Stretchable, Tough, Water-Retaining Hydrogels for Non-Traditional Applications

三维聚合物网络可以吸收大量的水并形成水凝胶。常见的例子包括果冻和吸水性尿布。水凝胶在生物医学领域的应用正处于激烈的发展之中，如组织工程中的支架和药物输送的载体。然而，大多数现有的水凝胶是弱的、脆的，并且不是非常可拉伸的。它们也会随着水分的蒸发而变干。这些问题严重限制了水凝胶的应用范围。该项目将开发可拉伸，坚韧和保水的水凝胶。具有增强的机械性能和环境稳定性的水凝胶将开辟新的应用。例子包括可拉伸的、透明的离子导体;防火毯;可膨胀的密封件;以及环境响应的致动器和传感器。由于许多原因，水凝胶的大规模使用具有吸引力。许多种类的聚合物可以形成水凝胶;这种多样性使得能够选择合适的聚合物来实现特定的功能。水凝胶主要由水组成，并且可以由天然存在的聚合物形成;许多水凝胶是廉价且环境友好的。水凝胶的力学行为也将作为一种工具，以弥合研究和教育之间的差距：从这个项目产生的新的见解将被纳入研究生课程;该项目将为高中生提供研究机会，并将利用iMechanica和YouTube等互联网网站，向全世界的读者介绍材料力学的最新发展。机会：性能增强的水凝胶可能会实现更广泛的应用，远远超出目前的设想。这一机会提出了关于开发可拉伸、坚韧、保水水凝胶的新的科学问题。该项目将利用非线性断裂力学以及聚合物科学的概念，研究控制水凝胶多种机械性能的机制，包括拉伸性，刚度，强度和韧性。该项目将研究增强水凝胶的机械性能和环境稳定性的方法，通过引入能量耗散机制来增强水凝胶，通过嵌入纤维来增强和加强水凝胶，通过修改弱键来实现变形后的愈合，以及通过添加吸湿成分来改变凝胶内部水的化学势。两大类的能量耗散机制将进行研究：可恢复的弱交联，如离子键和微晶，和水凝胶和嵌入的纤维之间的摩擦滑动的解离。

A three-dimensional polymer network may absorb a large quantity of water and form a hydrogel. Familiar examples include jello and superabsorbent diapers. Hydrogels are under intense development for biomedical applications such as scaffolds in tissue engineering and carriers for drug delivery. Most existing hydrogels, however, are weak, brittle, and not very stretchable. They also dry out as water evaporates. These issues have severely limited the scope of applications of hydrogels. This project will develop stretchable, tough, and water-retaining hydrogels. Hydrogels of enhanced mechanical properties and environmental stability will open new applications. Examples include stretchable, transparent, ionic conductors; fire-retarding blankets; swellable seals; and environmentally responsive actuators and sensors. Large-scale use of hydrogels is attractive for a number of reasons. Many kinds of polymers can form hydrogels; this diversity enables suitable polymers to be selected to achieve specific functions. Hydrogels consist mostly of water, and can be formed by naturally occurring polymers; many hydrogels are inexpensive and environmentally friendly. The mechanical behavior of hydrogels will also serve as a vehicle to bridge the gap between research and education: Fresh insights that arise from this project will be incorporated into graduate courses; the project will offer research opportunities to high-school students, and will use Internet sites such as iMechanica and YouTube to bring recent developments in the mechanics of materials to readers worldwide.Recent findings highlight a significant opportunity: hydrogels of enhanced properties may achieve much broader applications, well beyond those envisaged so far. This opportunity poses new scientific questions concerning the development of stretchable, tough, water-retaining hydrogels. The project will draw upon concepts of nonlinear fracture mechanics, as well as polymer science, to investigate the mechanisms that control multiple mechanical properties of hydrogels, including stretchability, stiffness, strength and toughness. The project will examine approaches that enhance the mechanical properties and environmental stability of hydrogels, by introducing energy dissipation mechanisms to toughen hydrogels, by embedding fibers to stiffen and strengthen hydrogels, by modifying weak bonds to enable healing after deformation, and by adding hygroscopic components to alter the chemical potential of water inside the gels. Energy-dissipation mechanisms of two broad types will be investigated: recoverable dissociation of weak crosslinks such as ionic bonds and crystallites, and frictional sliding between hydrogels and embedded fibers.