【作者】 吕海宝；

【导师】 杜善义； 冷劲松；

【作者基本信息】 哈尔滨工业大学 ， 工程力学， 2010， 博士

【摘要】 形状记忆聚合物材料与形状记忆合金和形状记忆陶瓷相比较,具有许多优异的性能,如其最大形状恢复应变可达到100%以上、密度低、制备工艺简单、形状恢复温度可调节和生产制造成本低等。这些优势使形状记忆聚合物材料的应用前景特别广阔,目前它已经在航空航天、汽车、通讯和仿生医学等重要领域有了初步的应用。因此形状记忆聚合物材料的研究是目前智能材料与结构领域内的最热点之一。然而目前热敏性形状记忆聚合物的形状记忆效应驱动通常是通过直接加热的方式实现,这一驱动方式的驱动效率很低,并且在实施过程中也存在许多不方便。另一方面,由于热敏性形状记忆聚合物材料做为一种新兴的智能材料,其发展的历史相对较短,研究者对它的理论认识还不够全面,也不深刻,导致不能彻底分析并认识隐藏在材料宏观表象之后的微观机理。这些问题的存在,严重地限制了形状记忆聚合物的深入发展和应用。在这样的背景下,本论文提出并从实验方面实现混杂导电纤维填充型形状记忆聚合物纳米复合材料(固-固混合体系)和nanopaper复合型形状记忆聚合物纳米复合材料的电致驱动方式,发现并证实了溶剂和形状记忆聚合物混合体系(固-液混合体系)的溶液驱动方式,以及从理论方面推导并解释了上述形状记忆聚合物混合体系的热力学本构方程。本文第三章研究的内容是混杂导电纤维填充型形状记忆聚合物纳米复合材料和碳纳米纸复合型形状记忆聚合物纳米复合材料。采用电子扫描电镜、偏光显微镜、示差扫描量热仪、动态机械性能热分析仪、静态力学性能测试系统、四点探针电阻测量方法和Van der Pawu四点电阻测量方法系统地研究电致驱动形状记忆聚合物纳米复合材料的微观结构、玻璃化转变温度、热力学行为和电学属性。进而通过驱动实验,验证纳米复合材料的电致驱动形状记忆效应,并采用红外成像仪等设备记录了电致驱动形状记忆效应的形状恢复行为和温度场分布。然后根据实验结果分析并总结材料成分种类、含量以及其电学属性对电致驱动形状记忆聚合物纳米复合材料形状记忆效应的影响规律。在第四章的研究内容,通过引入塑性效应理论、高分子溶液理论、橡胶弹性理论和松弛理论等系统地提出并阐述“热敏性形状记忆聚合物的溶液驱动形状记忆效应”概念。进而采用苯乙烯基形状记忆聚合物作为试验对象,实验上证实热敏性苯乙烯基形状记忆聚合物的溶剂驱动形状记忆效应。期间发现并分别实现N, N-二甲基甲酰胺溶剂的化学极化效应驱动形状记忆效应和甲苯溶剂的物理溶胀增塑效应驱动形状记忆效应。采用热失重分析仪、示差扫描量热仪、动态机械性能热分析仪和红外光谱分析仪等设备研究并分析溶液驱动形状记忆聚合物的热力学行为和化学结构演变规律。总结溶液驱动形状记忆效应的作用机理是溶剂分子通过扩散作用渗透到聚合物材料中,被吸收的溶剂分子对聚合物网络结构产生增塑作用。增塑效应可以降低聚合物网络结构内部分子链段之间的相互作用力,提升聚合物分子链段的柔顺性和运动能力,进而与聚合物分子产生化学的或物理的相互作用,从而间接地降低聚合物材料的转变温度。当聚合物的转变温度降低至室温时,固定在形状记忆聚合物分子链段内部的弹性应变能得以释放,形状记忆效应因此触发。对于热敏性形状记忆聚合物,其形状记忆行为遵循松弛理论及其Eyring方程。从Eyring方程可知,形状记忆效应不仅受温度的影响,同时也受聚合物网络内聚能(或化学势)的影响,并且只决定于这两个影响因素。在第五章的研究内容中,通过改变形状记忆聚合物网络化学势的方式对热敏性形状记忆聚合物的形状记忆行为进行分析和研究。在聚合物与其固体或液体溶剂混合过程中,混合体系的熵函数和自由能函数等热力学参数会发生改变。由此联立混合过程中的热力学方程和松弛方程,可定量地获得聚合物网络的化学势在混合过程中受溶剂(或聚合物)在混合体系的体积百分含量、聚合物分子与溶剂分子的摩尔体积比和Flory-Huggins相互作用参数的影响规律。进而引入自由能方程,从理论方面推导并解释形状记忆聚合物混合体系,在不同受力状态下关于聚合物的化学势-应变和混合体系的应力-应变本构方程。更多还原

【Abstract】 Shape memory polymers (SMPs) offer a number of potential technical advantages that compared with its counterparts, namely shape memory alloys and shape memory ceramics, including high recoverable strain (more than 100%), low density, ease of processing and the ability to tailor the recovery temperature, programmable and controllable recovery behavior, and most important, low cost. These amazing advantages enable such materials to have a high innovation potential in application. The shape memory effect in SMPs can be utilized in many fields, from aerospace engineering, automobile, communications to biomedicine and many important fields. Although SMPs have found a few applications, they have not fully reached their technological potential. Largely due to that the actuation of shape recovery in thermal-responsive SMPs is normally driven by external heat. Another important issue is that there is a few of researches aimed at more complex shape memory behaviors resulting from lack of theoretical development and a short history of SMPs being as a novel smart materials. The mechanism behind these features can not be explored and discovered. As a result, the development and application of SMPs is seriously limited.On this motivation, the first aim of this project is to demonstrate the electro- activated shape memory effect of SMPs nanocomposites by blending hybrid filler and carbon nanopaper, respectively. In subsequence, solution-driven SMPs have been discovered and achieved on mixing with solvent. Finally, a thermodynamic constitutive equation is deduced and constructed to theoretically depict the shape memory behaviors of SMP composites or blends.The present work firstly studies the electro-activated shape memory behaviors of SMP nanocomposites by blending hybrid filler or carbon nanopaper in the third chapter of the dissertation. The morphology, glass transition temperature, thermomechanical and electrical properties of the SMP nanocomposites have been studied by the scanning electron microscope (SEM), optic microscope (OP), differential scanning calorimetry (DSC), dynamic mechanical thermal analysis (DMTA), static mechanical test frame with a series of digital controllers, four-point probe measurement method and Van der Pawn method, respectively. The shape recovery of SMP nanocomposite driven by electrically resistive Joule heating is therefore demonstrated and recorded. And an infrared video camera is used to monitor the temperature distribution and shape recovery simultaneously. Based on these experimental results, I analyze and discuss the correlations among the component type, fraction, electrical properties and shape memory behavior of SMP composite.In chapter 4, the plasticizing effect, theory of polymer solution, rubber elastic theory and relaxation theory are employed to systemically prove that the thermal-responsive SMP can have solution-driven shape memory effect. For the styrene-based SMP, the demonstration of chemo-responsive shape memory behavior has been conduct on mixing with N,N-dimethylformamide (DMF) solvent through chemically conjugated interaction. Alternatively, it also can be carried out on mixing with toluene solvent through physical swelling effect. After being immersed into solvent, the thermomechanical behaviors and change in chemical structure of SMP are performed on thermal gravimetric analysis (TGA), DSC, DMTA and Fourier transform infrared spectroscopy (FTIR). In summary, the mechanism behind these new features is the imbibed solvent molecules have a plasticizing effect on the polymer network in the form of diffusion. The plasticizing effect makes the interactive forces among tangled polymer molecules depressed, resulting in the flexility and motion capability of polymer molecules improved. The solvent molecules then have a chemical or physical interaction with the polymer molecules. All these interactions between solvent molecules and polymer molecules will inductively make the transition temperature of polymer reduced. When the switching temperature of SMP arrives at the room temperature or lower, the shape memory effect of SMP is therefore induced, resulting from the stored strain energy is released in polymer molecules. As a result, the SMP will relax to its original shape from the temporary (or deformed) shape.For the thermo-responsive SMP, the shape memory effect obeys with the relaxation theory and its Eyring equation. It indicates that the shape memory effect is only determined by two parameters, the temperature and internal cohesive energy (namely chemical potential). The present chapter 5 aims at the shape memory effect of SMP induced by inductively lowering the chemical potential instead of temperature heating. Based on the solution theory of polymer and thermodynamic of polymer solution, there will be changes in entropy and free-energy functions, as well as other related thermal parameters, when a polymer is on mixing with a solvent or solid. In combination of thermodynamic equation of polymer solution and Eyring equation, we can qualitative separate the effect of volume fraction of solvent molecule (or polymer molecule), molar volume ratio of polymer molecule to solvent molecule and Flory-Huggins solubility parameter on the chemical potential of SMP. Finally, the free-energy equations of polymer solution are employed to construct the polymer’s chemical potential-stretch and blend’s stress- strain constitutive equations, which can be used to theoretically describe the behaviors of SMP blends in respect to chemo-mechanical couplings.更多还原