Surface Segregation in Miscible Blends of Polystyrene and Poly(vinylmethyl ether): Comparison of Theory and Experiment

The effect of the interplay between bulk and surface free energy terms on surface segregation in miscible blends is probed by comparing angle-dependent x-ray photoelectron spectroscopy (ADXPS) measurements for polystyrene/polyvinylmethylether (PS/PVME) blends of with those for perdeuteropolystyrene/polyvinylmethylether (dPS/PVME) blends. The magnitudes of the bulk interaction parameters for the two systems differ markedly while the surface interactions are essentially identical. Experimental concentration depth profiles are almost identical for the two systems indicating that their surface properties are little affected by bulk interactions and dominated by surface energy effects.These data and previous data from our group are compared to the predictions of the square gradient theory developed by Schmidt and Binder in order to gain a more quantitative understanding of the factors that control surface segregation in miscible blends. While there is general qualitative agreement between theory and experiment, predicted surface compositions fall significantly below experimental values and predicted composition depth profiles decay more gradually than what is observed experimentally, especially for low PVME contents. The use of the more appropriate Sanchez-Lacombe-Balazs equation of state does not yield any significant improvement over the use of the Flory-Huggins lattice model for representing the bulk free energy terms. Careful analysis of the experimental behavior suggests that configurational effects associated with the flattening of surface adsorbed chains and differences in mer-mer interaction parameters in the bulk and near surface regions are possible origins for the discrepancies between theory and experiment.     

Role of Acid Treatment of the Carbon Support in the Growth of Atomic-Layer-Deposited Pt Nanoparticles for PEMFC Fabrication

Ultrathin films or particles of atomic layer deposition (ALD) on high surface can improve the activity and durability of catalyst fields, so depending on the surface state, the ALD growth mechanism on porous materials should be systematically investigated and optimized to improve their characteristics of catalysts. Herein, a Pt catalyst used in polymer electrode membrane fuel cell (PEMFC) applications is synthesized through fluidized-bed-reactor ALD on carbon black whose surface is modified through treatment with citric acid. The functional groups, analyzed through X-ray photoelectron spectroscopy (XPS), are found to be maximized after 60 min of acid treatment with stirring. Compared with bare carbon (untreated), the acid-treated carbon presents rich oxidized functional groups and abundant defects but lower surface areas and pore volumes. After ALD Pt deposition, highly dense, uniform, and well-dispersed Pt nanoparticles (NPs) are observed on the carbon black subjected to acid treatment, because of the favorable surface modifications for ALD growth resulting from the acid treatment. The ALD-Pt NPs on the acid-treated carbon exhibit larger electrochemical active surface areas, improved oxygen reduction reactions, and PEMFC performances, when compared with that of NPs on bare carbon with similar Pt weight loading.     

The role of hydrophobic interaction in phase transition and structure formation of lipid membranes and proteins

The hydrophobic interaction arises from the ordered structure of water around nonpolar groups of molecules in an aqueous solvent. Because biological systems are made of various macromolecules and amphiphiles which are suspended in aqueous solution, the hydrophobic interaction plays a very important role in the formation of higher-order structure and phase transitions in biological systems. Considering the hydrophobic interaction, the van der Waals interaction and the entropic effect, an equation of state of a lipid membrane was obtained which was analogous to the van der Waals equation. The characteristics of the lipid bilayer phase transition as well as the phase behaviors of a lipid monolayer were explained by this equation of state. Experimental evidence was obtained from ultrasonic measurements which indicated that its phase transition accompanys significant critical phenomena. Analysis of the hydrophobicity of amino acid sequences revealed that the morphology of the proteins was determined by the hydrophobicity alone. The essential role of the hydrophobic interaction in the morphogenesis of proteins could be confirmed by a denaturation experiment on a soluble protein, carbonic anhydrase B. Fluorescence measurements showed that an intermediate state, the so-called molten globule state, had a quite hydrophobic core, indicating that the globule shape of this protein is stabilized by the hydrophobic interaction.     

Linear and Nonlinear Optical Characterization of PolyDCHD-HS Films

Waveguiding films of the highly soluble polycarbazolydiacetylene polyDCHD-HS were prepared by spin coating and characterized at different wavelengths: 5 dB/cm propagation losses were observed at 1321 nm.Measurements of the third order nonliearity at 1064nm with the surface plasmon resonance method gave the valueχ(3)= i4.4×10-17+3.5×10-18 m2/V2.     

Linear and Nonlinear Optical Characterization of PolyDCHD-HS Films

Waveguiding films of the highly soluble polycarbazolydiacetylene polyDCHD-HS were prepared by spin coating and characterized at different wavelengths: 5 dB/cm propagation losses were observed at 1321 nm.Measurements of the third order nonliearity at 1064nm with the surface plasmon resonance method gave the valueχ(3)= i4.4×10-17+3.5×10-18 m2/V2.     

Effect of Interfaces on the Crystallization Behavior of PDMS

The reversible thermal behavior of a non-entangled semicrystalline polymer, poly(dimethylsiloxane), PDMS, was investigated in the presence of sub-micron particles. Filled polymer systems of this type are characterized by a large surface-to-volume ratio but lack the external confinement that is typical for a thin film geometry. Differential-scanning calorimetry (DSC) measurements indicate that the presence of the nanometric solid additives enhances the crystallization rate as compared to native PDMS melts. Different types of additives and surface interactions resulted in a similar effect, suggesting that the origin of the enhanced crystallinity is non-specific. The effect is attributed to entropic interactions in the boundary layer.     

聚合物微腔的研制及其特性分析

采用ＢＭＰＰＶ：ＰＶＫ的混合物作国源介质，将其按一定比例溶于氯仿中，并旋涂在具有９９．５％的反射率的ＤＢＲ上，其上蒸发３００ｎｍ的银膜，形成了面发射型微腔结构，其中ＤＢＲ在入射腔面，银膜为反射腔面，在激发波长３３７．１ｎｍ，频率２０Ｈｚ脉宽１０ｎｓ的氮分子激光器泵浦下，光谱明显等窄化，出现４６０ｎｍ和５３０ｎｍ两个比较强的发光峰，主峰国４６０ｎｍ半宽度为７ｎｍ。     

A Change of Phase Morphology in Poly Lactic Acid/Poly Methyl Methacrylate Blends Induced by Graphene Nano Sheets

Blending of polymeric materials is an effective way to obtain materials with specific properties, since the properties of these multiphase polymeric materials are not only affected by the properties of the component polymers but also by the morphology formed. The research described here was focused on investigation of the morphology of polymer blends of poly lactic acid (PLA) and poly methyl methacrylate (PMMA) and the PLA/PMMA blends containing various amounts of graphene nano plates, (GNP). In this work, the blends were prepared by solution casting and the morphologies of these nano filled polymer blends were studied. By adding graphene nano plates into the PLA/PMMA blends, the morphology changed for all compositions. It was very interesting to note that the GNP were found to be preferentially located in one of the polymer phases, different for the different loadings, and its location determined the final morphology of the PLA/PMMA blends. The morphology of the blends was observed by SEM and the composition-morphology dependence responses were investigated using a Fourier transform infra-red (FTIR) spectroscopy technique.     

高分子锚定的流体膜

将高分子自洽平均场理论和膜弹性理论结合起来研究高分子锚定流体膜体系，得到了高分子链热力学平衡浓度的分布和膜的形状.由于膜对高分子的不可穿透性，造成高分子可以实现的构象受到限制，导致高分子对膜施加不均匀的熵压，从而锚定点附近的膜弯离高分子，这些结果符合前人的理论分析和蒙特卡罗模拟的结果.此外，考察了膜和高分子链段之间的相互作用，高分子链长以及膜的弯曲刚性、张力对膜形变的影响. 关键词： 高分子 流体膜 自洽场理论 Helfrich膜弹性理论     

Dissociation of the light-harvesting membrane protein complex I from Rhodobacter sphaeroides under high hydrostatic pressure

The light-harvesting complex 1 (LH1) from Rhodobacter sphaeroides is an excellent model system for investigating the stability of oligomeric membrane proteins under high hydrostatic pressure. The currently investigated LH1 forms a 16-meric ring structure of B825 subunits. B825 is a heterodimer of transmembrane α- and β-polypeptide chains, which non-covalently binds two bacteriochlorophyll a molecules. These pigment molecules were used as intrinsic spectroscopic sensors to follow the dissociation reaction. Our results demonstrate that the LH1 dissociates into B825 subunits through an intermediary tetrameric unit B845. The dissociation mechanism depends on pressure. At ～200–500?MPa the dissociation corresponds to a pseudo-first-order reaction, characterised by the apparent reaction rate at atmospheric pressure k₀?=?3·10^?5?s^?1, activation volume ΔV^??=??4?mL/mol, and free energy of activation ΔG^??=?26?kJ/mol. Below 200?MPa and above 500?MPa, the reaction is more complex, including further dissociation of B825 into monomers B777.     

Effect of Structure of Graft on the Properties of Graft Copolymers of Acrylamide and Surfactant Macromonomers Dilute Aqueous Solutions

Several surfactant macromonomers (SMM_xyz) were prepared by using triblock polymers of ethylene oxide (EO) and propylene oxide (PO) (PO_x–EO_y–PO_z triblock polymer, x: y: z represent the weight ratio of the different blocks). Then graft copolymers of acrylamide and SMM_xyz (PAM-g-SMM_xyz) were synthesized. The effects of EO/PO mole ratio, length of grafted SMM_xyz and the three relative block sizes on the surface activity and thermo-associativity of PAM-g-SMM_xyz dilute solutions were studied. The results showed that the surface tension decreased with increasing PO in the graft at 30°C and decreased with the length of the graft when the temperature was higher than the cloud points of the grafted PO_x–EO_y–PO_z chains, regardless of EO/PO ratio. When the EO/PO ratio was the same in the SMM_xyz, the PAM-g-SMM_xyz with higher PO content at the graft end had higher surface activity. With increasing temperature, the hydrodynamic radius (R_h) of PAM-g-SMM_xyz in dilute aqueous solution increased. The polymer with shorter grafts may have much more intermolecular interaction points and there were more polymer chains in the polymeric aggregates, which led to R_h increasing with decreasing length of graft. In addition, when the EO/PO was not more than 1:1.74, the three relative block sizes had no great influence on the temperature-associativity of PAM-g-SMM_xyz. However, for PAM-g-SMM₂₁₇ and PAM-g-SMM₇₁₂, the R_h of PAM-g-SMM₂₁₇ was smaller than PAM-g- SMM_712.     

分散有ZnS:Mn2+纳米超微粒的有机薄膜的制备和光学性质

近年来,半导体超微粒的合成及光物理性质研究已成为活跃的领域.由于量子尺寸效应引起的量子点能级结构的变化及其光学性质已经作了大量研究[1-4].1993年,Bhar-gava首次报导了化学反应合成的ZnS Mn超微粒的光学性质[5],掺杂半导体纳米材料的出现,为纳米科学的研究开辟了新的领域.     

Surface Distribution of Topological Defects on Axisymmetric

We propose a general method of deterrnining the distribution of topological defects on axisymmetric surface, and study the distribution of topological defects on biconcave-discoid surface, which is the geometric configuration of red blood cell. There are three most possible cases of the distribution of the topological defects on the biconcave surface： four defects charged with 1/2, two defects charged with ＋1, or one defect charged with 2. For the four defect charged with 1/2, they sit at the vertices of a square imbedded in the equator of biconcave surface.     

Distribution of Topological Defects on Axisymmetric Surface

We propose a general method of determining the distribution of topological defects on axisymmetric surface,and study the distribution of topological defects on biconcave-discoid surface, which is the geometric configuration of red blood cell. There are three most possible cases of the distribution of the topological defects on the biconcave surface:four defects charged with 1/2, two defects charged with 1, or one defect charged with 2. For the four defect charged with 1/2, they sit at the vertices of a square imbedded in the equator of biconcave surface.     

多溶剂响应自折叠水凝胶

本文基于寡聚乙二醇甲醚甲基丙烯酸酯(OEGMA)和2-甲基-2-丙烯酸-2-(2-甲氧基乙氧基)乙酯(MEO₂MA)设计了一种自折叠水凝胶. 在室温下,P(MEO₂MA-co-OEGMA)凝胶能够在多种溶剂中自折叠形成三维结构. 凝胶不均匀膨胀导致内应力增强,从而使得片状凝胶可以在三维结构和二维形状之间进行可逆转换. 研究表明,凝胶组成、固化气体环境和成型过程对水凝胶的自折叠过程起着重要的影响.     

Multiscale molecular dynamics simulations of membrane remodeling by Bin/Amphiphysin/Rvs family proteins

Membrane curvature is no longer thought of as a passive property of the membrane; rather, it is considered as an active, regulated state that serves various purposes in the cell such as between cells and organelle definition. While transport is usually mediated by tiny membrane bubbles known as vesicles or membrane tubules, such communication requires complex interplay between the lipid bilayers and cytosolic proteins such as members of the Bin/Amphiphysin/Rvs(BAR) superfamily of proteins. With rapid developments in novel experimental techniques, membrane remodeling has become a rapidly emerging new field in recent years. Molecular dynamics(MD) simulations are important tools for obtaining atomistic information regarding the structural and dynamic aspects of biological systems and for understanding the physics-related aspects. The availability of more sophisticated experimental data poses challenges to the theoretical community for developing novel theoretical and computational techniques that can be used to better interpret the experimental results to obtain further functional insights. In this review, we summarize the general mechanisms underlying membrane remodeling controlled or mediated by proteins. While studies combining experiments and molecular dynamics simulations recall existing mechanistic models, concurrently, they extend the role of different BAR domain proteins during membrane remodeling processes. We review these recent findings, focusing on how multiscale molecular dynamics simulations aid in understanding the physical basis of BAR domain proteins, as a representative of membrane-remodeling proteins.     

Tip-Enhanced Raman Spectroscopy and Mapping of Graphene Sheets

Abstract: Single graphene sheets, a few graphene layers, and bulk graphite, obtained via both micromechanical cleavage of highly oriented pyrolytic graphite and carbon vapor deposition methods, were deposited on a thin glass substrate without the use of any chemical treatment. Micro-Raman spectroscopy, tip-enhanced Raman spectroscopy (TERS), and tip-enhanced Raman spectroscopy mapping (TERM) were used for characterization of the graphene layers. In particular, TERM allows for the investigation of individual graphene sheets with high Raman signal enhancement factors and allows for imaging of local defects with nanometer resolution. Enhancement up to 560% of the graphene Raman band intensity was obtained using TERS. TERM (with resolution better than 100 nm) showed an increase in the number of structural defects (D band) on the edges of both graphene and graphite regions.     

热处理对CH薄膜表面粗糙度及力学性能的影响

利用低压等离子体化学气相沉积法制备厚度约为7 m的辉光放电聚合物薄膜,将制备的薄膜样品放入通有氩气保护的热处理炉中加热至300 ℃,分别进行6,10,24 h的保温热处理。通过白光干涉仪观察分析了不同保温时间下辉光放电聚合物薄膜的表面粗糙度; 利用傅里叶变换红外吸收光谱分析了300 ℃条件下不同保温时间对薄膜结构的影响; 采用纳米压痕仪表征了不同保温时间热处理后,薄膜硬度及模量的变化。结果表明:随着保温时间的增加,薄膜的表面均方根粗糙度由12 nm降至4.43 nm。薄膜结构中甲基的相对含量减少,双键的相对含量增加,碳链变长,同时薄膜网络结构的交联化程度增强。硬度和模量随着保温时间的增加先减小后增大。     

Membrane Organization and Dynamics of the G-Protein-Coupled Serotonin<Subscript>1A</Subscript> Receptor Monitored Using Fluorescence-Based Approaches

The G-protein-coupled receptor (GPCR) superfamily represents one of the largest classes of molecules involved in signal transduction across the plasma membrane. Fluorescence-based approaches have provided valuable insights into GPCR functions such as receptor–receptor and receptor–ligand interactions, real-time assessment of signal transduction, receptor dynamics on the plasma membrane, and intracellular trafficking of receptors. This has largely been possible with the use of fluorescent probes such as the green fluorescent protein (GFP) from the jellyfish Aequoria victoria and its variants. We discuss the potential of fluorescence-based approaches in providing novel information on the membrane organization and dynamics of the G-protein-coupled serotonin_1A receptor tagged to the enhanced yellow fluorescent protein (EYFP). These authors contributed equally to the work.     

低温等离子体表面处理技术在生物医用材料中的应用

合成高分子材料无法完全满足作为生物医用材料所需要的生物相容性和高度的生物功能要求，为解决上述问题，文章介绍了一种表面处理方法－等离子体表面改性技术以其特有的优点在生物医用材料中的应用情况，通过等离子体处理后，能够在高分子材料表面固定生物活性分子，达到为生物医用材料的目的。