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.
