聚倍半硅氧烷以不同方式改性纤维素绝缘纸的机理研究（英文）

本文运用分子动力学方法,建立了纯纤维素模型和一系列聚倍半硅氧烷以不同方式改性的纤维素绝缘纸模型,并对其热力学性能进行了计算、对比和讨论.实验结果表明,各聚倍半硅氧烷纤维素改性模型的性能均优于未改性模型,并且当两条纤维素分子链作为取代基通过化学键接枝在聚倍半硅氧烷分子上(M2模型)时,改性效果最佳,其内聚能密度与溶解度参数的值相较于未改性模型提高了9%,拉伸模量、体积模量、剪切模量、柯西压的值分别提升了38.6%、29.5%、41.1%和29.5%,此外本文还计算并分析了各模型的自由体积分数和均方位移,结果显示,相较于其他模型,M2模型中的化学键在避免使纤维损失强度的同时,增加了分子链间的纠缠,使纤维素分子链占据了更多自由体积,从而使体系具有更小的自由体积分数,抑制了纤维素的链运动,进而提升了纤维素绝缘纸的热稳定性,这从微观角度解释了化学处理影响改性效果的机理.     

TiO_2掺杂粒度对纤维素强度和热稳定性影响的分子模拟研究

变压器绝缘纸的主要成分为纤维素,为了提升绝缘纸的强度和热稳定性,利用纳米TiO_2掺杂纤维素,通过分子模拟方法研究不同纳米TiO_2粒度掺杂纤维素的强度和热稳定性.研究表明,纳米TiO_2使得纤维素强度提高,拉伸模量增大,抗形变能力增强,体积模量与剪切模量比值(K/G)增大,纤维素韧性增强;纳米TiO_2表面羟基与纤维素形成新的氢键网络使得径向分布函数峰值增大,复合体系更加稳定,其热稳定性增强.掺杂比例相同时,随着纳米TiO_2粒度减小,拉伸模量和柯西压增大,泊松比减小,纤维素的抗形变能力增强;纳米TiO_2表面羟基占有率越高,纳米TiO_2与纤维素越易形成氢键抑制纤维素链运动,纳米TiO_2也减小复合体系的自由体积,使得复合体系结构更加稳定,热稳定性更强.因此,掺杂小纳米TiO_2粒度是提升纤维素强度和热稳定性有效的方法.     

纳米SiO_2掺杂对有水环境下间位芳纶绝缘纸性能影响的研究

为了进一步了解SiO_2纳米粒子掺杂对有水环境下间位芳纶绝缘纸性能的影响以及有、无水环境下芳纶绝缘纸性能的变化,本文利用分子动力学的方法建立了有水存在的芳纶分子模型、经SiO_2纳米掺杂后的芳纶分子模型以及无水参与的芳纶分子模型,研究了SiO_2纳米掺杂和水分对芳纶绝缘纸在玻璃转化温度、均方位移及力学模量方面的影响.研究结果表明,水分的存在使得芳纶绝缘纸的玻璃转化温度由原先的549 K降为523 K,在此基础上进行纳米SiO_2掺杂后玻璃转化温度可以由523 K提升到530 K.与无水环境芳纶绝缘纸的均方位移相对比可以发现,水分的存在在一定程度上提高了芳纶分子的链运动进而削弱了绝缘纸的热稳定性,而SiO_2纳米改性可以减弱水分对芳纶绝缘纸的这种不利影响.改性后的绝缘纸在有水环境下的力学性能得以提升,通过对比有、无水环境下芳纶绝缘纸的力学模量可以发现,一定水分的加入反而使得绝缘纸的力学性能得到了一定的提升.最后对所得模拟结果进行了理论分析,为提升芳纶绝缘纸的性能提供了有益的参考.     

硅氧烷改性水性聚氨酯的制备及性能

用聚氧化丙烯二醇、聚醚接枝聚硅氧烷、甲苯二异氰酸酯、二羟甲基丙酸和1,4丁二醇进行聚合,并通过三乙胺直接水乳化法合成了一种新型硅氧烷改性的透明且稳定性好的水性聚氨酯乳液.用Fourier变换红外光谱、化学分析电子能谱、接触角仪、电子拉力试验机以及乳液稳定性测试对其进行研究,测试表明乳液稳定性好,聚硅氧烷链段已被化学键入聚氨酯分子链中,硅氧烷在乳胶膜表明富集,对聚氨酯材料有明显的表面改性作用.研究结果还表明,经少量硅氧烷改性的聚氨酯材料本体的力学性质变化不大,仍然是一种很好的弹性体.随着硅氧烷含量的增加,抗张强度提高,但断裂伸长率有所减小.     

超支化高分子桥联聚倍半硅氧烷复合物的NMR研究

以三羟甲基丙烷(TMP)为内核,二羟甲基丙酸(DMP)为支化单元用准一步法合成了重均分子量为12100的第四代端羟基脂肪族超支化聚酯(HBPE-G4),用3-异氰酸酯基丙基三乙氧基硅烷(TPIC)对它进行了端基改性,并以其为桥联剂,与聚倍半硅氧烷(PMSQ)复合制备出超支化高分子桥联聚倍半硅氧烷复合物．利用固体核磁共振(NMR),傅立叶红外(FI-IR),分子纳米粒度分析等方法表征了改性超支化高分子和复合物的结构和反应程度,并通过测量¹³C T₁,¹H T₂,¹H T_1ρ研究了体系中各组分的运动性能,以及超支化高分子与聚倍半硅氧烷之间的相容性．     

用于KDP晶体的桥式聚倍半硅氧烷防潮膜

 以间苯亚甲基二异氰酸酯与氨丙基三乙氧基硅烷反应制备了具有长桥链结构的聚倍半硅氧烷前驱体,利用制备的前驱体在碱性条件下水解缩聚制备了桥式聚倍半硅氧烷溶胶,并采用提拉浸涂法对磷酸二氢钾（KDP）晶体镀膜。通过1H NMR 对前驱体进行结构定性,利用²⁹Si MAS NMR和N₂吸附-脱附表征对凝胶结构进行了分析,用AFM对薄膜的表面形貌进行了研究,通过湿度为60%时KDP晶体光学性质的变化考察了薄膜的防潮性能。利用三倍频和基频激光测试了薄膜的抗激光损伤性能。结果表明:这种桥式聚倍半硅氧烷薄膜对KDP晶体具有很好的防潮保护作用,并显示了较好的抗激光损伤性能。     

笼形倍半硅氧烷NMR的研究

笼形倍半硅氧烷是一类典型的多面体有机-无机分子复合物. ²⁹Si NMR是测定这类含硅化合物结构的有效方法. 利用²⁹Si NMR对6种笼形八聚倍半硅氧烷的结构进行了研究,结合所得数据探讨了这类化合物中取代基电负性对²⁹Si NMR化学位移的影响.根据¹H,¹³C NMR数据及各峰归属可以进一步判断笼形倍半硅氧烷取代基R的类型和结构.     

苝聚集体随机激光的近场散射增强

本文通过物理模拟发现苝聚集体纳米粒子有很强的近场散射. 苝聚集体由异丁基取代聚倍半硅氧烷(POSS)苝(DPP)构成,其理论模拟得到的近场散射增强被实验证实. 同时,由聚集体的二硫化碳溶液激发出相干随机激光. 近场增强源自于通过化学键连接的POSS基团,相干随机激光源自于苝发射团. 本文通过分子设计发展出一种新的随机激光体系,为后续一系列交叉研究打开了大门,相关交叉研究主要涵盖无序光子学的分子设计等领域.     

苝聚集体随机激光的近场散射增强（英文）

本文通过物理模拟发现苝聚集体纳米粒子有很强的近场散射.苝聚集体由异丁基取代聚倍半硅氧烷(POSS)苝(DPP)构成,其理论模拟得到的近场散射增强被实验证实.同时,由聚集体的二硫化碳溶液激发出相干随机激光.近场增强源自于通过化学键连接的POSS基团,相干随机激光源自于苝发射团.本文通过分子设计发展出一种新的随机激光体系,为后续一系列交叉研究打开了大门,相关交叉研究主要涵盖无序光子学的分子设计等领域.     

电场和温度对聚合物空间电荷陷阱性能的影响

模拟分子的结构和行为有助于更深刻地分析空间电荷陷阱性能变化的微观机理.利用Materials studio软件建立聚乙烯模型,通过分子链段运动产生的能量和自由体积变化对微观结构和电荷陷阱进行分析.结果表明:温度由298 K逐渐升高至363 K的过程中,聚合物分子热运动加剧导致的滑移扩散现象,使自由体积和陷阱能级在363 K处分别出现1542.07 ~3和0.66 eV的最大值和最小值.然而在Z轴方向施加0.0007 Hartree/Bohr(1 Hartree/Bohr=5.2×10~(11)V/m)电场作用时,由于电致伸缩产生Maxwell应力,使分子链段出现局部有序排列,增大范德瓦耳斯能至-360.18 kcal/mol(1 kcal/mol=4.18 kJ/mol),而自由体积降低了279.77 ~3,导致陷阱能级减小0.45 eV.当363 K和0.0007 Hartree/Bohr联合作用时,聚乙烯的陷阱能级相比同温无电场作用降低0.17 eV.分子模拟结果与实测结果相符.利用分子热运动和电致伸缩效应,初步探讨了材料自由体积和范德瓦耳斯相互作用能变化的微观机理,证实分子链段运动改变了微观结构,从而影响电荷陷阱特性.并且与温度相比,电场作用会使材料产生更低能级的空间电荷陷阱.     

基于多链模型的磁流变弹性体剪切模量的数值分析

从颗粒间的磁相互作用能出发,利用磁能密度的变化,计算了磁流变弹性体的磁致剪切模量.考虑了链内颗粒和相邻链中颗粒的影响,修正了磁流变弹性体的磁偶极子模型.构建了 BCT 结构计算模型,对含柱状结构的磁流变弹性体进行了计算.计算结果表明,传统的点偶极子模型高估了磁流变弹性体的磁致剪切模量；在提高磁流变弹性体的磁致剪切模量方面,颗粒体积比浓度较小时,链状结构比柱状结构要好；而当颗粒体积比浓度较大时,柱状结构优于链状结构.     

Effects of Carbon Black on Chain Mobility and Dynamic Mechanical Properties of Solution Polymerized Styrene-Butadiene Rubber

The structure of the bound rubber, the ¹H NMR (nuclear magnetic resonance) relaxation time, and the crosslink density of the physical network and the glass transition, were studied for solution polymerized styrene-butadiene rubber (SSBR) filled by carbon black, to investigate the effects of carbon black on the chain mobility and dynamic mechanical properties. It was found by ¹H NMR analysis that the rubber chains were adsorbed on the surface of carbon black to form physical crosslinks and restrict the mobility of the chains, especially for some high-mobility units such as chain ends. It was calculated, according to the molecular weight between adjacent crosslinks, that the main motion units of the tightly adsorbed chains appeared to be similar in size to the chain segments. The glass transition temperature (T _g) obtained by differential scanning calorimetry (DSC) could not be used to judge the effect of carbon black on chain mobility, while the appearance and change of the loss-tangent (tan δ) peak at high temperature in dynamic mechanical thermal spectrometry (DMTS) test showed that there were three chain states: free chains, loosely adsorbed chains, and tightly adsorbed chains. The dynamic rheology test showed that the unfilled SSBR compound had the rheological characteristics of entangled chain networks; however the nonlinear viscoelasticities of the filled SSBR were related to the gradual disentanglement of adsorbed chains and free chains. The peaks in tan δ vs. temperature curves implied that the motion unit size decreased with the increase of bound rubber content, and the modulus vs. temperature curve showed an apparently lower mobility of adsorbed chains than that of free chains through the very low dependence of modulus on temperature for the highly filled compounds. The extremely high tensile modulus of the vulcanizate with 63.6% carbon black at room temperature also implied that the adsorbed chains were in the glass state due to their restriction by the carbon black.     

Dependence of particle volume fraction on sound velocity and attenuation of EPDM composites

The sound velocity and the attenuation coefficient of EPDM (Ethylene-propylene Diene Monomer) composites incorporated with Silicon Carbide particles (SiCp’s) of various volume fractions (0-40%) were experimentally and theoretically investigated. For the experiment a through-transmission technique was used. For the theoretical prediction, some mechanical property models such as Reuss model and Coherent Potential Approximation (CPA) model etc. were employed. The experimental results showed that the sound velocity decreased with the increase of the SiCp volume fraction up to 30% and then increased with the 40 vol% specimen. The attenuation coefficient was increased with the increasing SiCp volume fractions. The modified Reuss model with a longitudinal elastic modulus predicted most well the experimental sound velocity and elastic modulus results.     

Preparation of nanocrystalline cellulose via ultrasound and its reinforcement capability for poly(vinyl alcohol) composites

Rod-shaped nanocrystalline cellulose (NCC) was prepared from microcrystalline cellulose (MCC) using the purely physical method of high-intensity ultrasonication. Scanning electron microscopy, transmission electron microscopy, and X-ray diffraction was used for the characterization of the morphology and crystal structure of the material. The thermal properties were investigated using thermogravimetric analysis. The reinforcement capabilities of the obtained NCC were investigated by adding it to poly(vinyl alcohol) (PVA) via the solution casting method. The results revealed that the prepared NCC had a rod-shaped structure, with diameters between 10 and 20 nm and lengths between 50 and 250 nm. X-ray diffraction results indicated that the NCC had the cellulose I crystal structure similar to that of MCC. The crystallinity of the NCC decreased with increasing ultrasonication time. The ultrasonic effect was non-selective, which means it can remove amorphous cellulose and crystalline cellulose. Because of the nanoscale size and large number of free-end chains, the NCC degraded at a slightly lower temperature, which resulted in increased char residue (9.6-16.1%), compared with that of the MCC (6.2%). The storage modulus of the nanocomposite films were significantly improved compared with that of pure PVA films. The modulus of PVA with 8 wt.% NCC was 2.40× larger than that of pure PVA.     

Preparation and Characterization of a Novel Composite of Chitosan/Shell Particles

Nanometer sized (mean size: 433.9 nm) pearl shell particles (SP) were prepared with a ball mill. Thermal analysis and Fourier transform infrared (FTIR) results proved that the SP contained mainly CaCO₃ (about 95%) and a small organic phase (about 5%). Novel biodegradable composites based upon chitosan (CS) and SPs were prepared using an in situ precipitation method. The organic components of SP are highly compatible with both CS and glutaraldehyde (GA). The strength and modulus of CS gel rods, prepared by coagulation of a CS/SP/GA solution in NaOH, in both the dry and wet state, were improved remarkably with addition of appropriate amounts of SP together with GA. For example, with a composition of 3% SP and 0.3% GA added, the strength and modulus were 42.9 MPa and 1.41 GPa, increasing 75 and 464% compared with CS alone, respectively. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) results showed that GA acts as not only a crosslinking agent for CS, but also a compatibilizer for CS and SP. It was found that the modified rods have smaller free volume size but nearly the same free volume fraction as pure CS rods. The good interfacial adhesion and more compact microstructure can sensitively reflect the changes in the free volume of the composites.     

Structural and thermodynamic properties of the restricted primitive model electrolyte in a mixture with uncharged hard spheres: a grand canonical Monte Carlo simulation and integral equation study

A restricted primitive model electrolyte in a mixture with uncharged hard spheres was studied at room temperature using grand canonical Monte Carlo computer simulation and Ornstein–Zernike integral equation theory in the hypernetted chain approximation (HNC). The mean spherical approximation results are also presented for a few cases. We obtained the pair distribution functions of species of the system, the dependencies of the total fluid density and the ionic fraction on the chemical potentials, the excess internal energy and the heat capacity at constant volume for a wide range of chemical potentials of the species from the simulations and HNC theory. In the majority of cases, good agreement between the theoretical predictions and simulation data is obtained. The composition of the mixture is determined by the chemical potentials of both species. The pair distribution functions have a Debye-like shape at low densities for various values of the ion fraction. By increasing the chemical potential of the uncharged component, weak trends for structuring of the solution are observed with the formation of ion-hard sphere-ion complexes. At high densities, a tendency for in-phase oscillations of ion–ion functions is observed similar to the pure electrolyte in the restricted primitive model. We analysed the chemical potential–density and the chemical potential–ion fraction projections of the equation of state in detail. Also, the heat capacity at constant volume has been calculated for the first time. The model and the results are useful for the development of the theory of inhomogeneous fluid mixtures.     

Rheology of nanosized hairy grain suspensions

Suspensions of nanosized hairy grains have been prepared by grafting long polydimethylsiloxane chains (molecular weight ) onto silica particles (radius ), dispersed into a good solvent of PDMS. Depending on the particle volume fraction, different rheological behaviors are observed. In the very dilute regime, the suspensions are perfectly stable and the particles behave almost as hard spheres: flow penetration inside the corona is then very weak. When the particle volume fraction goes to the close packing volume fraction, the suspension viscosity does not diverge as for hard spheres due to the increase of flow penetration inside the corona and to corona entanglements. The particles have then the same behavior as polymer stars having an intermediate number of arms (). Finally, in the concentrated regime (), the suspensions form irreversible gels. We shown that this unexpected gelation phenomenon is related to the presence of the silica cores: grafted PDMS chains can adsorb onto different particles and form irreversible bonds between the cores. The viscosity and elastic modulus evolutions during gelation are well described by the scalar percolation model of sol-gel transition. Received 23 March 1998     

PVP在水/丙酮混合溶剂中分子运动行为的研究

通过对粘度、自旋-自旋弛豫时间以及1H NMR谱的测定,研究了PVP在不同体积配比的水/丙酮溶液中的特性粘数变化和分子运动规律,并讨论了引起这些变化的原因.结果表明:随着丙酮的不断加入,PVP的特性粘数[η]先增加后减小,而T2H先减小后增大.[η]出现最大值也是T2H出现最小值的时候,丙酮的体积百分数为40%.丙酮的加入破坏了水分子间自身氢键相互作用形成的网状结构,解离出来的水分子被PVP优先吸附到大分子链上,部分与羰基形成氢键,另一部分以自由水的形式被包裹在大分子线团内.水分子的不断进入以及与水形成新的氢键使PVP链逐渐伸展,引起特性粘数的增大,分子运动受阻.当丙酮含量增加到一定程度时,水的含量不足以使大分子链继续膨胀,故链呈卷缩状态,使大分子运动逐渐恢复自由.1H NMR谱中各质子的化学位移变化也证实了此过程中的氢键变化规律.     

Density functional theory for molecular orientation of hard rod fluids in hard slits

A density functional theory (DFT) is used to investigate molecular orientation of hard rod fluids in a hard slit. The DFT approach combines a modified fundamental measure theory (MFMT) for excluded-volume effect with the first order thermodynamics perturbation theory for chain connectivity. In the DFT approach, the intra-molecular bonding orientation function is introduced. We consider the effects of molecular length (i.e. aspect ratio of rod) and packing fraction on the orientations of hard rod fluids and flexible chains. For the flexible chains, the chain length has no significant effect while the packing fraction shows slight effect on the molecular orientation distribution. In contrast, for the hard rod fluids, the chain length determines the molecular orientation distribution, while the packing fraction has no significant effect on the molecular orientation distribution. By making a comparison between molecular orientations of the flexible chain and the hard rod fluid, we find that the molecular stiffness distinctly affects the molecular orientation. In addition, partitioning coefficient indicates that the longer rodlike molecule is more difficult to enter the confined phase, especially at low bulk packing fractions.