液晶弹性体的研究进展

综述了液晶弹性体,主要是侧链液晶弹性体、主链液晶弹性体的合成方法,液晶弹性体的热弹性、光弹性、压电性、机械力场下的取向性、溶胀行为以及形变中内能与熵的作用等物理性质,介绍了其在人工肌肉、纳米机械、人工智能、形状记忆等方面的潜在应用前景及最新研究成果.     

多重形状记忆液晶高分子材料

采用化学交联的方法制备了不同交联度的氢键型液晶弹性体,并研究了其多重形状记忆效应。研究表明,当选用刚性交联剂时,随着交联度的提高,材料的软化温度逐渐升高,液晶性能逐渐变弱,此时材料的宽玻璃化转变温度可以作为两重形状记忆效应的调试开关;当选用柔性交联剂时,控制交联剂的比例,利用液晶弹性体的玻璃化转变温度和熔融转变温度,调试了材料的多重形状记忆效应。     

自愈合弹性体的合成及应用研究进展

综述了利用Diels-Alder化学方法、超分子化学方法等制备自愈合弹性体的研究进展,并介绍了自愈合弹性体在形状记忆材料、生物医学材料、液晶材料、电子材料中的应用研究现状。     

反式-1，4-聚异戍二烯／炭黑导电复合材料的形状记忆性能

采用熔融共混法及适度硫化工艺制备了反式-1．4-聚异戊二烯／炭黑导电复合材料．研究了该复合材料的力学性能、导电性、热致及电致形状记忆性能。结果表明．随炭黑用量的增加,复合材料的拉伸强度先增加后减少．拉断仲长率逐渐降低。100％定伸应力和300％定伸应力呈升高趋势;高导电炭黑可大幅提高复合材料的导电性,复合材料的热刺激响应回复温度逐渐升高．热致形变回复率和热致回复速度均降低,热致形状记忆性能降低。复合材料具有良好的电致形状记忆性能．高导电炭黑的用量和外加电压对复合材料的电致形状记忆性能有重要影响．电致形变回复率和回复速度随外加电压或高导电炭黑用量的增加而增加。     

反式-1,4-聚异戊二烯/炭黑导电复合材料的形状记忆性能

采用熔融共混法及适度硫化工艺制备了反式-1,4-聚异戊二烯/炭黑导电复合材料,研究了该复合材料的力学性能、导电性、热致及电致形状记忆性能。结果表明,随炭黑用量的增加,复合材料的拉伸强度先增加后减少,拉断伸长率逐渐降低,100%定伸应力和300%定伸应力呈升高趋势;高导电炭黑可大幅提高复合材料的导电性,复合材料的热刺激响应回复温度逐渐升高,热致形变回复率和热致回复速度均降低,热致形状记忆性能降低。复合材料具有良好的电致形状记忆性能,高导电炭黑的用量和外加电压对复合材料的电致形状记忆性能有重要影响,电致形变回复率和回复速度随外加电压或高导电炭黑用量的增加而增加。     

TPI形状记忆性能研究

研究硫黄用量对反式1,4-聚异戊二烯(TPI)硫化胶物理性能和热致形状记忆性能的影响以及TPI硫化胶的电致形状记忆性能。结果表明,随着硫黄用量的增大,TPI硫化胶化学交联密度和总交联密度增大,定伸应力和拉伸强度减小,拉断伸长率增大,热刺激响应回复温度降低,最终形变回复率增大,形变回复速率先增大后减小;TPI硫化胶具有良好的电致形状记忆性能,随着施加电压的增大,TPI硫化胶最终形变回复率增大,形变回复时间缩短。     

热致感应型形状记忆高分子材料与纤维

介绍了热致感应型形状记忆高分子材料的机理、制备方法及其应用,重点介绍了热致感应型形状 记忆纤维的混纺和后整理生产技术及国内外研究发展状况。指出今后应大力开发热致感应形状记忆纤维的 直接纺丝生产技术,提高纤维的形变回复力及尺寸稳定性,纤维的应用前景看好。     

电致形状记忆聚己内酯／炭黑复合导电高分子材料的研究

制备了具有电致形状记忆特性的聚己内酯/炭黑(PCL/CB)复合导电高分子材料,研究了其电致形状记忆特性。结果表明,以交联聚酯作为聚合物基体、导电炭黑作为导电填料的复合导电高分子材料具有良好的电致形状记忆特性。拉伸2倍的CB300-25试样在200V电压作用下的形变回复率可达100%,响应时间140s。炭黑质量含量为25%的试样与炭黑含量为20%的试样相比,其响应时间较短,形变回复率也较高。随着电压的提高,试样的响应时间缩短,形变回复率提高。     

形状记忆弹性体

形状记忆弹性体是具有特殊力学功能的功能高分子材料。由于其低温成型性、常温高硬性、高门尼粘度和高冲击强度、高热熔粘合性以及交联性等特性，越来越受到人们的青睐。形状记忆弹性体与其他材料相比具有以下几大特点：形变量大，形状记忆回复温度范围宽；质量轻，易包装运输；易加工，可制成复杂结构制件，能耗低；使用方便，价格便宜；耐化学品腐蚀，电绝缘性好，使用温度范围内绝热性好。     

偶氮苯液晶弹性体中不同的交联类型

偶氮苯液晶弹性体材料结合了偶氮化合物的光响应性、液晶的各向异性、聚合物的熵弹性的优点,偶氮苯液晶弹性体在光照(紫外光/可见光)的作用下可以利用分子间的协同作用将微观的光致异构化转变为宏观的形变,实现了将光能直接转化成机械能,而这一过程的实现离不开聚合物的交联作用。并且随着交联方式的不断改变,聚合物种类和性能也随之不断发展,比如聚合物的加工性能、光响应性等。本文主要根据交联方式的不断改变,阐述了偶氮苯液晶弹性体的发展。     

热塑性聚烯烃弹性体的单向形状记忆行为

以乙烯为单一原料采用串级催化体系制备了乙烯/1-己烯无规共聚物,具有从60℃到120℃宽的熔融峰,其储能模量在100 MPa 以下,研究此热塑性弹性体的形状记忆性质。采用DSC、DMA 等手段定量表征,结果表明,选择恰当的变形温度,共聚物的形状固定率和形状恢复率可达90%,实现较好的形状记忆性能。     

Semicrystalline Shape‐Memory Elastomers: Effects of Molecular Weight,Architecture, and Thermomechanical Path

Poly(caprolactone) networks are well‐studied shape‐memory polymers owing to their high fixity and recovery, their ability to store large amounts of elastic energy, and their tunable shape‐triggering temperature. To elucidate the influence of network structure on shape‐memory features, poly(caprolactone) networks are prepared by reacting different molecular weight diacrylate prepolymers with trifunctional (trimethylolpropane tris(3‐mercaptopropionate), 3T ) or tetrafunctional (pentaerythritol tetrakis(3‐mercaptopropionate), 4T ) crosslinkers. Networks from 4T crosslinkers generally exhibit higher gel fractions, more elastically active strands, and superior shape‐memory properties compared with networks from 3T . Melted elastomers exhibit stress–strain behavior well described by the neo‐Hookean model. How the state of crystallization during the cold‐drawing process has a large effect on the draw stress, the network's shape fixity, and its elastic storage capacity is shown. Finally, the working strain range of networks is evaluated. Cured elastomers prepared from prepolymers with different molecular weights can store and release large amounts of elastic energy (>2 MJ m⁻³), over different ranges of tensile strain.     

Dynamic Polyphosphazene Networks with Modulating Shape Memory and Self-Healing Capacity by Double Coordination Interactions

A modern class of self-healing polyphosphazene elastomers has been synthesized using coordination bonds for the first time. Two categories of carboxyl-modified polyphosphazene have been synthesized, and 16 cross-linked polymers have been fabricated by tuning the concentration of different metal ions, which also allows modifying the properties of the elastomer by adjusting the interactions. This design enables the polymer network to form a hierarchical and dynamic structure without introducing complex ligands. The polyphosphazene networks can be toughened and enhanced by the dynamic coordination structure. Due to the distinct design, the synthesized elastomers show unprecedented properties in halogen-free polyphosphazenes, including high tensile stress (1.82 MPa), high malleability (≈1100%), shape memory, self-healing, and thermal processing capacity.     

形状记忆聚氨酯的结构与性能研究

以2，4-甲苯二异氰酸酯、不同相对分子质量的聚己二酸丁二醇酯(PBAG)和1，4-丁二醇为原料合成了一系列聚酯型聚氨酯弹性体。发现由相对分子质量为3000和5000的PBAG所合成的聚氨酯弹性体具有良好的形状记忆功能。通过DSC、弯曲试验和力学性能测试研究了形状记忆聚氨酯的性能，发现软段高度结晶和硬段聚集形成硬段微区是使聚氨酯具有较好形状记忆功能的必要条件。     

Shape Memory Thermoplastic Polyamide Elastomer Based on PA1212

Shape memory polyamide elastomers have attracted large attention owing to a variety of favorable properties (e.g., designable chemical structure, good thermal stability, flexibility, and elasticity, et al). However, the polyamide elastomer reported recently still lack good mechanical property. In the present work, a new type of shape memory thermoplastic polyamide elastomer (TPAE), composed of long carbon chain PA1212 and polytetramethylene ether glycol (PTMEG), is synthesized through two-step melt polycondensation, which is named as poly(ether-b-amide) (PEBA). The chemical structure of PEBA is confirmed by FTIR results and it also shows excellent mechanical properties. PEBA, possessing two melting temperatures, stay in microphase separation among PTMEG soft domains and PA1212 hard domains that are amorphous and α crystal, respectively. Furthermore, PEBA can fix a temporary shape after the heated strip is twisted and cooled down and then recover to the original shape after secondary heating, which is attributed to the fixing force provided by PTMEG domains and entropy elasticity of physically cross-linked PA1212 domains, respectively. Besides, PEBA elastomer can be reshaped between ≈190 and ≈380 °C and it also has shape memory behavior. This new kind of TPAE proposes a new smart material for sensors and soft robotics.     

Supramolecular semicrystalline polyolefin elastomer blends with triple‐shape memory effects

Supramolecular polyolefin elastomer blends possessing triple‐shape memory effects were prepared by melt blending of two semicrystalline maleated elastomers (maleated ethylene‐propylene‐diene rubber (mEPDM) and maleated polyethylene‐octene elastomer (mPOE)) in the presence of a small amount of 3‐amino‐1,2,4‐triazole (ATA). The amino group of ATA reacted with the maleic anhydride groups of both elastomers during melt blending to form supramolecular hydrogen‐bonded networks. Dynamic mechanical analysis of the blends showed drops in the storage modulus at two different transition temperatures (T_trans) belonging to the crystalline melting temperatures of each phase as well as a plateau above these two T_trans. This is an essential property for triple‐shape memory behavior. Dual‐shape memory properties of the blends were determined using one‐step programming under three different temperature ranges. When an individual crystalline phase is used for the fixing process, the switching temperature (T_sw) relates to the melting temperature of a particular phase during the recovery process. However, if both crystalline phases are used simultaneously for the fixing process, then the T_sw relates to the higher melting temperature. Cyclic two‐step programming revealed that two different shapes can be fixed, one by EPDM crystallization and the other by POE crystallization, and both programmed shapes can be recovered upon heating above a specific T_sw. © 2016 Society of Chemical Industry     

Shape memory polyester-based nanomaterials: cutting-edge advancements

ABSTRACT

Shape memory polymers have gained immense importance across technical industries ranging from aerospace and electronics to biomedical fields. This article presents state-of-the-art overview of versatile shape memory polyesters and derived nanocomposites. Shape memory polyesters such as polylactic acid, polyhydroxyalkanoate, polycarbonate, and polyester blends have been identified. Shape memory polyesters have also been reinforced with nanoreinforcements including fullerene, graphene, carbon nanotube, and polyhedral oligomeric silsesquioxane (POSS). Consequently, different groups of stimuli-responsive polyester nanocomposites have been discussed such as polyester/graphene, polyester/carbon nanotube, polyester/fullerene, and polyester/POSS. Future development of shape memory polyesters may reveal superior electrical, mechanical, and thermal performance for technical applications.     

Synthesis and characterization of the properties of thermosensitive elastomers with thermoplastic and magnetic particles for application in soft robotics

In the currently rapidly developing field of soft robots, smart materials with controllable properties play the central role. Thermosensitive elastomers are soft, smart materials whose material properties can be controlled by changing their temperature. The aim of this work is to investigate the mechanical properties, to analyze the surface, the inner structure, and the heat transfer within the thermosensitive elastomer materials. This should provide a knowledge base for new combinations, such as a combination of thermosensitive and the well-known magneto sensitive elastomers, in order to realize new applications. Thermoplastic polycaprolactone particles were incorporated into a flexible polydimethylsiloxane matrix to produce thermosensitive elastomer samples. With a low melting point in the range of 58–60°C, polycaprolactone offers good application potential compared to other thermoplastic materials such as polymethamethylacrylate with a melting point above 160°C. Test samples of different material compositions and geometries were made to examine temperature-depending material properties. Two useful effects were identified: temperature-dependent change in stiffness and the shape memory effect. In certain examinations, carbonyl iron particles were also included to find out if the two particle systems are compatible with each other and can be combined in the polydimethylsiloxane matrix without disadvantages. Changes in shore hardness before and after the influence of temperature were investigated. Micro computed tomography images and scanning electron microscopy images of the respective samples were also obtained in order to detect the temperature influence on the material internally as well as on the surface of the thermosensitive elastomers in combination with carbonyl iron particles. In order to investigate the heat transfer within the samples, heating tests were carried out and the influence of different particle concentrations of the thermosensitive elastomers with and without carbonyl iron particles was determined. Further work will focus on comprehensive investigations of thermo-magneto-sensitive elastomers, as this will enable the functional integration in the material to be implemented with increased efficiency. By means of the different investigations, the authors see future applications for this class of materials in adaptive sensor and gripper elements in soft robotics.     

Vegetable oil/styrene thermoset copolymers with shape memory behavior and damping capacity

The mechanical and damping properties as well as the shape memory behavior of copolymers obtained by cationic copolymerization of tung oil with styrene with different stoichiometric ratios are presented and analyzed in this work. The glass transition temperatures are close to room temperature for all the copolymers, and generally increase with the content of styrene. A similar trend is observed for the modulus, which exhibits values from 4.89 MPa for the copolymer with 30 wt% styrene to 13.92 MPa for the copolymer with 70 wt% styrene. These hard elastomers present shape memory behavior with high recovery and fixity ratios, as well as high damping quality (damping factors 0.4 and 1.38 at 28.9 and 43.3 °C, for the tung oil homopolymer and the copolymer with 70 wt% styrene, respectively), opening possibilities for practical applications that require material response close to room temperature. Copyright © 2012 Society of Chemical Industry     

Carbonization and liquid-crystal (mesophase) development: Part 1. The significance of the mesophase during carbonization of coking coals

Recent concepts of the growth processes of liquid-crystal structures, also called mesophase systems, during the carbonization of pitch substances is extended to coal carbonization. A basic model is formulated to explain the coal and coal-blend carbonization processes leading to metallurgical coke. This model explains the differences observed by optical microscopy in the size and shape of anisotropic structures seen in cokes in terms of liquid-crystal growth processes. These processes are considered to be restricted by chemical heterogeneity within the plastic phase, or to be influenced by the presence of solid surfaces (inerts) within the carbonizing system.