Crack Propagation in Self-Healing Polymer Gels with High Toughness

该项目的完成将导致具有特殊机械韧性的凝胶的开发，也具有自愈能力。这些类型的材料的应用领域非常多样化，从人工软骨到依赖于材料在重复加载条件下耗散大量能量的保护系统。合成坚韧聚合物凝胶的一般设计策略是基于最近对“双网络”凝胶的研究，该凝胶由一个相对高模量的初级网络和一个模量低得多的独立次级网络组成。在提出的工作中，二级网络是基于自组装的三嵌段共聚物凝胶，初级网络源于二级网络的额外离子交联，或者来自共连续的硅酸盐网络或二氧化硅纳米颗粒阵列的发展。这项工作的另一个成果是改进了非线性弹性断裂力学分析，从而对高变形固体中的裂纹扩展有了一个大致的了解。凝胶的自愈能力主要来源于在形成初级和次级网络时使用的非共价键。由于形成的共价键能够进行可逆的水解和缩合反应，在硅酸盐体系中还存在其他的愈合机制。这些杂化硅酸盐/有机凝胶的开发和理解将影响材料科学的广泛领域。为了实现这些目标，PI和co-PI提出了一个连贯的计划，包括综合初级和次级网络，并使用有限元方法来了解裂缝附近的应力场。还将连接到分析模型，这些模型更广泛地适用于对高变形材料的断裂韧性感兴趣的更广泛的科学和技术社区。许多天然材料具有高度优化的机械性能，并且尚未在合成材料中复制。其中一些天然材料最有趣的特性之一是它们的“自我修复”能力，使它们能够在被损坏后恢复其机械完整性。开发策略来实现这些天然材料所拥有的特性的平衡是这个项目的目标之一。重点是相对“柔软”的材料，类似于构成植物和动物软组织的材料。软骨是材料性能的理想组合的一个很好的例子。软骨通过在骨头表面之间提供低摩擦界面来润滑关节，即使骨头彼此之间受到非常大的压力。在这个项目中使用的设计策略将使合成材料能够获得这种特性的组合。这项工作是一项涉及机械建模、机械测试以及新材料合成和加工的合作努力。教育推广活动计划与芝加哥地区的当地博物馆合作，从芝加哥植物园和谢德水族馆开始。这些机构带来了在最广泛和最普遍的层面接触公众的专门知识。这些合作将使对自然环境有天然好奇心的人们能够在定性层面上理解拟议工作中应用的原则。

Completion of this project will result in the development of gels with exceptional mechanical toughness that also have a self-healing capability. Application areas for these types of materials are quite diverse and range from artificial cartilage to protection systems that rely on the ability of a material to dissipate large amounts of energy under repeated loading conditions. The general design strategy for the synthesis of tough polymer gels is based on recent work with 'double network' gels consisting of a relatively high-modulus primary network, and an independent secondary network with a much lower modulus. In the proposed work the secondary network is based on a self-assembling triblock copolymer gel, and the primary network originates either from additional ionic crosslinking of the secondary network, or from the development of a co-continuous silicate network or array of silica nanoparticles. An additional outcome of the work is the refinement of the nonlinear elastic fracture mechanics analysis needed to provide a general understanding of crack propagation in highly deformable solids. The self-healing capability of the gels originates primarily from the use of non-covalent bonds in the formation of the primary and secondary networks. Additional healing mechanisms are available in the silicate systems because of the formation of covalent bonds that are able to undergo reversible hydrolysis and condensation reactions. Development and understanding of these hybrid silicate/organic gels will impact a broad range of fields in materials science. In order to accomplish these goals the PI and co-PI propose a coherent plan that involves the synthesis of the primary and secondary networks and the use of finite element methods to understand the stress fields in the vicinity of a growing crack. Connections will also be made to analytic models that are more generally accessible to the broader scientific and technical communities interested in the fracture toughness of highly deformable materials.Non-Technical Summary Many naturally-occurring materials have mechanical properties that are highly optimized and have not yet been duplicated in synthetic materials. One of the most intriguing properties of some of these naturally-occurring materials is their 'self-healing' capability that enables them to recover their mechanical integrity after they have been damaged. Developing strategies for achieving the balance of properties possessed by these natural materials is one of the aims of this project. The focus is on relatively 'soft' materials, similar to those that make up the soft tissues of plants and animals. Cartilage is an excellent example of a desired combination of materials properties. Cartilage lubricates the joints by presenting a low friction interface between bone surfaces, even when the bones are pressed against one another with very high forces. The design strategy utilized in this project will enable this combination of properties to be obtained in a synthetic material. The work is a collaborative effort involving mechanical modeling, mechanical testing, and the synthesis and processing of new materials. Educational outreach activities are planned with local museums in the Chicago area, beginning with the Chicago Botanic Garden and Shedd Aquarium. These institutions bring expertise in reaching the public at the broadest and most general level. These collaborations will enable the principles being applied in the proposed work to be understood at a qualitative level by people with a natural curiosity about their natural environment.