Shear-induced change of phase morphology and tensile property in injection-molded bars of high-density polyethylene/polyoxymethylene blends

It is feasible to control the phase morphology and phase inversion for immiscible polymer blends to manipulate their properties. In this work, the blend of high-density polyethylene (HDPE)/polyoxymethylene (POM) was used as an example, to demonstrate the effect of shear on the phase morphology and resultant mechanical properties in immiscible polymer blends. To do so, a well defined “in-process morphology control” process during injection molding was conducted. That was: after making the blends via melt mixing, the injection-molded bars were prepared via a so-called dynamic packing injection molding equipment to impose a prolonged shearing on the melts during the solidification stage. Phase morphologies and crystal structures of the blends were estimated mainly through scanning electron microscopy, differential scanning calorimetry and 2D wide-angle X-ray scattering, respectively. For in-process morphology controlled samples, co-continuous structures, especially subinclusions inside another continuous phase induced by shear, were observed when the HDPE content was between 30 wt% and 50 wt%, leading to much early occurrence of phase inversion and also the lowest degree of orientation for both HDPE and POM. However, for samples obtained via conventional injection molding, a droplet morphology was always observed with HDPE dispersed in POM as the content of HDPE was up to 30 wt%, but with POM dispersed in HDPE as the content of HDPE was 50 wt%. The performances of injection-molded bars were mainly respect to the phase morphologies for samples obtained via conventional injection molding in which tensile properties continuously decreased with increasing of HDPE content up to 30 wt% and then increased with further increasing of HDPE content. For the in-process morphology controlled samples, the tensile properties depended not only on the phase morphology, but more importantly on the degree of orientation. One observed only a slight decrease of tensile property as the content of HDPE was less than 15 wt%, while an abrupt decrease when the content of HDPE was between 30 wt% and 50 wt%, probably due to the lowest degree of orientation in this composition range.     

热－塑变形局部化的有限元分析及其对激光破坏效应的应用

本文给出了热力耦合的热弹粘塑性材料的有限元分析方法，并讨论与之相关的时间积分算法，为改善线性插值函数所引起的不协调性及提高运算速度，应力协调迭代理论被引入相应的算法及程序中，最后对非绝热过程中热－塑变形局部化及激光诱导的剪切变形集中进行了数值模拟，其结果与理论分析有良好的吻合．     

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.     

Small-angle X-ray scattering study of a poly(oxyphenylethylene)–poly(oxyethylene) diblock copolymer gel under shear flow

 The structure and flow behaviour of a micellar “cubic” phase is studied, using small-angle X-ray scattering (SAXS) and constant stress rheometry on a poly(oxyphenylethylene)–poly(oxyethylene) diblock copolymer in water. The predominant structure is a face-centred cubic (fcc) array of spherical micelles, which under shear undergoes layer sliding to give a scattering pattern from stacked hexagonal close-packed layers. A detailed analysis of the SAXS data indicates the presence of a fraction of grains with a structure distorted from a fcc phase. The additional reflections that characterize this structure can be indexed to a rhombohedral unit cell, space group R3ˉm, with the same volume as the fcc unit cell. The rhombohedral unit cell corresponds to a cubic cell that has been “stretched” along a [111] direction, and it is suggested that such a structure results from the gradient in shear velocity in the Couette cell employed. Shearing at high shear rates leads to a “smearing out” of the reflections, but upon cessation of shear under these conditions a highly oriented SAXS pattern is obtained, which confirms the persistence of rhombohedral ordering. The shear-induced changes in orientation are correlated to a plateau observed in the stress plotted against shear rate, such a plateau being a sign of inhomogeneous flow. Received: 8 September 2000 Accepted: 29 November 2000     

Formation and morphology of “shish-like” fibril crystals of aliphatic polyesters from the sheared melt

We found the formation of “shish-like” fibril crystals of aliphatic polyesters such as poly(l-lactic acid) (PLLA), poly(ε-caprolactone) (PCL), poly(12-hydroxydodecanoic acid) (PHDA) and poly(16-hydroxyhexadecanoic acid) (PHHA) from the sheared melt with shear rate  = 5 s⁻¹ observed by polarizing optical microscope (POM). The melting temperature T_ms of obtained fibril crystals of PLLA and PCL were higher than those of spherulites and were close to the equilibrium melting temperature . The small angle X-ray scattering (SAXS) patterns from the bulk sample including fibril crystals, small amount of unoriented small crystals and amorphous showed no peaks arose from the existence of long periods in fibril crystals. These are the evidence that the observed fibril crystals consist of assemblies of a lot of extended chain crystals (ECCs). We observed the morphology of moderately extracted single strand of fibril crystals at the magnification of POM by means of scanning electron microscope. We found that macroscopic fibril crystals of PLLA with diameter d = 10 μm consist of the bundle structure of microscopic fibril crystals with d = 2 μm. From POM observation of the formation of fibril crystals of PLLA and PCL, we showed phase diagrams of molecular weight M and crystallization temperature T_c for the formation of fibril crystals. From these phase diagrams, we evaluated a critical M and T_c for the formation of fibril crystals. Moreover, from the sequential melting and crystallization experiments, it was implied that the entanglement and transesterification play an important role on the formation of fibril crystals of aliphatic polyesters.     

高光谱成像技术的三文鱼多品质指标的预测与分布可视化研究

采用颜色、剪切力和K值评价冰鲜与冻融三文鱼的品质,利用高光谱成像技术结合化学计量学方法对三个品质指标进行预测,并讨论了不同波长选择算法所建模型的预测效果.准备不同冻融次数三文鱼样本,进行高光谱数据采集和品质指标真实值的测定.采用六种预处理方法减少光谱数据中暗电流以及噪声的干扰,采用竞争性自适应重加权算法(CARS)、区...     

Liquid in a tube oscillating along its axis

The Quartz Crystal Microbalance with Dissipation (QCM-D) sensing technique has become widely used to study various supported thin films and adsorption of biological macromolecules, nanoparticles, aggregates, and cells. Such sensing, based on tracking shear oscillations of a piezoelectric crystal, can be employed in situations which are far beyond conventional ones. For example, one can deposit tubes on the surface of a sensor, orient them along the direction of the sensor surface oscillations, and study liquid oscillations inside the oscillating tubes. Herein, we illustrate and classify theoretically the regimes of liquid oscillations in this case. In particular, we identify and scrutinize the transition from the regime with appreciable gradients along the radial coordinate, which are qualitatively similar to those near the oscillating flat interface, to the regime where the liquid oscillates nearly coherently in the whole tube. The results are not only of relevance for the specific case of nanotubes but also for studies of certain mesoporous samples.     

Shear Viscosity of Dilute Polymer Solutions Compared and Contrasted with Mechanical Properties of Nylon Plus Plasticizer

Abstract

Both the shear viscosity η(c) of dilute polymer solutions and Young's modulus Y(c) of nylon plus plasticizer with concentration c are assumed to be expressible as a power series in concentration. Scaling arguments are then presented which reveal an intimate relation between the coefficients of O(c) and O(c²) terms in both η(c) and Y(c) The coefficient of the O(²) term is predicted always to be positive, while that of the O(c) term can in principle have either sign. Comparison with experiment is made for η(C) and Y(c) Some further experiments are proposed for both Y(c) and η(c)     

Cavitation microstreaming and stress fields created by microbubbles

Cavitation microstreaming plays a role in the therapeutic action of microbubbles driven by ultrasound, such as the sonoporative and sonothrombolytic phenomena. Microscopic particle-image velocimetry experiments are presented. Results show that many different microstreaming patterns are possible around a microbubble when it is on a surface, albeit for microbubbles much larger than used in clinical practice. Each pattern is associated with a particular oscillation mode of the bubble, and changing between patterns is achieved by changing the sound frequency. Each microstreaming pattern also generates different shear stress and stretch/compression distributions in the vicinity of a bubble on a wall. Analysis of the micro-PIV results also shows that ultrasound-driven microstreaming flows around bubbles are feasible mechanisms for mixing therapeutic agents into the surrounding blood, as well as assisting sonoporative delivery of molecules across cell membranes. Patterns show significant variations around the bubble, suggesting sonoporation may be either enhanced or inhibited in different zones across a cellular surface. Thus, alternating the patterns may result in improved sonoporation and sonothrombolysis. The clear and reproducible delineation of microstreaming patterns based on driving frequency makes frequency-based pattern alternation a feasible alternative to the clinically less desirable practice of increasing sound pressure for equivalent sonoporative or sonothrombolytic effect. Surface divergence is proposed as a measure relevant to sonoporation.     

Bending analysis of a functionally graded rotating disk based on the first order shear deformation theory

The theoretical formulation for bending analysis of functionally graded (FG) rotating disks based on first order shear deformation theory (FSDT) is presented. The material properties of the disk are assumed to be graded in the radial direction by a power law distribution of volume fractions of the constituents. New set of equilibrium equations with small deflections are developed. A semi-analytical solution for displacement field is given under three types of boundary conditions applied for solid and annular disks. Results are verified with known results reported in the literature. Also, mechanical responses are compared between homogeneous and FG disks. It is found that the stress couple resultants in a FG solid disk are less than the stress resultants in full-ceramic and full-metal disk. It is observed that the vertical displacements for FG mounted disk with free condition at the outer surface do not occur between the vertical displacements of the full-metal and full-ceramic disk. More specifically, the vertical displacement in a FG mounted disk with free condition at the outer surface can even be greater than vertical displacement in a full-metal disk. It can be concluded from this work that the gradation of the constitutive components is a significant parameter that can influence the mechanical responses of FG disks.