Probing the Adhesion Mechanisms of Hydrogels in Underwater Conditions through Multi-Length and Multi-Time Scale Indentations

这项资助将使用压痕技术，在水下条件下探索水凝胶在各种长度和时间范围内的粘合特性和机理。水凝胶是一种由高含水率的高分子链网络组成的软凝胶，既是重要的工程材料，也是生命的组成部分。在自然和工程环境中，水凝胶经常与其他材料或生物成分相互作用。量化水凝胶的粘接性能，了解水凝胶的粘接机理，对于材料设计和生产控制具有重要意义。凝胶的黏附是一个时间相关的过程，涉及到许多分子过程。在不同的长度尺度上，粘着机理往往是不同的。这个获奖项目将结合一种新的基于物理的理论和一种多尺度的机械表征技术来解开水凝胶的粘合机制。从技术角度来看，这项研究的成功将带来一种稳健和高通量的技术，能够在广泛的条件下测量软水凝胶的内在相互作用性质，并为定量材料设计和制造提供一般指导。这项研究还与一项长期教育计划同步进行，以培养未来一代软材料工程跨学科领域的科学家和工程师，并普及该研究领域的科学技术。这项研究的具体目标是建立清晰的视野，了解聚合物网络的分子结构和化学与水凝胶宏观粘合性能的关系，这将促进未来的材料和制造设计。该项目的目标包括：(1)建立一个基于物理的理论，它结合了块体的非线性孔弹性和压头与水凝胶之间相互作用的随机内聚区模型；(2)发展一种压痕方法，提供足够的信息来分离块体和表面行为，并允许从理论中提取固有的界面性质；(3)探索水凝胶依赖于时间和长度的粘附性的微观机制。将回答以下基本问题：(1)水凝胶中的粘合滞后与微观结构、键的形成和断裂、液-聚合物相互作用和流体流动有何关系？(2)是什么决定了粘合机制从键断裂到断裂的转变长度，它是如何受到水凝胶的非线性变形和网络拓扑的影响的？(3)当温度敏感凝胶经历体积相变时，决定其表面性质变化的机制是什么？该项目将推动粘合科学最新技术的发展，促进软材料和生物组织粘合的现有知识。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This grant will use indentation technique to probe the adhesion properties and mechanisms of hydrogels across a wide range of length and time scales in underwater conditions. Hydrogels, a soft gel consisting of a network of polymer chains with a very high water content, are both important engineering materials and living components. In both native and engineering settings, hydrogels often interface with other materials or biological components. Quantifying the adhesion properties and understanding the adhesion mechanisms of hydrogels are important for material design and manufacturing control. Adhesion of gels is a time-dependent process related to many molecular processes. The mechanism of adhesion is often different in different length scales. This awarded project will combine a new physics-based theory and a multiscale mechanical characterization technique to unravel the adhesion mechanisms of hydrogels. From the technology standpoint, the success of this research will lead to a robust and high throughput technique capable of measuring the intrinsic interaction properties of soft hydrogels under a wide range of conditions and provide general guidelines for quantitative material design and manufacturing. The research is also in parallel with a long-term educational plan to prepare future generations of scientists and engineers in the interdisciplinary area of soft materials engineering, and to popularize science and technology gained in this field of study.The specific goal of this research is to build clear vision into the molecular structures and chemistries of the polymer network in relation to the macroscopic adhesion properties of hydrogels, which will facilitate future material and manufacturing design. The objectives of this project include (1) establishing a physics-based theory that combines the nonlinear poroelasticity for the bulk and a stochastic cohesive zone model for the interactions between the indenter and the hydrogels; (2) developing an indentation method that provides enough information to decouple the bulk and surface behaviors and allows for extracting intrinsic interface properties from the theory; (3) exploring the micromechanisms of the time- and length-dependent adhesion of hydrogels. The following fundamental questions will be answered: (1) how is the adhesion hysteresis related to the microstructure, bond formation and breakage, liquid-polymer interaction and fluid flow in hydrogels? (2) what determines the transition length of adhesion mechanism from bond breaking to fracture and how is it influenced by the nonlinear deformation and network topology of the hydrogels? (3) what is the mechanism that determines the surface property change of a temperature-sensitive gel when it undergoes volume phase transition? This project will push the boundary of current state of art in adhesion science and advance the existing knowledge on adhesion of soft materials and biological tissues in general.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.