyl methacrylate)(PMMA) blends was investigated by means of small angle X-ray scattering (SAXS) with the measurement of absolute scattering intensity. The morphological structure of PEO/PMMA exhibited a considerable change upon CO2 treatment as demonstrated by the drastic increase of scattering intensity, or the enhancement of electron density contrast between the crystalline and amorphous layers in the lamellar stacks, resulting from the swelling of amorphous PEO via the incorporation of CO2 into the interlamellar (IL) regions. Upon CO2 treatment, both the crystal and amorphous layer thickness (lc and la, respectively) were increased with the extents depending on the blend composition. The increasing of la upon CO2 treatment was decreased with increasing PMMA content, suggesting that PEO was much easier to be swollen by CO2 than PMMA. Compared with the increase of la, the increase of lc was much more significant and was attributed to the occurrence of melting and recrystallization during CO2 treatment that led to thicker PEO crystals caused by an increased crystal surface free energy. The measured electron density contrast revealed that the distance of segregation in the PEO/PMMA blends involved the extralamellar segregation before CO2 treatments and the swelling of IL region dominated the drastic increase of scattering intensity after CO2 treatments. The finding of extralamellar morphology was consistent with the magnitude of volume fraction of lamellar stacks in the blends. The CO2 treatment could increase the distance of segregation for neat PEO and PEO-rich blends. The lamellar size distribution appeared to be broader and the lamellar stacks more disorganized for the blends after CO2 treatments according to SAXS one-dimensional correlation function profiles.

Crystallization in the microdomains of crystalline−amorphous diblock copolymers may induce domain coalescence when the crystallization temperature lies above the Tg of the amorphous matrix. In this study, the perturbation of microdomain structure driven by isothermal crystallization and postannealing in a poly(ethylene oxide)-block-poly(1,4-butadiene) (PEO-b-PB) and PEO-b-PB/PB homopolymer (h-PB) blends consisting of spherical PEO domains in the melt state is systematically investigated to reveal whether the presence of homopolymer in the amorphous matrix would hinder or facilitate the microdomain coalescence driven by the crystallization. Three samples with nearly the same volume fraction and length of PEO block are adopted for the study; the first is an asymmetric PEO-b-PB that contains no h-PB, the second is a blend containing 12 wt % of h-PB, and the third is a blend consisting of 63 wt % of h-PB. Characterization of the domain structure after isothermal crystallization and postannealing treatment by ...

While the aging temperature is increased to low undercooling, 180 °C for Al–9.7 at.% Li alloy, the transitions of both the coarsening mechanism and the size distribution of δ′ precipitates in Al–Li alloy are found and studied using small-angle X-ray scattering (SAXS) technique. A modified precipitation mechanism considering this transition is explored with respect to both the determined precipitate size distribution and the growth rate constant. Additionally, a more adequate method is established for estimating the growth rate constant as a function of aging temperature and Li concentration, and those results are compared with corresponding measurement results.

We have studied the interactions of a lipophilic C60-derivative, synthesized recently for potential biomedical applications, with phospholipid monolayers and bilayers. The results of surface pressure–area isotherms, atomic force microscopic images, and neutron and X-ray scattering show consistently that the lipophilic C60 can intercalate into monolayers as well as vesicle bilayers of the phospholipids studied. In general, the lipophilic C60 can incorporate into the lipid membranes better in the liquid crystal phase, and modify the bending and compression modulus of the host lipid membranes significantly.

Monolayers of a lipophilic C 60-derivative (FPTL) mixed in dipalmitoyl-phosphatidyl-choline (DPPC) have been studied by the Langmuir film balance technique and Brewster angle microscopy. Previous X-ray scattering studies showed that the FPTL molecules intercalated into the DPPC monolayers and modified the bending and compression modulus of the host DPPC membranes. Combined study of surface pressure–area isotherms and Brewster angle microscopy measurements clearly established that the liquid-condensed domain structures are strongly influenced by an addition of the fullerene bearing lipid molecules, where it caused smaller liquid-condensed domain structures.

We studied the self-assembly behavior in the bulk complexes of poly(ethylene oxide) (PEO) with an amphiphilic dodecylbenzenesulfonic acid (DBSA) formed through hydrogen bonding. In the hydrate state, PEO−DBSA complexes self-organized into a lamellar morphology consisting of alternating stacks of polar and nonpolar layers. The interlamellar distance increased with decreasing binding fraction of DBSA due to increasing inclusion of unbound monomer units into the polar layers. In the disordered state the comblike structure persisted and a “correlation hole” peak was present in the corresponding small-angle X-ray scattering (SAXS) profile. Complexation with PEO greatly promoted the thermal stability of the mesophase and the dynamics of mesophase formation as compared with those in pure DBSA. The faster mesophase formation in the complexes was proposed to stem from the higher isotropization temperature as well as the existence of comblike structure in the disordered melt.

Lamellar morphology and thickness of syndiotactic polystyrene (sPS) samples melt-crystallized at various temperatures were probed using transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS). In addition, the melting temperature and enthalpy of the crystallized samples were characterized with differential scanning calorimetry. Under appropriate thermal treatments, all the samples investigated in this study were crystallized into β′ crystal modification, as revealed by wide-angle X-ray diffraction. From the SAXS intensity profiles, a scattering peak (or shoulder) associated with lamellar features as well as the presence of anomalous scattering at the zero-scattering vector were evidently observed. The peculiar zero-angle scattering was successfully described by the Debye–Bueche model, and subtraction of its contribution from the raw intensity profiles was carried out to deduce the intensity profile merely associated with the lamellar feature. The lamellar thickness obtained from Lorentz-corrected intensity profiles in this manner agrees with that measured from the TEM images, provided that the two-phase model is applied. On the basis of the Gibbs–Thomson equation, the modest estimations of equilibrium melting temperature and the surface free energy of the fold lamellar surface are 292.7 ± 2.7 °C and 20.2 ± 2.6 erg/cm2, respectively, when lamellar thicknesses measured by TEM are applied. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1626–1636, 2002

Solvent transport in poly(ethylene terephthalate) (PET) and related phase transformation were investigated. The data of mass sorption were analyzed according to Harmon's model for Case I (Fickian), Case II (swelling), and anomalous transport. This transport process in PET is accompanied by the induced crystallization of the original amorphous state. The transformation was examined by wide-angle X-ray scattering, small-angle X-ray scattering, differential scanning calorimetry, and Fourier transform infrared spectroscopy. During this process, the matrix is under a strain state that causes different kinetic paths of crystallization as compared with that by thermal annealing. This state of strain assists the development of the solvent-induced crystallization. The model regarding crystallization was proposed in terms of the study of long period L, the crystal thickness lc, and the thickness of amorphous layer la obtained from the one-dimensional correlation function and interface distribution function. Different kinetic paths were discovered for different crystallization processes. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1444–1453, 2002