Dewetting and Phase Behaviors for Ultrathin Films of Polymer Blend

Summary: Dynamics of dewetting and phase separation in ultrathin films (thickness is ca. one radius of gyration, ≈1 R_g) of poly(methyl methacrylate) (PMMA) and poly(styrene‐ran‐acrylonitrile) (SAN) blends on Si substrate has been studied by in situ atomic force microscopy (AFM). In the miscible region, a “spinodal‐like” dewetting driven by a composition fluctuation recently predicted by Wensink and Jérôme (Langmuir 2002 , 18, 413) occurs. In the two‐phase region, the dewetting of the whole film is followed by phase separation in the droplets, coupling with the wetting of the substrate by the PMMA extracted by the strong attractive interaction between them.

     

CuSO4 Micro-crystal Lattice Produced by Microcontact Printing

ＩｎｔｒｏｄｕｃｔｉｏｎＴｈｅ ｐｒｅｐａｒａｔｉｏｎｏｆｍｉｃｒｏ ｐａｒｔｉｃｌｅｌａｔｔｉｃｅｗｉｔｈｓｔｒｉｃｔｓｉｚｅｓａｎｄｓｐａｃｅｃｏｎｔｒｏｌｉｓａｎｉｍｐｏｒｔａｎｔｐｒｏｂｌｅｍｔｏｂｅｓｏｌｖｅｄｕｒｇｅｎｔｌｙｉｎｍａｎｙｈｉｇｈ ｔｅｃｈｆｉｅｌｄｓ .Ｔｒａｄｉ ｔｉｏｎａｌｍｉｃｒｏ ｆａｂｒｉｃａｔｉｏｎｍｅｔｈｏｄｉｓｐｈｏｔｏｌｉｔｈｏｇｒａｐｈｙ ,ｂｕｔｉｔｉｓｕｎａｂｌｅｔｏｐｒｏｄｕｃｅａｎｙｐａｔｔｅｒｎｓｏｎａｃｕｒｖｅｄｓｕｒｆａｃｅａｎｄｄｉｆｆｉｃ…     

Effect of Chain‐Length Dependence of Interaction Parameter on Spinodals for Polydisperse Polymer Blends

Summary: The chain‐length dependence of the Flory‐Huggins (FH) interaction parameter is introduced into the FH lattice theory for polydisperse polymer‐blend systems. The spinodals are calculated for the model polymer blends with different chain lengths and distributions. It is found that all the related variables, r_n, r_w, r_z, and chain‐length distribution, have effects on the spinodals for polydisperse polymer blends.

The spinodals at different chain lengths.     

Synthesis and electrochemical properties of graphene-SnS2 nanocomposites for lithium-ion batteries

Graphene-SnS₂ nanocomposites were prepared via a solvothermal method with different loading of SnS₂. The nanostructure and morphology of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The XRD patterns revealed that hexagonal SnS₂ was obtained. SEM and TEM results indicated that SnS₂ particles distributed homogeneously on graphene sheets. The electrochemical properties of the samples as active anode materials for lithium-ion batteries were examined by constant current charge–discharge cycling. The composite with weight ratio between graphene and SnS₂ of 1:4 had the highest rate capability among all the samples and its reversible capacity after 50 cycles was 351 mAh/g, which was much higher than that of the pure SnS₂ (23 mAh/g). With graphene as conductive matrix, homogeneous distribution of SnS₂ nanoparticles can be ensured and volume changes of the nanoparticles during the charge and discharge processes can be accomodated effectively, which results in good electrochemical performance of the composites.     

Effects of chain flexibility on polymer conformation in dilute solution studied by lattice monte carlo simulation

Effects of chain flexibility on the conformation of homopolymers in good solvents have been investigated by Monte Carlo simulation. Bond angle constraint coupled with persistence length of polymer chains has been introduced in the modified eight-site bond fluctuation simulation model. The study about the effects of chain flexibility on polymer sizes reveals that the orientation of polymer chains under confinement is driven by the loss of conformation entropy.The conformation of polymer chains undergoing a gradual change from spherical iso-diametric ellipsoid to rodlike iso-diametric ellipsoid with the decrease of polymer chain flexibility in a wide region has been clearly illustrated from several aspects. Furthermore, a comparison of the freely jointed chain (FJC) model and the wormlike chain (WLC) model has also been made to describe the polymer sizes in terms of chain flexibility and quasi-quantitative boundary toward the suitability of the models.     

静压轴径轴承静态特性的数值模拟分析

气体润滑轴承具有摩擦小、寿命长、精度高等优点,已经在精密工程等许多领域有着十分广阔的应用。文中对气体润滑基本方程Reynolds方程进行了分析,利用FLUENT对透平膨胀机用静压轴径轴承模型进行了数值模拟,得到轴承表面的压力分布;并逐一研究了供气压力、偏心率和轴承结构参数等因素对静压气体轴承静态特性的影响规律。     

Crystallization and morphology of poly(ethylene oxide‐b‐lactide) crystalline–crystalline diblock copolymers

The crystallization behaviors and morphology of asymmetric crystalline–crystalline diblock copolymers poly(ethylene oxide‐lactide) (PEO‐b‐PLLA) were investigated using differential scanning calorimetry (DSC), wide angle X‐ray diffraction (WAXD), and microscopic techniques (polarized optical microscopy (POM) and atomic force microscopy (AFM)). Both blocks of PEO₅‐b‐PLLA₁₆ can be crystallized, which was confirmed by WAXD, while PEO block in PEO₅‐b‐PLLA₃₀ is difficult to crystallize because of the confinement induced by the high glass transition temperature and crystallization of PLLA block with the microphase separation of the block copolymer. Comparing with the crystallization and morphology of PLLA homopolymer and differences between the two copolymers, we studied the influence of PEO block and microphase separation on the crystallization and morphology of PLLA block. The boundary temperature (T_b) was observed, which distinguishes the crystallization into high‐ and low‐temperature ranges, the growth rate and morphology were quite different between the ranges. Crystalline morphologies including banded spherulite, dendritic crystal, and dense branching in PEO₅‐b‐PLLA₁₆ copolymer were formed. The typical morphology of dendritic crystals including two different sectors were observed in PEO₅‐b‐PLLA₃₀ copolymer, which can be explained by secondary nucleation, chain growth direction, and phase separation between the two blocks during the crystallization process. Lozenge‐shaped crystals of PLLA with screw dislocation were also observed employing AFM, but the crystalline morphology of PEO block was not observed using microscopy techniques because of its small size. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1400–1411, 2008     

Detection of complement C1-inhibitor with a piezoelectric immunosensor

A novel piezoelectric immunosensor has been developed for the detection of human complement C1-inhibitor. Anti-C1-inhibitor antibody was immobilized onto the gold electrodes of a 9 MHz AT-cut piezoelectric crystal. Coating the crystal with polyethyleneimine adhesion, followed by a glutaraldehyde cross-linking method to immobilize antibody showed better results than the physical adsorption method with respect to sensitivity and reproducibility. Under the optimized experimental conditions, the sensor showed good response to the C1-inhibitor in the range from 2.0 × 10^–8 to 1.2 × 10^–6 g. Other proteins in human serum did not remarkably interfere with the detection. The crystals could be regenerated 5 times, when bound materials on the crystal surface were eluted by strong acid and strong alkali solution and subsequently cleaned in an ultrasonic cleaner.     

Crystalline morphology evolution in PCL thin films

The transition of crystalline morphology is revealed in poly(?‐caprolactone) (PCL) thin films as the polymer film thickness changes from hundreds of nanometers to several nanometers. The PCL can crystallize into spherulites, dense‐branching morphology (DBM), or dendrites, depending on the polymer film thickness. It was found that when the polymer film thickness approaches 2Rg (radius of gyration of polymer), there is a remarkable change in crystalline morphology. Under this condition, the polymer crystallization is a diffusion‐controlled process. When the value of polymer film thickness closes to Rg, PCL cannot crystallize, and a dewetting phenomenon will take place. Moreover, polymer morphology can be controlled by varying supercooling. The effect of molecular weight on polymer morphology has been investigated. The main factors that affected pattern formation in nonequilibrium crystallization are also discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1303–1309, 2005