Nanocomposites based on a styrene-acrylate copolymer and organically modified montmorillonite 1. Mechanical properties

The preparation of polymer nanocomposites by mixing a solution of a styrene-acrylate copolymer with a suspension of organically modified montmorillonite in dimethyl formamide is described. Seven different compositions with organomontmorillonite content from 0 to 7 wt.% were prepared and tested. Results of their X-ray diffraction analysis are presented. Data on the influence of organomontmorillonite content on the tensile stress-strain curves, elastic modulus, strength, and ultimate elongation of the nanocomposites are obtained. The concentration dependences of elastic properties of materials with differently oriented platelike nanoparticles is analyzed by using an algorithm elaborated for stepwise calculations of elastic constants with account of the features of structural hierarchy of intercalated and exfoliated nanocomposites. __________ Translated from Mekhanika Kompozitnykh Materialov, Vol. 42, No. 3, pp. 375–388, May–June, 2006.     

The Structure and Properties of Graphite Monofluoride Using the Three-Dimensional Cyclic Cluster Approach

In this paper, we present the theoretical study of the crystal and electron structure of an intercalated compound of graphite —the graphite monofluoride {CF}_n. The latter is widely used as a lubricant under extremely high temperatures and high vacuum, and as a successful cathodic depolarizer in batteries with high energy density. The layered structure of the graphite monofluoride has been confirmed, but statistical distributions of the individual layers are possible. This fact helps in understanding the problems linked to an experimental determination of the structure of this material. Small interlayer dissociation energies show that the bonding between the individual layers is mainly due to the weak interlayer electrostatic forces, which explains the excellent lubricant properties of this material. Band structure calculations reveal that, whereas some layer arrangements of the bulk material lead to insulating properties, others have a conductive character. This fact explains the weak overall conductive properties of synthetic graphite monofluoride.     

层间阴离子对四元水滑石超分子作用力的影响

构建一价阴离子(X=F^?, Cl^?, Br^?, I^?, NO₃^?, OH^?)插层铜锌镁铝四元水滑石(CuZnMgAl-X)周期性计算模型, 采用密度泛函理论(DFT), 选取CASTEP程序模块, 对体系进行几何全优化, 从结合能、结构参数、Mulliken布居、氢键布居、态密度等角度研究了不同层间阴离子的分布形态以及其对主客体间超分子作用的影响. 结果表明, 随着CuZnMgAl-X体系层间阴离子电负性的减弱, 电子逐渐从层间阴离子向层板发生转移, 主客体间静电作用力逐渐减小, 氢键强度逐渐降低, 禁带宽度逐渐变窄, 体系电子更易向高能级发生跃迁, 稳定性逐渐下降. 此外, Cu的掺杂使得CuZnMgAl-X 体系的价带顶向高能量处发生偏移, 禁带宽度较传统水滑石体系更窄,稳定性更低, 进一步解释了含铜水滑石较难合成的原因.     

Functional Properties of Extruded Nanocomposites Based on Cassava Starch,Polyvinyl Alcohol and Montmorillonite

Summary: The objectives of this work were to produce expanded nanocomposites based on cassava starch, polyvinyl alcohol (PVA) and sodium montmorillonite (Na-MMT). The nanocomposites were characterized according to their expansion index (EI), density, water absorption capacity (WAC), mechanical properties and crystallinity. The nanocomposites were prepared in a single-screw extruder using different starch contents (97.6–55.2 g/100 g formulation), PVA (0–40 g/100 g formulation) and Na-MMT (0–4.8 g/100 g formulation). Glycerol (20 g/100 g formulation) was used as plasticizer. The addition of Na-MMT and PVA resulted in an increase of EI and mechanical strength of the foams. Na-MMT and PVA addition resulted in less WAC of the samples. The studied processing conditions resulted in a good nanoclay dispersion, leading to the formation of an intercalated structure.     

Polymeric herbicide–Montmorillonite composite: synthesis,characterization and release studies

The production of polymeric herbicide intercalated onto montmorillonite interlayer through the process of cation exchange, in order to produce chemically bound polymeric herbicide with clay, has been reported. This was carried out by cation exchange of clay with onium salts of preformed polymeric pentachlorophenyl methacrylate. The products were characterized by various techniques including IR spectroscopy and elemental microanalysis. The interlayer spacing was determined by X‐ray diffraction and thermogravimetric analysis (TGA) and calcination investigated the thermal stability. The morphology of the composite was investigated by scanning electron microscopy. The swelling behaviors in different solvents and release of pentachlorophenol (PCP) in different medium have been described. Copyright © 2001 John Wiley & Sons, Ltd.