金属离子诱导海藻酸盐凝胶多尺度微观结构及外场下的演变机制

Alginate is a new kind of marine biomaterials characterized with rich resource, renewability and biodegradability. Ease of gelation induced by crosslinking of metal ions brings alginate gels with broad applications and development prospect in biomedical and textile fields, etc. Nevertheless, due to the complex and variable structures, the processing and the controlled properties of alginate are challenges. In the present project, based on the ordered structure of junction zone, the multi-scale microstructures of alginate gels, including the stackings of inter-molecular chains and the distance between intra-molecular chains, are planned to be elucidated by the combination of small and wide angle X-ray scatterings. The variation law of multi-scale structures will be put forward by exploring the factors of the charge and the ion radius of metal ions, the ratio of G/M units and the molecular weight of alginate chain. Then the microstructure evolution under temperature and stretching fields will be further clarified by in situ method and the corresponding mechanism will be put forward. The evolution model of alginate gels with different initial crosslinking structures will be suggested. Finally, the relationship between external fields, the microstructures and ultimate performances will be established, which can realize the control of mechanical properties from molecular level. The above investigation can provide theoretical guidance and technical approach to the tailored preparation of high performance alginate gels (especially for film and fiber) and the development of other polysaccharide polymers crosslinked by metal ions.

海藻基高分子是一种来源丰富、可再生、可生物降解的新型海洋生物质材料，金属离子诱导凝胶特性使海藻酸盐在医疗、纺织等领域具有广阔的应用前景，但由于其微观结构复杂多变，导致加工和性能控制难度大。基于海藻酸盐凝胶交联区结构有序特点，本项目拟结合同步辐射小角/广角X射线衍射技术，阐明初始交联区多尺度微观结构，包括分子链间堆砌方式和分子链内间距，揭示多级结构随金属离子价态、有效离子半径、海藻酸分子链G/M比和分子量的变化规律；进一步原位研究温度场、拉伸场下的多尺度结构演变及机理，构建不同初始交联结构海藻酸盐凝胶的微观结构演变模型，并与其力学性能关联，从而达到从分子水平调控力学性能的目的。以上研究将为高性能海藻酸盐凝胶材料（特别是薄膜和纤维）的可控制备及其它金属离子交联多糖类高分子材料的开发提供理论依据和技术参考。

为从分子尺度调控海藻水凝胶的力学性能，本项目围绕金属离子基多尺度结构和成形过程中的结构演化展开研究。一方面，为了构筑稳固交联网络，采用杂化金属离子交联剂准确调控不同价态金属离子络合竞争力，成功构建“二维平面修饰三维网络”的交联结构单元，互补结构模型诱导强力学协同效应；进一步，提出原位自增强策略，利用同质增强相诱导的离子浓度差，离子自发扩散到基体-增强相界面，为应力传递提供牢固界面。另一方面，分别在水凝胶成形前、成形中和成型后调控分子链聚集。首先，采用原液自由水蒸发，海藻分子链自由靠近，降低的分子链间距促使体系氢键和离子键作用最大化重构，诱导水凝胶呈现“脆-韧”力学转变。与成形后失水诱导分子链聚集相比，该策略不受原始金属离子交联点限制，分子链可有效、有序靠近，物理相互作用位点激活程度更大。其次，利用海藻基双网络水凝胶成形过程，当第一网络预形成、第二海藻网络未交联时，创新采用溶剂诱导选择性相分离，既保证两分子链的互穿分布，同时诱导海藻分子链聚集形成局部微米级物理交联区，成功克服传统分子链聚集造成的水含量损失。以上研究结果为海藻及其它金属离子基多糖水凝胶的高性能化提供新思路。