Studies on phase separation rate in porous polyimide membrane formation by immersion precipitation

Phase separation rate during porous membrane formation by immersion precipitation was investigated by light scattering in a polyimide/N‐Methylpyrrolidone (NMP)/water system. In the light scattering measurement, plots of scattered intensity against scattered angle showed maxima in all cases, which indicated that phase separation occurred by a spinodal decomposition (SD). Characteristic properties of the early stage of SD, such as an apparent diffusion coefficient D_app and an interphase periodic distance Λ, were obtained. The growth process of Λ was also followed by light scattering. The growth rate had the same tendency as D_app when water content in the nonsolvent bath and the polymer concentration in the cast solution were changed. The pore size of the final membrane increased with decreasing water content, which was opposite to the tendency of Λ growth rate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 292–296, 2003     

Scaling laws and polystyrene networks: a quasi-elastic light scattering study

Randomly crosslinked networks with a range of crosslink densities were prepared by γ-irradiation. Quasielastic light scattering measurements were made on the gels swollen to equilibrium in cyclohexane at 308, 318 and 333 K. The longitudinal osmotic modulus M_os was obtained from the intensity of the dynamically scattered light, and the cooperative diffusion coefficient D_c calculated from the relaxation rate of the autocorrelation function. The concentration dependence of these parameters at the theta temperature was found to be consistent with the scaling predictions, but at higher temperatures where excluded volume conditions prevail, deviations from scaling behaviour were observed. These discrepancies are probably caused by defects in the network structure.     

The application of small angle scattering techniques to porosity characterization in carbons

Small angle scattering (SAS) techniques offer a number of advantages for the investigation of the nature and behavior of porous materials. In particular, with respect to carbons, the essentially non-intrusive nature of SAS means that along with the more traditional, pre- and post-treatment characterization of carbons, in principle, characterization can also be performed in situ during adsorption and activation processes. In the current communication, the application of the techniques of small angle X-ray (SAXS) and neutron (SANS) scattering is reviewed specifically with respect to porosity characterization in carbons. First, the basis of these techniques is presented. More recent applications of SAXS and SANS to carbon porosity are presented, and their relative attributes are contrasted, including the related technique of contrast matching with SANS to distinguish “closed” from “open” porosity, and its application to elucidation of pore development mechanisms. Applications of other related techniques, such as μSAXS and TGA/SAXS, to carbon characterization and porosity development are also discussed.     

Surface-Enhanced Raman Scattering from Polyimide Model Compounds on Functionalized Metal Surfaces. Part II: Phthalic Anhydride/meta-Aminothiophenol/Silver

The interphase between a polyimide and a metal substrate was modeled by depositing phthalic anhydride (PA) onto a silver substrate pretreated with meta-aminothiophenol (m-ATP) and then curing in a mixture of acetic anhydride and pyridine or triethylamine. Surface-enhanced Raman scattering (SERS) and reflection-absorption infrared spectroscopy (RAIR) were used to determine the molecular structure of the interphase. It was found that m-ATP was adsorbed dissociatively onto silver substrates through the thiol groups. The tilt angle for m-ATP molecules adsorbed on silver substrates was determined using RAIR to be approximately 39°. However, there was no preferred rotational angle of the adsorbed APDS molecules about the molecular axes. When PA was deposited onto m-ATP pretreated silver substrates, anhydride groups of PA reacted with amino groups of m-ATP to form amic acids. When PA/m-ATP/Ag samples were chemically cured in acetic anhydride and pyridine or triethylamine, isoimide was the predominant product regardless of the use of pyridine or triethylamine as catalyst. These results were different from those obtained from PA/APDS/Au systems in which imide was the major product in the presence of triethylamine. These differences in the relative composition of cured products between two model systems were explained by the effect of substituents attached to APDS and m-ATP benzene rings.     

Improved methods for evaluating the molar mass distributions of cellulose in kraft pulp

Multi‐angle laser light scattering (MALLS) was used to characterize birch kraft pulps with respect to their absolute molecular mass distributions (MMDs). The pulps were dissolved in lithium chloride/N,N‐dimethylacetamide and separated by size exclusion chromatography (SEC). The weight‐average and number‐average molecular masses of the cellulose fractions of the pulps obtained from the absolute MALLS measurements were compared with the molar masses obtained by direct‐standard‐calibration relative pullulan standards. Discrepancies between the two detection methods were found, and two ways of correlating the relative pullulan molar masses to the absolute molar masses were examined. In the first method, the correlation was made over a large range of molecular masses. The second method correlated the molecular masses of the standards to the molecular masses of samples by the calculation of fictitious, cellulose‐equivalent molar masses of the standards. With the preferred second method, a more correct MMD of kraft pulp samples could, therefore, be obtained from an SEC system calibrated with narrow standards. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1170–1179, 2003     

Dynamic light scattering studies on random cross-linking of polystyrene in semi-dilute solution

The random cross-linking of appropriately functionalized polystyrene in semi-dilute toluene solution (c = 0.01–0.05 g/mL) was studied by time-dependent measurements of dynamic light scattering. Macroscopic gelation occurred from concentrations as low as 0.02 g/mL. The gelation time, determined from the first appearance of fluctuations of the scattering intensity and the initial amplitude of the intensity correlation function (ICF), decreases markedly from about 100 min to 10 min with an increase of polymer concentration or cross-linker content. After the gel point, the ICFs display a characteristic power-law decay. The power-law exponent, n = 0.75 ± 0.06, does not change with (i) extent of reaction, (ii) polymer concentration, and (iii) cross-linker concentration, within the inspected ranges. This universal behavior is traced back to the fact that gelation took place as a result of random cross-linking of existent macromolecules, whose state of solution does not change markedly during conversion.     

Small-angle neutron scattering from branched epoxide resins

Small-angle neutron scattering experiments in the range of q² from 0.01 to 25 nm⁻² have been carried out on branched epoxide resins based on bisphenol-A at the Institute Laue—Langevin (I.L.L) in Grenoble (q=(4π/λ) sin(θ/2)). Measurements were made with six samples in the range of M_W from 1500 to 19 000 and four concentrations between 1.3 and 10% (w/w) in deuterated diglyme. The results are as follows: (i) The mean square radius of gyration follows a relationship S²_z=4.69×10⁻⁴M^1.20_W (nm²). (ii) In all cases fairly large second virial coefficients A₂ are obtained which, however, decrease strongly with molecular weight. Above M_W=2500, the virial coefficient follows the relationship A₂=1.6M^−0.85_W (mol cm³g⁻²). (ii) The reciprocal particle scattering factor as a function of q² exhibits only a slight upturn and otherwise shows the behaviour of a randomly branched polycondensate. The slight upturn is discussed as being caused by the finite volume of the monomeric unit. Possible reasons for the high exponent in the S²_z versus M_W dependence are briefly discussed.     

基于逐次散射法的海洋-大气矢量辐射传输模式

首先推导了粗糙洋面双向偏振反射模型pBRDF(Bidirectional Polarized Reflectance Distribution Function),并将其与SOSVRT(Successive Order of Scattering Radiative Transfer)矢量辐射传输模式耦合,建立了海洋-大气耦合的矢量辐射传输模式,并对该耦合模式的模拟结果与前人模拟结果进行对比,验证了该耦合模式的可靠性与有效性。不同大气和洋面状态、不同高度的主平面内辐射强度和偏振度的模拟结果表明:pBRDF模型可以很好地模拟不同风速下洋面的偏振反射分布特征;洋面在特定角度具有很高的偏振度,并对大气顶的偏振辐射有很大影响。因此,该耦合模式可以更准确地处理辐射光谱在海洋-大气两种介质间的传输问题,对矢量辐射传输、大气遥感问题的研究有重要意义。     

有限体积法求解立体角离散误差

为解决采用有限体积法求解辐射传输方程时引起离散误差的问题,从有限体积法立体角内热流密度的求解过程出发,运用泰勒级数推导了近似误差的表达式,并分析影响离散误差的各种因素,包括离散射线数,辐射强度分布,假散射及网格比.根据分析结果,采用辐射强度的连续分布模型,模拟了各种因素对误差的影响.结果表明,辐射强度的分布函数对于有限体积法的离散误差有一定程度影响.当增加网格数及减小网格尺寸比时,可以有效地减小离散误差.假散射与离散误差间呈较强的非线性耦合关系.     

各向异性介质涂覆曲面导体目标的散射

由于各向异性介质电磁参数为张量形式,使得各向异性介质涂覆导体目标的电磁散射建模和精确计算相当复杂和困难.引入高阶张量阻抗边界条件,可以大大简化建模过程,提高计算效率.论文针对各向异性介质涂覆曲面导体目标,采用基于平面近似的高阶张量阻抗边界条件,将一维二阶张量阻抗边界条件应用于柱面涂覆目标,二维二阶张量阻抗边界条件应用于三维曲面涂覆目标上,建立二者的高阶张量阻抗边界条件解.设计算例仿真,并与精确解/矩量法解比较.通过仿真,研究了各向异性介质涂覆目标电尺寸、涂覆厚度以及目标形状对高阶张量阻抗边界条件解的精度的影响.