Nonlinear dynamic analysis of dielectric elastomer membrane with electrostriction

The dielectric elastomer (DE) is an important intelligent soft material widely used in soft actuators, and the dynamic response of the DE is highly nonlinear due to the material properties. In the DE, electrostriction denotes the deformation-dependent permittivity. In the present study, we formulate the nonlinear dynamic governing equations of the DE membrane considering the electrostriction effect. The free vibration and parametric excitation of the DE membrane with different geometric sizes are calculated. The free vibration bifurcations induced by the initial location and the voltage are both discussed according to an energy-based approach. The amplitude-frequency characteristics and bifurcation diagrams of parametric excitation are also given. The results show that electrostriction decreases the free vibration amplitude and increases the frequency, but it has less influence on the parametric excitation oscillation frequency and decreases the parametric excitation amplitude except when the membrane resonates. The initial location and the applied voltage can induce the snap-through instability of the free vibration. A large geometric size will lead to a much lower resonance frequency. The resonance amplitudes increase while the resonance frequencies decrease with the increase in the applied voltage. The critical voltage of snap-through instability for the parametric excitation is larger than that for the free vibration one.

     

Global existence of strong solutions to micropolar equations in cylindrical domains

The micropolar equations are a useful generalization of the classical Navier–Stokes model for fluids with microstructure. We prove the existence of global and strong solutions to these equations in cylindrical domains in . We do not impose any restrictions on the magnitude of the initial and external data, but we require that they cannot change in the x₃‐direction too fast. Copyright © 2014 John Wiley & Sons, Ltd.     

用液芯柱透镜快速测量液相扩散系数-折射率空间分布瞬态测量法

本文提出了一种快速测量液相扩散系数的方法, 该方法以液芯柱透镜作为液相扩散池和成像元件, 利用柱透镜成像过程中特有的折射率空间分辨测量能力, 只需记录一幅瞬态扩散图像, 根据图像的像宽与折射率的对应关系, 基于扩散定律快速计算出液相扩散系数. 实验研究了室温(25℃)下乙二醇和纯水间的扩散过程, 用折射率空间分布法测量了扩散系数, 和其他测量方法得到的结果进行了分析对比, 结果表明:用折射率空间分布法测量液相扩散系数具有数据采集耗时短(～20 ms)、测量速度快(<1 s)、精度高(相对误差<3%)和操作简单的特点, 为快速测定液相扩散系数提供了一种有效的新方法.     

一个新的自由能函数对介电高弹薄膜的多组等双轴预拉伸下力电耦合实验的预测

当介电高弹聚合物薄膜被施以面内等双轴预拉伸后, 受到厚度方向的电压作用时, 薄膜在力场和电场共同作用下产生大变形. 电场采用Maxwell应力分析, 力场采用橡胶弹性模型分析. 拟合这类变形的常用橡胶弹性模型主要有Neo-Hookean, Arruda-Boyce, Gent等模型. 这些模型对实验数据的定量拟合存在不同程度的偏差. 通过对实验数据的分析, 结合数学方法, 提出了一个新的自由能函数模型. 通过该模型对VHB4905介电高弹聚合物薄膜的多组等双轴预拉伸电力耦合实验进行拟合, 并以Neo-Hookean, Gent模型作为对照, 结果与实验数据拟合很好, 比对照模型的偏差明显缩小.     

Poly(meth)acrylate grafted EPDM via reverse atom transfer radical polymerization: A single pot process

This investigation reports a one pot preparation of poly(meth)acrylate grafted EPDM via reverse ATRP and evaluation of their physical and mechanical properties. The graft copolymerization of 2-ethylhexyl acrylate and methyl methacrylate was carried out from EPDM using reverse ATRP in toluene at 90 °C using CuBr₂ as catalyst in combination with PMDETA as ligand and AIBN as thermal initiator. The grafted EPDMs were separated from the reaction mixture, purified and then characterized by FT-IR, ¹H NMR, DMA and TGA analyses. Surface energies and tensile properties were evaluated by Goniometer and UTM respectively. Acrylate grafted EPDMs showed better thermal stability, better tensile property, whereas methacrylate grafted EPDMs showed higher surface energy and better oil resistance property than the pristine EPDM. Surface morphologies of grafted EPDMs were analyzed by AFM and SEM analyses. This one pot grafting approach led to very high grafting percentage without undesirable homopolymerization and gelation.     

Use of wollastonite in a thermoplastic elastomer composition

Thermoplastic elastomer compositions (TPEs) based on wollastonite-filled SEBS/PP/oil blends were prepared and characterized. The development of new TPEs with improved mechanical strength may broaden their applications, especially for soft goods. Wollastonite is a natural filler that combines high thermal stability with low health hazard in comparison to other fibrous inorganic fillers. Morphological, thermal and mechanical properties of the composite materials were studied by transmission electron microscopy (TEM), thermogravimetry (TGA), tensile tests and dynamic mechanical analysis (DMA). The results indicate that the filler was mainly distributed as nanoparticles in the PS domains, improving the mechanical resistance of the materials even at low concentration (2 phr).     

A novel approach for preparation of conductive hybrid elastomeric nano‐composites

Since the discovery of carbon nanotubes (CNTs) and intrinsically conductive polymers, such as polyaniline (PANI) some research has focused on the development of novel hybrid materials by combining CNT and PANI to achieve their complementary properties. Electrically conductive elastomer nano‐composites containing CNT and PANI are described in the present investigation. The synthesis procedure includes in‐situ inverse emulsion polymerization of aniline doped with dodecylbenzene sulfonic acid in the presence of CNT and dissolved styrene‐isoprene‐styrene (SIS) block copolymer, followed by a precipitation–filtration step. The synthesis step is carried out under ultrasonication. The resulting uniform SIS/CNT/PANI dispersions are stable for long time durations. The incorporation of CNT/PANI in the SIS elastomeric matrix improves thermal, mechanical and electrical properties of the nano‐composites. The formation of continuous three‐dimensional CNT/PANI network, assumed to be responsible for enhancement of the resulting nano‐composite properties, is observed by HRSEM. A relatively low percolation threshold of 0.4 wt.% CNT was determined. The Young's modulus of the SIS/CNT/PANI significantly increases in the presence of CNT. High electrical conductivity levels were obtained in the ternary component systems. Copyright © 2013 John Wiley & Sons, Ltd.     

Ordered nanostructures from self-assembly of rod–coil oligomers with n-shaped rod and dendritic poly(ethylene oxide) coil segment

The n-shaped rod–coil molecules consisting of an anthracene unit and two biphenyl groups connected by acetylenyl bonds as a conjugated rod segment and dendritic poly(ethylene oxide)s with different cross-sectional areas were synthesised. These new molecular structures were characterised by using ¹H NMR and MALDI-TOF-MS. The self-assembly of these molecules in the bulk state and in aqueous solution was investigated using differential scanning calorimetry, X-ray diffraction and transmission electron microscopy (TEM). In the bulk state, molecule 1a with a linear coil segment, self-organised into lamellar crystalline structures, whereas molecules 1b and 1c with di- and tetra-branched dendritic wedges did not solidify at room temperature. Dynamic light scattering and TEM experiments reveal that in aqueous solution, the molecules exhibit a strong tendency to organise into the thread-like fibres along the axial direction of cylindrical micelles or into the wide fibroid bundles via the aggregation of cylindrical micelles as the cross-sectional area of the dendritic coil segments increases.     

木质素基生物质聚氨酯

聚氨酯材料是由多元醇与异氰酸酯经过聚加成反应得到的一种多功能性的高分子材料,在涂料、弹性体、胶黏剂、泡沫等领域具有非常广泛的应用。但是多元醇与异氰酸酯都来源于石油,随着石油资源的消耗以及环境问题的加剧,寻求可再生原料成为研究热点。目前对于生物基聚氨酯的报道,大多都是针对多元醇的生物质替代,其中利用最多的是植物油和木质素。木质素作为储量丰富的天然有机碳资源,当前利用效率极低,大多被作为燃料而浪费。与植物油相比,在合成聚氨酯方面木质素不存在“与人争粮”问题并且相关产品性能优越,但是木质素的利用仍存在一定缺陷,如分离困难、均一性差、易聚集、位阻大和活性低等,这让木质素的直接利用或改性利用成为关键。本文主要介绍了木质素在生物基聚氨酯合成中的发展现状和最新研究进展。最后,在此基础上展望了木质素基聚氨酯材料在不同领域的发展前景。