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，这些凝胶也具有自我修复能力。这些类型的材料的应用领域相当多样化，范围从人造软骨到依赖于材料在重复加载条件下消耗大量能量的保护系统。合成韧性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数的一级网络和一个模数低得多的独立二级网络组成。在所提出的工作中，二次网络是基于自组装的三嵌段共聚物凝胶，而一次网络要么来自二次网络的额外离子交联，要么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，以提供对高度变形固体中裂纹扩展的一般理解。凝胶的自我修复能力主要源于在形成初级和次级网络时使用非共价键。由于形成的共价键能够进行可逆水解和缩合反应，因此在硅酸盐体系中可以使用其他愈合机制。这些硅酸盐/有机杂化凝胶的开发和理解将对材料科学的广泛领域产生影响。为了实现这些目标，PI和共同PI提出了一个连贯的计划，其中包括综合初级和次级网络，并使用有限元方法来了解扩展裂纹附近的应力场。还将建立与分析模型的联系，这些模型对对高度变形材料的断裂韧性感兴趣的更广泛的科学和技术团体更容易获得。非技术概述许多自然产生的材料具有高度优化的机械性能，尚未在合成材料中复制。其中一些自然产生的材料最耐人寻味的特性之一是它们的“自我修复”能力，使它们能够在受损后恢复其机械完整性。制定策略以实现这些天然材料所具有的性能的平衡是该项目的目标之一。重点放在相对“柔软”的材料上，类似于构成动植物软组织的那些材料。软骨是理想的材料性能组合的一个很好的例子。软骨通过在骨骼表面之间呈现低摩擦界面来润滑关节，即使当骨骼以非常高的力相互挤压时也是如此。在这个项目中采用的设计策略将使这种性能组合能够在合成材料中获得。这项工作是一项合作努力，涉及机械建模、机械测试以及新材料的合成和加工。计划与芝加哥地区的当地博物馆一起开展教育推广活动，首先是芝加哥植物园和谢德水族馆。这些机构提供了在最广泛和最一般的层面上接触公众的专业知识。这些合作将使对自然环境具有天然好奇心的人能够在定性水平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.