This Faculty Early Career Development (CAREER) project will develop a new experimental technique to characterize the nonlinear thermodynamic and kinetic properties of gels. Defying the classical definitions of solid and fluid, gels are both solid-like and fluid-like. They are both ubiquitous components of natural organisms and important engineering materials. Despite their wide applications, the design of these materials at this stage remains mostly trial-and-error due to a lack of fundamental understanding of the complex thermodynamic and kinetic behaviors of gels. The success of this work will lead to a robust and high throughput technique capable of measuring the thermodynamic and kinetic properties of soft gels under wide range of conditions and provide a standard toolbox for engineers to realize quantitative designs based on these materials. The PI will also expand a Soft Squishy Lab to combine visual, tactile and hands-on modules to connect human perception of macroscopic properties to the underlying microstructures of soft materials at appropriate levels for K-12 students.
Gels are composed of crosslinked polymer network and solvent molecules. The crosslinks prevent the long polymers from dissolving in the solvent; rather the gel swells and shrinks as the small molecules migrate in and out. The solvent uptake is a two-way street: as the solvent diffuses into the network, the network deforms, leading to size and shape changes, while the deformation of the network also affects the rate and amount of solvent diffusing into or out of the network. Both the concepts and the behaviors of gels are sufficiently complex such that ample room exists for additional work to connect principles of mechanics, thermodynamics, and kinetics to experiments. The proposed study will develop a technique based on an indentation method for characterizing the nonlinear thermodynamic and kinetic properties of gels. The new technique will allow for systematic characterization of various types of stimuli-responsive gels under different environmental conditions. Based on a complete set of data from the systematic measurements, an in-depth understanding of the structure-property relations of gels can be achieved. Consequently, a physics-based constitutive model will be built.
