溶液环境中水凝胶的本构关系及细观机理研究

With the properties of softness, nontoxic and good biocompatibility, hydrogel is an excellent material in various fields including biology, medical treatment and soft robot. Inside organisms, hydrogels are generally infiltrated in the solution, and expel or absorb water under changing loads, which makes the mechanical behaviors significantly different from that in the air. The meso-structure and the interaction with water of the polymer network of the hydrogel are the key factors that determine these differences, but there is currently no effective meso-model to quantitatively analyze the influence of these factors. Aiming at studying the meso-mechanism of the hydrogel mechanical behavior in solution environment, this project plans to develop the meso-model and perform macro experiments, and mainly includes: (1) research and establish a hydrogel model containing the interaction of polymer network structure and water; (2) using the hydrogel meso-model, to study the changes of the polymer network and the water expulsion or absorption behavior under external loads, and to explore the meso-mechanism of the mechanical behavior of hydrogel; (3) study and establish the constitutive relation of hydrogels containing polymer meso-parameters in solution environment. The research project will not only conducive to understand the meso-mechanism of hydrogel macro behavior such as nonlinearity, compressive water expulsion and asymmetric deformation of tension and compression, but also provides theoretical basis for the design of hydrogel materials, and promotes the development of hydrogels, so it has important scientific and engineering significance.

水凝胶具有质软、无毒、生物相容性好等特性，在生物、医疗、软体机器人等领域具有优异的发展前景。在生物内部，水凝胶一般浸润在溶液中，在变化荷载作用下会出现失水或吸水现象，这使其力学行为与在空气中有显著不同。水凝胶聚合物网络的细观结构及与水的相互作用是决定这些不同的关键因素，但目前尚缺乏有效的细观模型以定量性地分析这些因素的影响。本项目拟针对溶液环境中水凝胶力学行为的细观机理，开展细观模型研究和宏观实验，主要包括：（1）研究和建立包含聚合物网络结构与水共同作用的水凝胶模型；（2）应用水凝胶细观模型，研究在外部荷载下聚合物网络的变化与失水或吸水行为，探索凝胶力学行为的细观机理；（3）研究和建立在溶液环境中包含聚合物细观参数的水凝胶本构关系。本项目的研究不仅有助于了解凝胶宏观力学非线性、压缩失水、拉压不对称等行为的细观机理，还能为凝胶材料的设计提供理论依据，促进其应用发展，具有重要的科学与工程意义。

本项目在实施期间开展顺利，基本完成了既定目标，在水凝胶材料的力学性能测试和模型研究方面取得了不少成果，并以此为基础，初步延伸展开了针对同样为高含水软材料的猪脑组织的研究。具体地，在实验测试方面，通过使用数字图像法获得了高含水率PVA水凝胶在溶液环境中的体积变化曲线，并发现了该材料具有形状效应；通过测试并显微观测被浸泡过不同浓度NaOH溶液的PVA水凝胶发现，NaOH溶液可改变PVA水凝胶纤维网络的细观结构，从而使水凝胶的宏观力学性能得到增强；使用双子弹电磁驱动SHPB系统测试了软材料（硅胶、水凝胶）在溶液环境中的动态力学性能，并提出了一套修正溶液影响的方法；使用与水凝胶实验相似的技术，初步测试了猪脑组织在不同环境中的准静态和动态力学性能。在模型研究方面，根据实验结果提出了包含体积变化和环境因素的水凝胶本构方程组；利用有限元纤维网络模型提出了评估PVA水凝胶聚合物交联密度的方法，并分析了在多轴加载条件下水凝胶试件中的水和聚合物纤维分别对外荷载的贡献。