Sterically stabilized emulsion polymerization of styrene: Pseudo‐semicontinuous approach

The sterically stabilized emulsion polymerization of styrene initiated by a water‐soluble initiator at different temperatures has been investigated. The rate of polymerization (R_p) versus conversion curve shows the two non‐stationary‐rate intervals typical for the polymerization proceeding under non‐stationary‐state conditions. The shape of the R_p versus conversion curve results from two opposite effects—the increased number of particles and the decreased monomer concentration at reaction loci as the polymerization advances. At elevated temperatures the monomer emulsion equilibrates to a two‐phase or three‐phase system. The upper phase is transparent (monomer), and the lower one is blue colored, typical for microemulsion. After stirring such a multiphase system and initiation of polymerization, the initial coarse polymer emulsion was formed. The average size of monomer/polymer particles strongly decreased up to about 40% conversion and then leveled off. The initial large particles are assumed to be highly monomer‐swollen particles formed by the heteroagglomeration of unstable polymer particles and monomer droplets. The size of the “highly monomer” swollen particles continuously decreases with conversion, and they merge with the growing particles at about 40–50% conversion. The monomer droplets and/or large highly monomer‐swollen polymer particles also serve as a reservoir of monomer and emulsifier. The continuous release of nonionic (hydrophobic) emulsifier from the monomer phase increases the colloidal stability of primary particles and the number of polymer particles, that is, the particle nucleation is shifted to the higher conversion region. Variations of the square and cube of the mean droplet radius with aging time indicate that neither the coalescence nor the Ostwald ripening is the main driving force for the droplet instability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 804–820, 2003     

纵波模拟演示装置

介绍了一种纵波模拟演示装置，并给出了其结构要点及演示效果，实现了对纵波行波的演示。     

Reversible 5′-end biotinylation and affinity purification of synthetic RNA

A reversible biotinylation phosphoramidite was synthesized and incorporated onto the 5′-end of an oligoribonucleotide on a solid phase synthesizer. After cleavage and deprotection, the crude synthetic oligomer mixture was incubated with NeutrAvidin^® coated microspheres, and the failure sequences removed by washing with a buffer followed by treating the microspheres with tetrabutylammonium fluoride to give a high quality unmodified full-length oligoribonucleotide.     

Characteristics in optimization of CGH for array generator

A method of simulated annealing in optimization of a computer generated holo-gram(CGH)is presented.The characteristics of energy in annealing curve are analyzed.Thecooling schedule such as giving an initial temperature,the temperature function,the numberof interactions and stopping criterion are discussed.As an example,an optimization of phaserelief kinoform,a CGH with multiple phase levels,is implemented.     

利用相位共轭技术补偿光纤中色散效应的条件

利用相位共轭器的频率反转特性的,补偿光纤中的色散效应,在理论上和实验上得到了证明.由色散脉冲的傅里叶交换确定了光纤中二次色散效应可以被忽略的条件,得到了共轭器的反射率和带宽与非线性介质的长度L,参数|K|L之间的关系曲线,找到了影响补偿效果的主要因素.     

F－L模型的状态方程与退禁闭相变图象

用温度场论方法计算了Ｆ－Ｌ模型在有限温度和密度下的状态方程，分析了压强对净重子数密度的等温线．结果表明，在平均场近似下，Ｆ－Ｌ模型所给出的退禁闭相变为一级相变．     

Planar nematic anchoring on SiO-coated substrates

Summary The nematic planar anchoring is usually explained by using simple elastic models: the surface easy axis corresponds to the surface direction that minimizes the excess of nematic elastic energy. When anisotropic rough substrates are used to align nematic liquid crystals, due to the complex surface morphology, usual elastic models are not directly applicable. This paper presents quantitative topographical data of rough substrates, obtained with oblique SiO evaporation under vacuum for nematic planar anchoring. Experimental data are obtained by means of Atomic Force Microscopy and they are used to demonstrate the self-affine nature of these substrates and to relate the nematic anchoring with the anisotropy of the local fractal properties of the substrate itself. Paper presented at the I International Conference on Scaling Concepts and Complex Fluids, Copanello, Italy, July 4–8, 1994.     

Microscopic Theory of Blue Phases Ⅰ and Ⅱ of Liquid Crystal

The microscopic theory of the blue phases of chiral liquid crystal is proposed. Beginning with the potential between two molecules, by using the cell model of liquid, applying statistical physical method, the distribution function and the free energy of the system are obtained. By using variational approach and zero-order approximation, the differential equation that the order parameter tensor of the blue phase can satisfy is obtained. Then we change the differential equation to the eigenequation problem in quantum mechanics. Considering the symmetry of the blue phases,the order parameter tensors of blue phases Ⅰ and Ⅱ can be made up of the eigenvectors. Our results are the same as the results of Ginzberg-Landau‘s phenomenological theory. The parameters in the order parameter tensors that we calculate in the located system are close to the predecessors‘ results.     

Radio-Frequency Hexamethyldisiloxane Plasma Deposition: A Comparison of Plasma- and Deposit-Chemistry

This study reports on the effect of input power to hexamethyldisiloxane (HMDSO) plasmas. The power dependence of the plasma-phase species and of the surface chemistry (of the deposits) has been investigated. Neutral and positive molecular species were detected within the plasma using mass spectrometry (MS). Secondary ion mass spectrometry (SIMS) was used to probe the molecular structure of the deposits. The elemental composition of the surface was determined by XPS and the deposition rate was monitored using a vibrating quartz crystal microbalance. Neutral and cationic molecules of mass greater than HMDSO were detected in the plasma. Their formation through ion-molecule reactions is proposed. Changes in the relative concentration of plasma-phase species follow those seen in molecular species detected at the deposit surface. Thus, we believe that the molecular structure of the deposits can be related to the species present in the plasma. While traditionally the dominant mechanism in deposit formation is assumed to be free radical combinations, we propose other possibilities involving cations with the aim of putting forward a new perspective on plasma polymerization mechanisms and thereby stimulating discussion.     

Immiscibility,upper critical solution temperature,and miscibility in blends of poly(vinyl ether)s with polyacrylics: Effects of pendant groups

Various phase behavior of blends of poly(vinyl ether)s with homologous acrylic polymers (polymethacrylates or polyacrylates) were examined using differential scanning calorimetry, optical microscopy (OM), and Fourier‐transformed infrared spectroscopy. Effects of varying the pendant groups of either of constituent polymers on the phase behavior of the blends were analyzed. A series of interestingly different phase behavior in the blends has been revealed in that as the pendant group in the acrylic polymer series gets longer, polymethacrylate/poly(vinyl methyl ether) (PVME) blends exhibit immiscibility, upper critical solution temperature (UCST), and miscibility, respectively. This study found that the true phase behavior of poly(propyl methacrylate)/PVME [and poly(isopropyl methacrylate)/PVME)] blend systems, though immiscible at ambient, actually displayed a rare UCST upon heating to higher temperatures. Similarly, as the methyl pendant group in PVE is lengthened to ethyl (i.e., PVME replaced by PVEE), phase behavior of its blends with series of polymethacrylates or polyacrylates changes correspondingly. Analyses and quantitative comparisons on four series of blends of PVE/acrylic polymer were performed to thoroughly understand the effects of pendant groups in either polyethers (PVE's) or acrylic polymers on the phase behavior of the blends of these two constituents. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1521–1534, 2007