(CH3)2N(C6H4)nCN系列分子二阶非线性光学系数的理论研究

在AM1和INDO/CI方法的基础上, 用自编程序计算了(CH3)2N(C6H4)nCN(n=1→6)系列分子的二阶非线性光学系数β~i~j~k和β~μ并系统地研究了共轭链长对分子二阶非线性光学系统的影响及β~μ对激光场频率的依赖关系(色散效应)     

固体表面能色散成分的测定

Tamai, Hamilton, Carre等曾通过测量烷烃-水双液参照体系在固体表面的接触角,采用基于界面非色散成份的均方关系, 计算了高表面能固体的表面能色散成份(γs^d)及非色散成份(γs^p), 对此计算方法, Fowkes曾给予批评, 提出界面能的非色散成份主要来源于酸碱配位作用, 基于非色散成份均方关系的计算不能正确反映实际情况, 本研究改进了由双液法接触角值计算γs^d值的方法。     

WO3在γ-Al2O3表面的分散状态和最大分散量

应用X光衍射法(XRD)测定了WO2/γ-Al2O3体系的物相组成和平均晶粒度,以及该体系的孔容和比表面:应用XRD相定量外推法和光电子能谱(XPS)峰强度比(Iw4f/IA12s)法定量测定了WO3在γ-Al2O3表面的最大分散量,测值分别为0.21和0.20gWO3/100m[2]γ-Al2O3,与按照WO3在γ-Al2O3表面作密置单层排布模型的计算值0.189WO3/100m[2],即4.9x10[18]W原子/m[2])相近,对WO3/γ-Al2O3体系与MoO3/γ-Al2O3体系比较和讨论。     

二到七环多苯稠合物的三阶非线性光学效应的理论 研究

利用含组态相互作用的INDO－SDCI和态求和(SOS)方法,计算二到七环的稠合多苯化合物的三种不同物理过程的频率相关的三阶非线性光学系数。讨论不同光物理过程的色散行为及π电子离域程度对非线性光学效应的影响,同时给出计算简并四波混合(DFWM)的非线性光学系数的具体表达式。计算结果表明,三阶非线性光学系数随着环沿一维方向扩展而急剧增加,π-π^*电荷转移对多苯稠合物的三阶非线性极化率起主要贡献。     

THE EFFECT OF CLAY DISPERSION ON THE CRYSTALLIZATION AND MORPHOLOGY OF POLYPROPYLENE／CLAY COMPOSITES

PP/clay composites with different dispersions, namely, exfoliated dispersion, intercalated dispersion and agglomerates and particle-like dispersion, were prepared by direct melt intercalation or compounding. The effect of clay dispersion on the crystallization and morphology of PP was investigated via PLM, SAXS and DSC. Experimental results show that exfoliated clay layers are much more efficient than intercalated clay and agglomerates of clay in serving as nucleation agent due to the nano-scale dispersion of clay, resulting in a dramatic decrease in crystal size (lamellar thickness and spherulites) and an increase of crystallization temperature and crystallization rate. On the other hand, a decrease of melting temperature and crystallinity was also observed in PP/clay composites with exfoliated dispersion, due to the strong interaction between PP and clay. Compared with exfoliated clay layers, the intercalated clay layers have a less important effect on the crystallization and crystal morphology. No effect is seen for samples with agglomerates and particle-like dispersion, in regard to melting temperature, crystallization temperature, crystal thickness and crystallinity.     

Preparation of Silica/Poly(divinylbenzene) Composite Particles by Dispersion Polymerization in Supercritical Carbon Dioxide

Silica/poly(divinylbenzene) (PDVB) composite particles were synthesized by the dispersion polymerization of divinylbenzene (DVB) with ultrafine silica particles in supercritical carbon dioxide (scCO₂). Silica particles of average diameter 130 nm were pretreated with 3-(trimethoxysilyl) propyl methacrylate in order to be well dispersed in CO₂ and participated in the polymerization. Random copolymeric dispersant, poly(diisopropylaminoethyl methacrylate-co-heptafluorobutyl methacrylate) was used as a stabilizer to provide sufficient stabilization to latexes in scCO₂ and the silica/PDVB composite powder was obtained in high yield from the polymerization. SEM analysis revealed that the composite particles prepared at 5% silica loading ratio and 6% stabilizer concentration with respect to monomer have the average diameter of 1.60 μm with uniform and spherical morphology. The composites were also characterized by FTIR spectroscopy and TGA.     

Influence of surface treatment on mechanical behaviour of fumed silica/epoxy resin nanocomposites

The present paper shows the potential of fumed silica as nano-reinforcements in polymers, by considering the limitations and challenges one has to face dealing with nanoparticles in general. The dominating effect of the manufacturing route and surface properties of fumed silica influencing the resulting degree of dispersion and the interfacial adhesion were investigated by electron microscopy (TEM, SEM). The resulting (fracture-) mechanical properties of the fumed silica/epoxy composites were investigated for volume contents of 0.5 vol% and below. Independent of the surface modification, static and dynamic modulus decreased slightly by adding the fumed silica. Hence, the fracture toughness K _Ic turned out to be significantly increased (54%) adding only 0.5 vol% of surface modified fumed silica.     

Alkoxysilane-Functionalized Silica Fillers — Preparation and Characterization

A number of new silica fillers have been obtained in the emulsion system and changes in their surface properties appearing as a result of modification with the following alkoxysilanes have been evaluated: [3-(phenylamino)propyl]trimethoxysilane (PhAPS), (3-glycidoxypropyl)trimethoxysilane (GPS), N-2-(aminoethyl)-3-aminopropyltrimethoxysilane (AEAPS), 3-mercaptopropyltrimethoxysilane (McPS) and octyltriethoxysilane (OS). Functionalization of SiO₂ surface has been made with different amounts of the modifiers. The fillers have been characterized by determination of their dispersion, adsorption abilities, morphological and chemical properties (effectiveness of modification and hydrophobization determined by wetting and sedimentation methods). The silica-based fillers obtained have been made of spherical shaped particles characterized by high size uniformity (low polydispersity index) of the mean diameter within the range 440–520 nm. The fillers show limited hydrophilic properties as confirmed by the wettability and sedimentation tests in water.     

Study on Dispersion of TiO2 Particles During Polymerization of PET

An important factor influencing the stability of colloidal suspension is zeta potential (ζ-potential) on the surface of particles. In this work, ζ-potential of TiO₂ particles in ethylene glycol (EG) with various additives for poly(ethyleneterephthalate) (PET) polymerization, such as metallic salts, phosphoric acid and alkyl phosphates, were investigated by electrophoretic mobility method. The dispersion stability of TiO₂/EG suspension was influenced by decrease in the absolute value of the ζ-potential by the addition of metal acetates as well as phosphates. The addition of triethylamine (TEA) in the TiO₂/EG suspension restrained the change of ζ-potential from negative to positive, which resulted from phosphoric acid. The molar ratio of phosphoric acid to an acetate was found to have an influence on the dispersion ability of TEA in TiO₂/EG suspension. Effect of metallic salts, phosphoric acid and TEA on the stability of TiO₂/EG suspension was studied in the actual polymerization of PET. It was proved that the addition of TEA is highly effective for the dispersion of TiO₂ particles in PET, even in the presence of metallic salts, phosphoric acid and its alkyl phosphates.     

Preparation and characterization of polyethylene/TiO2 nanocomposites

The rheological behaviour, dispersion, crystallization behavior, mechanical properties, fracture surface morphology of polyethylene (PE)/TiO₂ nanocomposites prepared by melt compounding were investigated using rheometer, energy dispersive X-ray spectrometer (EDX), polarized microscopy, impact tester, universal testing machine and field-emission scanning electron microscopy (FE-SEM). The rheological analysis indicated a fine dispersion of TiO₂ during the melt compounding. The large scaled surface dispersion of TiO₂ nanoparticles was revealed by the EDX composition distribution maps. The introduction of 2.0 wt% TiO₂ in composites improved the mechanical properties significantly compared to neat PE, and resulted in 45% increase in notched impact strength. Moreover, the further analysis and discussion showed the mechanical properties of the composites were controlled by the dispersion conditions of TiO₂ and its nucleating effect on PE crystallization.