碳纳米管的加入对聚偏氟乙烯/丙烯酸酯共混物形状记忆性能的影响

利用聚偏氟乙烯(PVDF)微小结晶的物理交联点作用,制备了形状记忆性能优异的聚偏氟乙烯/丙烯酸酯聚合物(PVDF/ACM)共混材料。为提高其形状回复应力,又将碳纳米管(CNT)引入该共混体系中,系统研究了PVDF/ACM/CNT三元体系纳米复合材料的制备、结构及性能。结果表明,碳纳米管在PVDF/ACM体系中分散均匀;在基本保持其形状记忆性能的前提下,加入质量分数为4%的CNT,材料在25℃时的储能模量由2000 MPa提高至3130 MPa。     

反应共混制备光触发形状记忆聚合物材料

基于羧基和环氧基的高反应活性,以甲基丙烯酸缩水甘油醚与乙烯共聚物(PE-GMA),甲基丙烯酸与乙烯共聚物(EAA)为原料,采用熔融共混的方法制备了交联聚烯烃材料。 采用差示扫描量热仪(DSC)和动态热机械分析仪(DMA)研究了其热力学性能及其形状记忆效应。 结果表明,材料具备很宽的熔融温度范围(40~110 ℃)和很宽的晶体尺寸分布。 利用材料晶体温度记忆的特性,成功地实现了材料的双重形状记忆效应,多重形状记忆效应和双向形状记忆效应。 利用石墨烯材料的光热效应,研究了材料的光触发形状记忆效应。 我们提出设计材料本体“温度梯度”的策略,实现了材料在无外力条件下的双向形状记忆效应。     

结晶行为对无定型/结晶聚合物共混体系形状记忆性能影响的研究进展

形状记忆聚合物因其具有质轻、低耗、形变量大、回复率高、形状可调、刺激方式多样等众多优点而受到广泛关注。相较于其它类型的形状记忆聚合物而言,共混型形状记忆聚合物的制备则更为简单方便。目前最常见的共混型形状记忆材料是无定型/结晶聚合物体系,其中结晶聚合物的结晶行为是影响整个体系形状记忆性能的关键。本文结合了该领域的研究现状,就结晶度、晶体尺寸以及晶体取向对共混体系形状记忆性能影响的研究进展进行了综述。     

具有可编程形状变形的热响应超分子水凝胶

形状记忆水凝胶(SMHs)作为一种智能软材料备受关注.目前复杂的制备工艺和缓慢单一的形状变形阻碍了其在智能柔性驱动器中的应用.本研究以丙烯酰胺(AAm)、α-甲基丙烯酸(MAA)、丙烯腈(AN)为原料,N,N,N′,N′-四甲基乙二胺(TEMED)为促进剂,利用氢键和偶极-偶极相互作用的协同效应,简单自由基聚合方法构建了热响应形状记忆超分子水凝胶(P(AMA)).研究结果表明,水凝胶具有高韧性(1.11±0.06 MJ/m³),高拉伸强度(0.22±0.02 MPa)和超过1000%的应变.可逆物理交联点的解离和重建赋予了水凝胶优异的热响应形状记忆行为:在10℃条件下5 min即可固定为临时形状,并在37℃条件下10 s内恢复原始形状.本研究构建的P(AMA)形状记忆超分子水凝胶具有易制备、低成本、坚韧和可编程形状变形等优点,在柔性驱动器、软机器人和电子皮肤等领域具有良好的应用前景.     

形状记忆磁性润滑表面的制备及对超顺磁液滴的滑动操控

将磁性粒子与形状记忆聚合物复合,通过设计渐变式构型构筑了梯度形状磁性材料,并与润滑涂层相结合,制备了一种磁性润滑表面.在磁性梯度的作用下,超顺磁液滴在表面上能够自发定向运动.借助于材料形状记忆效应对表面区域形态进行可逆调控,进一步展示了超顺磁液滴自发定向运动过程中的启停开关式控制,实现了将液滴定向自发运输与启停控制相结合.考察了磁性粒子含量对材料形状记忆性能的影响,以及区域形态调控尺寸与液滴滑动性能间的相互关系.机理分析进一步阐明磁场梯度提供的定向驱动力促使液滴定向自发输运,表面区域形态控制的可逆调控则可以在液滴运动过程中增加/消除黏滞阻力,基于两种因素的协同作用,可以实现对超顺磁液滴运动的智能操控.     

热适性形状记忆聚合物

动态共价交联聚合物的研究具有悠久的历史,其早期的工作着眼于如何解决应力松弛带来的聚合物材料力学性能降低的问题.20世纪90年代以来,利用动态共价键来主动设计聚合物网络的特殊可适性逐渐成为研究主流,其中包括自修复和重加工性.然而,受到动态共价键的种类、通用性及所实现功能的特异性等限制,对于动态共价交联聚合物网络的研究尚停留在基础阶段.本文以本课题组近期在动态共价交联形状记忆聚合物的研究为基础,结合其他相关工作,展示了通用共价键(酯键及氨酯键)的动态可逆性,并利用其设计了具有特殊性能和潜在商业化价值的形状记忆聚合物.在此基础上,我们提出分子结构设计及宏观性能均不同于传统热塑性和热固性形状记忆聚合物的第3类形状记忆聚合物,即热适性形状记忆聚合物.     

苯乙烯基形状记忆聚合物热力学行为的有限元分析

对苯乙烯基形状记忆聚合物进行了拉伸实验研究,测定了该材料在25℃、30℃、40℃和50℃时的弹性模量和屈服极限.根据实验结果,建立了苯乙烯基形状记忆聚合物的材料参数方程,描述了苯乙烯基形状记忆聚合物在玻璃体转化过程中,材料参数和温度的关系.在假设形状记忆聚合物为各向同性材料的基础上,将Tobushi等建立的热力学本构方程从一维扩展到三维.基于有限元分析软件ABAQUS的二次开发功能,针对上述本构方程和材料参数方程,编写了可供ABAQUS调用的UMAT函数,并对苯乙烯基形状记忆聚合物实现形状记忆效应的高温变形、应力冻结和形状恢复等热力学过程,进行了有限元数值模拟分析.     

基于可逆共价化学的交联聚合物加工成型研究——聚合物工程发展的新挑战

可逆共价聚合物能够通过外界刺激(包括加热、光和pH)触发可逆反应,从而实现聚合物拓扑结构的重组,同时在撤销刺激后又可以像不可逆共价聚合物一样保持结构稳定性.近年来,越来越多的研究者致力于利用该特性来解决交联聚合物加工成型的难题,这不仅打破了传统热塑性聚合物和热固性聚合物的严格界限,而且带来了新的材料研发方法和功能,使得聚合物制品种类更加多样化,其生命周期也相应得以延长.孕育着传统聚合物工程领域的新突破,具有重要价值.为及时反映这一态势,本文总结了可逆共价化学的基本原理,阐述了可逆共价聚合物的流变特性,并且综述了由此衍生的含可逆共价键交联聚合物各类成型加工技术原型和应用,如力学性能调控、塑性变形、焊接、纳米填料的分散与增强效应、模压成型与固相回收、注射成型、挤出成型、3D打印、碳纤维复合材料的可控降解与再生等,在此基础上,进一步分析了该新兴领域的挑战和发展趋势.     

热可逆交联环氧树脂的动态结构与性能研究

通过双马来酰亚胺与侧链带有呋喃官能团线性环氧树脂间的Diels-Alder反应,制备了热可逆交联的环氧树脂(DAERs),通过热分析、固体核磁共振技术和力学性能测试详细研究了该热可逆交联聚合物中的热可逆转变过程、动态化学键演化以及交联度对力学性能的影响.示差扫描量热法(DSC)和动态热机械分析(DMA)等热分析结果表明,可逆共价键的化学交联作用提高了材料的玻璃化转变温度,随着交联度的增大,热可逆共价键断裂及玻璃化转变协同作用导致材料软化温度显著提高,进而提高了材料的耐热性.通过变温13C固体NMR实验原位监测DA/retro-DA反应过程,发现DAERs中通过DA反应形成的交联网络结构可以在高温解交联而生成呋喃与马来酰亚胺小分子化合物,而低温时呋喃与马来酰亚胺化合物又再次反应得到DA加成结构,进而从分子水平上为材料的热可逆交联特性提供了关键的实验证据.而原样品和溶液法再加工样品的拉伸实验结果表明,可逆交联DA反应不但使样品具有较高的力学强度,而且使交联聚合物具有了再加工的能力.     

形状记忆聚偏氟乙烯/丙烯酸酯/碳纳米管纳米复合材料的导电及导热性能

利用聚偏氟乙烯(PVDF)微小结晶的物理交联点作用,制备了形状记忆性能优异的聚偏氟乙烯/丙烯酸酯聚合物(PVDF/ACM)共混材料,为提高其导电及导热性能,于其中引入了碳纳米管(CNT),系统研究了PVDF/ACM/CNT三元体系纳米复合材料的导热及导电性能。结果表明,碳纳米管在PVDF/ACM体系中分散均匀;在基本保持其形状记忆性能的前提下,碳纳米管的加入使材料导热性能及导电性能有较大程度的提高:质量分数为4%的CNT使材料25℃的电阻值降低至5000Ω/square,导热系数提高至0.157 W/(m·K)。     

Reversible shape-shifting in polymeric materials

In recent years, significant progress has been made in polymeric materials, which alter shape upon external stimuli, suggesting potential applications in robotics, biomedical engineering, and optical devices. These stimuli-responsive materials may be categorized into two classes: (i) shape-changing materials in which a specific type of shape-shifting is encoded in the original material structure and (ii) shape-memory materials, which do not possess any predetermined shape-shifting as prepared, yet allow programming of complex shape transformations on demand. While shape alterations in shape-changing materials are intrinsically reversible, shape memory is usually a one-way transformation from a metastable (programmed) to an equilibrium (original) state. Recently, different principles for both one-way reversible and two-way reversible shape memory have been developed. These offer a powerful combination of reversibility and programmability, which significantly expands the range of potential applications. The goal of this review is to highlight recent developments in reversible shape-shifting by introducing novel mechanisms, materials, and applications. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1365–1380     

A Facile Approach Toward Scalable Fabrication of Reversible Shape‐Memory Polymers with Bonded Elastomer Microphases as Internal Stress Provider

The present communication reports a novel strategy to fabricate reversible shape‐memory polymer that operates without the aid of external force on the basis of a two‐phase structure design. The proof‐of‐concept material, crosslinked styrene‐butadiene‐styrene block copolymer (SBS, dispersed phase)/polycaprolactone‐based polyurethane (PU, continuous phase) blend, possesses a closely connected microphase separation structure. That is, SBS phases are chemically bonded to crosslinked PU by means of a single crosslinking agent and two‐step crosslinking process for increasing integrity of the system. Miscibility between components in the blend is no longer critical by taking advantage of the reactive blending technique. It is found that a suitable programming leads to compressed SBS, which serves as internal expansion stress provider as a result. The desired two‐way shape‐memory effect is realized by the joint action of the temperature‐induced reversible opposite directional deformabilities of the crystalline phase of PU and compressed SBS, accompanying melting and orientated recrystallization of the former. Owing to the broadness of material selection and manufacturing convenience, the proposed approach opens an avenue toward mass production and application of the smart polymer.     

Shape memory behaviors of crosslinked copolymers containing stearyl acrylate

Shape memory polymers were prepared by copolymerizing stearyl acrylate and methyl acrylate. The principle of this shape memory effect is based on reversible order-disorder transition of crystalline aggregates of stearyl moieties. A specific feature of this type of shape memory copolymer is that the transition temperature at which the polymer abruptly becomes soft and deforms can be controlled by changing the monomer composition, which enables one to adjust the shape memory effect at a desired temperature. Mechanism and process of the shape memory behaviors were discussed.     

Facile fabrication of thermoplastic ternary copolymerized polyamide and maleated polyethylene shape memory blends

Novel thermoplastic shape memory blends of ternary copolymerized polyamide (PAM) and maleated polyethylene (PE-g-MAH) were prepared by a simple melt-blending method, which might provide a new way for the industrial production of thermoplastic shape memory materials. The new chemical bonds were generated between PAM and PE-g-MAH, which was essential for enhancement of properties. The mechanical, thermal and shape memory properties of the blends were investigated in detail. It was found that the microstructure and proportion of different constituents was vital for the shape memory properties of the blends. In PAM/PE-g-MAH blends, a crystalline region of PAM acted as a fixed domain, and the crystalline region in PE-g-MAH acted as a reversible domain. The synergistic effect of the fixed and reversible domains determined the shape memory behavior of the blends. When the blend ratio of PAM/PE-g-MAH was 30/70, the composites exhibited the best shape memory properties, with a shape fixity ratio of 95.5% and a shape recovery ratio of 79.8%.     

Quadruple‐shape‐memory effect of TPI/LDPE/HDPE composites

Shape‐memory polymers are important smart materials with potential applications in smart textiles, medical devices, and sensors. We prepared trans‐1,4‐polyisoprene, low‐density polyethylene (LDPE), and high‐density polyethylene (HDPE) shape‐memory composites using a simple mechanical blend method. The mechanical, thermal, and shape‐memory properties of the composites were studied. Our results showed that the shape‐memory composites could memorize 3 temporary shapes, as revealed by the presence of broad melting transition peaks in the differential scanning calorimetry curves. In the trans‐1,4‐polyisoprene/LDPE/HDPE composites, the cross‐linked network and the crystallization of the LDPE and HDPE portions can serve as fixed domains, and all crystallizations can act as reversible domains. We proposed a schematic diagram to explain the vital role of the cross‐linked network and the crystallization in the shape‐memory process.     

Novel Shape-Memory Polymer with Two Transition Temperature Based on Two Different Memory Mechanism

As an important kind of intelligent materials, shape-memory materials have been received increasing attention on account of their interesting properties and potential applications in recent years. Particularly, the rise of shape-memory polymers by far surpasses well-known metallic shape-memory alloys in their shape-memory properties. The advantages of polymers compared to other materials are their easier availability and their wide range of mechanical and physical properties. The polymers designed to exhibit a shape-memory effect require two components on the molecular level: crosslinks to determine the permanent shape and switching segments with Ttrans to fix the temporary shape. Up to now almost all papers on shape-memory polymers introduce switching segments with the covalent linking method. On the other hand, only several cases concern non-covalent interaction. However, the research works mentioned above is based on a single Ttrans (i.e., Tm or Tg).Following our previous work, here, we first report a novel kind of polymer consisted of PMMA-PEG semi-interpenetrating polymer networks (semi-IPN), which exhibiting independently two shape memory effects based on Tm and Tg, respectively. This result can also extend the shape memory polymer categories from one Ttrans to two Ttrans, and the combination of Tm and Tg give rise to an extremely excellent shape-memory effect.Two different shape memory behaviors of this material based on two transition temperatures were evaluated by bending test as follows: a straight strip of the specimen was folded at a temperature above Ttrans and kept in this shape. The so-deformed sample was cooled down to a temperature Tlow＜ Ttrans and the deforming stress were released. When the sample was heated up to the measuring temperature Thigh ＞ Ttrans, it recovered its initial shape. The deformation angle θ f varied as a function of time and the ratio of the recovery was defined as θ f /180. The PMMA-PEG polymer behaved as a hard plastic at room temperature and did not deform at all under a given stress. However, if upon cooling; even after unloading, it did not recover the initial shape. When the polymer was ratio reach 90%. This observation illustrates that the shape memory phenomenon with 90%recovery ratio was found to be archived by changing the operation temperature below and above of Tm of crystalline PEG, which is based on a reversible order-disorder transition of crystalline aggregates. Similarly, the investigation on the shape memory transitin at Tg that when the sample (above Tg of the semi-IPN), the polymer showed second shape memory behavior, and quickly recovered to initial shape in 45s with shape recovery ratio more than 99%.     

Synthesis and characterisation of biodegradable liquid crystal elastomer with the property of shape recovery

Novel shape recovery biodegradable liquid crystal (LC) elastomer is reported here for the first time. The method of synthesis of the shape memory biodegradable LC elastomer has been explored. During the reaction, the LC molecules are added to form LC polymers, and then cross-linking agent is added to form a cross-linked LC elastomer. The LC elastomer in this work is hydrophilic. In vitro degradation of the LC elastomer films in a buffer of pH 7.4 at 37°C shows that the LC elastomer has good degradability. The biodegradable LC elastomer exhibits liquid crystalline behaviour and has shape memory ability. Its shape memory and actuating properties also have been studied. The reversible transition from liquid crystalline phase to isotropic phase is utilised as the switching mechanism for these stimuli-responsive materials. When reheating the LC elastomer to 120°C, the shape will recover.     

液晶弹性体刺激形变研究

开发可以通过外部刺激产生机械形变的人工致动材料是一个近年来的研究热点。其中,液晶弹性体因结合了聚合物网络的橡胶弹性和液晶的有序性而具有独特的性质,在热、光、电等的外界刺激下可以产生可逆的形状记忆效应。本文综述了液晶弹性体响应多种外界刺激产生各种形变的行为,主要介绍了有关热致形变液晶弹性体、电致形变液晶弹性体、化学刺激导致形变的液晶弹性体及光致形变液晶弹性体的研究进展,阐述了各类液晶弹性体产生形变的机理包括热致、电致和光致相转变,讨论了影响其响应性能的主要因素,并展望了这一领域的发展前景。     

Shape memory properties of polyethylene/ethylene vinyl acetate /carbon nanotube composites

The safe operation of electrical equipment relies on advanced polymer insulation to contain electrical pathways. Polymer sheath materials should be mechanically robust and chemically stable in order to protect the internal metal wiring from environmental attack. Polyethylene (PE) and ethylene vinyl acetate (EVA) have often been used as electrical cable jacket materials for electrical power industry. Partially crosslinked PE is able to shrink and wrap tightly around the metal wires upon stimulated by external heat, exhibiting shape memory behaviour. In this work, multiwalled carbon nanotubes (MWCNTs) were introduced to partially crosslinked linear medium density polyethylene (LMDPE) and EVA blend in order to enhance the shape memory performance at lower temperature by promoting the thermal transfer and antistatic properties of the polymer nanocomposite. The morphologies of the partially crosslinked and non-crosslinked composites are analysed. The MWCNTs preferentially resided in the EVA phase while the peroxide crosslinking process drastically altered the morphology and electrical properties. The addition of 3 wt% of MWCNTs resulted in a percolation transition and enhanced the alternating current (AC) conductivity by 10 orders of magnitude for non-crosslinked LMDPE/EVA and by 3 orders of magnitude for crosslinked LMDPE/EVA composites. LMDPE/EVA (80/20) containing 3 wt% MWCNTs possessed excellent shape recovery of 100% and shape fixing of 82%. The addition of MWCNTs can not only promote the shape memory efficiency of the polymer sheath material, but also introduce antistatic properties to avoid electrical shocking or sparking.