混合高聚物分相过程标度、分形与Monte Carlo模拟

基于光散射、Monte Carlo模拟标度理论和分形(Fractal)概念研究和分析了高分子混合体系不稳相分离过程结构函数的标度行为和成因, 结果表明相分离的形态是一种分形结构, 其分形维数不随时间变化. 结构函数的标度行为起源于相态的分形结构. 相态的分形结构是不稳相分离特征之一.     

Recent advances in starch–clay nanocomposites

Biological nanocomposites are a valuable addition to the existing nanocomposite materials and eventually can substitute petroleum-based composite materials in numerous applications due to their inherent advantages such as biodegradability, eco-friendliness, low cost, and easy availability to name a few. Recently, polymer–clay nanocomposites have achieved much more attention due to their enhanced properties such as size dispersion and significant enhancement in physicochemical and mechanical properties in comparison to the pure polymer systems. Among various biopolymers, starch is one of the most abundant natural polymers on the earth and is highly valuable due to its chemical and physical properties. Starch polymer has highly increased potential as an alternative to petroleum-based materials. However, starch cannot be used alone and starch–clay nanocomposite has emerged as a new potential green sustainable material. This article focuses on recent progress in starch-based nanocomposites with particular emphasis on starch–clay nanocomposite preparation, properties, and applications.     

Thermoplastic starch blends: A review of recent works

The aim of this review is to discuss the recent developments in thermoplastic starch blends. Starch has been considered as an excellent candidate to partially substitute synthetic polymer in packaging, agricultural mulch and other low-cost applications. Recently, the starch granules were plasticized using different plasticizers under heating and shearing, giving rise to a continues phase in the form of a viscous melt which can be processed using traditional plastic processing techniques, such as injection molding and extrusion. This kind of starch composites is called thermoplastic starch. Unfortunately, thermoplastic starch presents some drawbacks, such as low degradation temperatures, which make it difficult to process, poor mechanical properties and high water susceptibility. Much work has been carried out to overcome these drawbacks, including the combination of thermoplastic starch with other polymers, aiming at lowering the cost and enhancing the biodegradability of the final product.     

Effects of natural polymer acetylation on the anaerobic bioconversion to methane and carbon dioxide

The successful production of novel biodegradable plastic copolymers incorporating both synthetic plastic formulations, such as polystyrene, and naturally occurring biodegradable polymer components, such as cellulose, starch, or xylan, requires stable chemical bonding between these polymers. Modification of the natural polymers through acetylation of the available hydroxyl groups permits the formation of appropriate film-forming plastic copolymers. However, modification of natural polymers has been demonstrated to result in decreased attack by microbial catalysts. For this study, the abundant natural polymers cellulose, starch, and xylan were substituted with acetate to various degrees, and the effect of this modification on the anaerobic biodegradation was assessed using the biochemical methane potential (BMP) protocol. Significant reduction in anaerobic biodegradability resulted with all polymers at substitution levels of between 1.2-1.7. For the xylan acetate series, the trends for anaerobic biodegradation were in good agreement with reduced enzymatic hydyolysis using commercially available xylanase preparations.     

Free energy of mixing of cross-linked polymer blends

Free energy of mixing of cross-linked polymer blends is derived, as a modification to the Flory-Huggins-de Gennes free energy functional for linear polymer blends. The latter arrives from the assumption of mean-field, short-range thermal interactions among ideal Gaussian chains. However, upon cross-linking a linear chain, the chain no longer remains Gaussian; new chain architectures belying the threadlike image of linear chains emerge. Fractal dimensions of these nonlinear chain clusters convene and command new entropic interactions. Topological constraints by cross-links introduce long-range nonequilibrium elastic forces. Relatively shorter range steric repulsions between fractal network surfaces may arrive if cross-linking is carried out inside the blend's thermodynamically unstable region. Modified free energy has been used to highlight experiments on phase instability of cross-linked polymer blends.     

磨盘碾磨聚丙烯粒度分布与接枝率的研究

用分形几何方法研究了磨盘碾磨中聚丙烯 (PP)的粉碎和固相力化学接枝 .用粒度分析仪测定经磨盘碾磨聚丙烯的粒度分布 ,用分形理论处理实验数据 .结果表明 ,PP粒度分布存在无标度区 ,具有线性分形特征 ,磨盘碾磨对PP粒子分形行为有较大影响 ,聚丙烯粒度分布的分维值随碾磨次数的增加而增大 .磨盘碾磨中聚丙烯固相力化学接枝的实验结果表明 ,N 羟甲基丙烯酰胺在聚丙烯表面上的接枝率亦随碾磨次数增加而增加 ,即与聚丙烯粒度分布的分维值相关 .因此 ,可用分数维定量描述聚丙烯粒子在磨盘碾磨中的粉碎规律 ,揭示了N 羟甲基丙烯酰胺在聚丙烯表面固相力化学接枝反应的本质 .     

Application of fractal geometry for studies of heterogeneity properties of nanomaterials

Calculations based on the fractal geometry in the estimation of surface heterogeneity are superior compared with conventional calculation methods (e.g. from the data of gas adsorption or X-ray radiation scattering) as they can be applied without limitation as far as the range of surface sizes of the studied structures is concerned. This paper presents structural characteristics of carbon and carbon- free nanomaterials based on the determined surface and volumetric fractal coefficients. Fractal coefficients were determined from the data obtained by means of two independent methods: sorptometry and atomic force microscopy (AFM). Correlation between porosity parameters and fractal coefficients is presented.     

Fractal Growth of Giant Amphiphiles in Langmuir-Blodgett Films

Chinese Journal of Polymer Science - Fractal structures have attracted considerable scientific interest, and fractal geometry is an effective tool to study the complicated structure and dynamic...     

淀粉基高分子材料的研究进展

概述了近5年国内外在淀粉的化学、物理改性及其作为一种材料使用方面取得的最新研究进展.淀粉的化学改性主要介绍了淀粉的酯化、醚化、氧化、交联、接枝共聚等,而物理改性主要介绍了淀粉分别与黏土、脂肪族聚酯、聚乙烯醇以及纤维素等天然大分子的共混改性,同时还介绍了通过酸化制备淀粉纳米晶.淀粉基材料除了用于制备可生物降解塑料、吸附材...     

Surface Roughness Characterization of Poly(methylmethacrylate) Films with Immobilized Eu(III) β-Diketonates by Fractal Analysis

The structural complexity of the 3-D surface of poly(methylmethacrylate) films with immobilized europium β-diketonates was studied by atomic force microscopy and fractal analysis. Fractal analysis of surface roughness revealed that the 3-D surface has fractal geometry at the nanometer scale. Poly(methylmethacrylate) (PMMA) as immobilization matrix is dense and uniform, and a tendency for formation of chain structures was observed. Fractal analysis can quantify key elements of 3-D surface roughness such as the fractal dimensions D _f determined by the morphological envelopes method of the Eu(DBM)₃ and Eu(DBM)₃ · dpp nanostructures, which are not taken into account by traditional surface statistical parameters.     

分形理论及其在高分子科学中的应用

介绍了分形的基本概念，分形维数的定义及计算方法，讨论了近年来分形理论在高分子科学研究方面的一些应用，内容主要包括高分子溶液、高分子材料的磨损，断裂及界面，高分子结晶过程、导电高分子等。     

生物降解高分子/羟基磷灰石复合材料研究进展

由于高分子/HA复合材料兼具HA优良的生物性能和高分子材料良好的力学性能而受到了广泛的重视.本文综述了近年来生物降解高分子/羟基磷灰石复合材料的研究进展,介绍了胶原及其衍生物、聚酯、甲壳素及其衍生物、淀粉等可降解高分子材料与羟基磷灰石复合作为骨修复材料的研究进展,并对此类材料存在的问题和发展前景进行了讨论.     

Anionic graft polymerization of methacrylonitrile on potassium starch alkoxide

The anionic graft polymerization of methacrylonitrile on potassium starch alkoxide in dimethyl sulfoxide was studied. Factors affecting the graft polymerization such as monomer and alkoxide concentrations as well as temperature were investigated. The yield of the graft polymers was found to increase with alkoxide concentration, and it was possible to incorporate all the starch into graft polymer. On increasing the monomer concentration the graft polymer yield increased to a flat maximum. At the higher monomer concentrations, the efficiency of monomer in giving graft polymer decreased due to increased homopolymer formation. The composition of the graft polymers varied with increasing monomer concentration, graft polymers having about 40–65% of grafted starch were obtained. With increasing temperature (10 to 60°C), the yield of graft polymer decreased, there was more homopolymerization, but the amount of starch incorporated in the graft remained constant. The structure of the graft polymers was deduced from hydrolysis of the starch backbone of the graft polymers by dilute mineral acid and the determination of the molecular weights of the grafted side chains, and from oxidation by periodic acid, which showed the extent of grafting at the secondary hydroxyl groups. These results have shown that by anionic graft polymerization it is possible to obtain graft polymers having more densely packed grafted side chains of relatively low molecular weights than those obtained previously by free-radical graft polymerization.     

Preparation and Structure of Microporous Silica Membranes

Silica sols have been prepared in an alcoholic solution by hydrolysis and condensation of TEOS (tetra-ethyl-ortho-silicate) molecules as a function of water and nitric acid concentration. The polymers are intended as precursors for ceramic, gas separation membranes. These molecules show fractal behavior as determined by SAXS (Small Angle X-ray Scattering). Microporosity of dried and calcined silica polymers is determined by N₂-adsorption at 77 K. Fractal dimension and porosity increase with increasing acid concentration. Both the sol structure and the drying kinetics determine the porosity values. N₂-adsorption isotherms are not very suitable for the determination of pore size distributions of microporous silica.     

高磺化度聚苯胺体系中的分形结构研究

通过透射电镜的观察研究发现磺化聚苯胺的胶体聚集体和胶粒内部结构都具有分形体的特征 ,从而将分形的概念及其数学模型引入共轭导电聚合物体系之中 .磺化聚苯胺胶体的聚集体为很不均匀的分支状开放结构 ,其形成过程可用扩散控制集团聚集模型 (DLCA)进行模拟 ,计算机模拟生成的图形及其分形维数都与实验观测结果相当吻合 .胶粒由于是在分散介质所形成的平均化场中生成 ,屏蔽效应减弱 ,是比由它组成的聚集体要致密的球形结构 ,该结构的生成可用随机雨点模型模拟且结果相近 .     

Branched Crystalline Patterns Formed Around Poly(ethylene oxide) Dots in Humidity

Branched patterns reminiscent of diffusion‐limited aggregation form around poly(ethylene oxide) dots on Au surfaces in humidity by crystallization of polymer chains in water‐assisted diffusion, involving fractal‐like structure and dense branching‐like morphology (DBM). Higher humidity leads to a slower growth of crystal lamellae. Crystal growth promotes outward diffusion. Fractal‐like lamellae are viewed flat‐on. Due to the reduction of chain availability in the diffusion field, the fractal‐like structure turns into DBM.     

Structure and mechanical properties of polysaccharides

This article serves both as a review of polysaccharides as gelling and thickening agents and as an introduction to polysaccharides, other than starch and cellulose, their source and extraction, and how molecular detail is reflected in their macromolecular and supramolecular properties. The whole is summarised for workers in the synthetic polymer area interested in new “green” polymers. We also introduce results for a new polysaccharide extracted from a Nigerian tree pod, and describe details of its structural and physicochemical characterisation including light scattering and rheological measurements.     

Evaluation of surface roughness of hydrogels by fractal texture analysis during swelling

The surface of a biomaterial reacts in contact with biological fluids. Hydrogels are used to prepare biomaterials. The surface roughness of materials can be explored by several techniques. However, when considering hydrogels, the surface examined in the dry state does not reflect the final conformation. How the surface roughness is affected by swelling has been little explored by quantitative methods. We have evaluated the surface roughness of poly(2-hydroxyethyl methacrylate) (i.e., pHEMA) by image analysis. Images of disks, prepared from linear pHEMA, were obtained on a light microscope after various incubation times in saline. Fractal texture analysis was done on images to determine the fractal dimension D. In this study, D exhibited a significant decrease during swelling and was highly correlated with the swelling ratio (r2 = 0.994, p < 0.00001). Water uptake by the surface of the polymer affected the surface roughness. Image analysis using fractal algorithms appears to be the most interesting technique for the quantitative exploration of surfaces of hydrated materials that cannot be measured by conventional methods.     

Thermal degradation of aliphatic polyamides studied by field ionization and field desorption mass spectrometry

The aliphatic polyamides nylon 6.6, 6.9, 6.10, 6.12, 12.6, 12.10, and 12.12 of the diamine dicarboxylic acid-type were pyrolyzed in the ion source of a double-focusing mass spectrometer and the thermal degradation products were recorded by field ionization (FI) and field desorption (FD) mass spectrometry (MS). In the FI mode, several series of thermal degradation products differing in the number of polymer repeating units were detected up to 1000 Daltons. The main products were oligomers and, in addition, protonated dinitriles and various protonated nitriles are formed in large amounts except for nylon 6.6 and nylon 12.6. These two polymers form, in contrast to all other samples, large amounts of protonated amides and diamines. The technique employed allows distinction between oligomers already present in the original polymer and oligomers formed by thermal fission of bonds in the polymer chain. Reaction mechanisms are given that explain the products observed. High resolution experiments and accurate mass measurements were performed to confirm the proposed structures. In the FD mode, cationized oligomers (attached mostly to a sodium cation) were observed below 200°C with the dimers being the base peak for most samples. In contrast to the FI results, the monomers were only detected at very low intensities. Similarly, only weak signals for additional thermal degradation products were registered except for nylon 12.6. At higher temperatures the FD mass spectra gave protonated and doubly protonated oligomers in the high mass range up to 2000 Daltons, which resulted in complementary structural information about the polymers.     

The effect of inhomogeneous stickiness on polymer aggregation

The aggregation of polymers is important in the formation of marine aggregates and the vertical transport of material in the ocean. A polymer may be inhomogeneous along its length, with associating groups at some points along its length where bonds are more likely to form. In this paper we investigate the effects of inhomogeneous 'stickiness' along the polymer length. We describe the results of three-dimensional off-lattice simulations of polymer-polymer aggregation for four different types of polymer: polymers which are sticky along their entire length, polymers which are sticky at the ends only and two types of polymer which are slightly sticky along their entire length. We examine the mean radius of gyration and the fractal dimension of the resulting aggregates and the dynamics of aggregation. The slightly sticky polymers and the polymers which are sticky only at the ends form aggregates with a higher fractal dimension than the polymers which are sticky along their entire length. However, the mean radius of gyration of the aggregates formed by polymers which are sticky only at the ends is significantly larger than that of the aggregates formed from slightly sticky polymers. The aggregation dynamics are also different for the polymers which are sticky only at the ends compared to the slightly sticky polymers. A single 'stickiness value' is therefore likely to be inadequate to describe a polymer. We also examine the effect of polymer rigidity; it seems that the effect of inhomogeneous stickiness is greater for almost-straight polymers than for coiled chains.