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

这项拨款将使用压痕技术来探测水凝胶在水下条件下大范围长度和时间尺度的粘附特性和机制。水凝胶是一种由聚合物链网络组成的软凝胶，具有很高的含水量，是重要的工程材料和生活部件。在天然环境和工程环境中，水凝胶通常与其他材料或生物成分相结合。定量地了解水凝胶的粘附特性和粘附机理对材料的设计和制造控制具有重要意义。凝胶的粘附是一个与许多分子过程相关的时变过程。在不同的长度尺度上，粘附机理往往不同。该项目将结合一种新的基于物理的理论和多尺度力学表征技术来揭示水凝胶的粘附机制。从技术的角度来看，这项研究的成功将导致一种强大的、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特性，并为定量材料设计和制造提供一般指导。该研究还与一项长期教育计划同时进行，该计划旨在培养软材料工程跨学科领域的下一代科学家和工程师，并推广在该研究领域获得的科学和技术。本研究的具体目标是清晰地了解聚合物网络的分子结构和化学性质与水凝胶的宏观粘附性能的关系，这将有助于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，该理论结合了体的非线性孔隙弹性和压头与水凝胶之间相互作用的随机内聚区模型；(2)开发一种压痕方法，该方法提供了足够的信息来解耦体和表面行为，并允许从理论中提取固有的界面属性；(3)探索水凝胶随时间和长度变化的粘附微观机制。将回答以下基本问题：(1)黏附滞后与水凝胶的微观结构、键的形成和断裂、液-聚合物相互作用和流体流动之间的关系；(2)是什么决定了黏附机制从断键到断裂的过渡长度，以及它如何受到水凝胶的非线性变形和网络拓扑结构的影响？(3)温敏凝胶发生体积相变时，其表面性质变化的决定机制是什么？该项目将推动当前粘附科学的前沿，并推动现有的软材料和生物组织的粘附知识。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.