Collaborative Research: Mechanics of Elastomers Tailored by Cation-Pi Interactions

Soft materials underpin important technologies such as adhesives, coatings, drug delivery, and energy storage. One key challenge with such materials is how they change when exposed to fluids, especially if these fluids contain dissolved salts (e.g., seawater, bodily fluids, or battery electrolytes). Soft materials will often dissolve, detach, or excessively swell in salty fluids, leading to their failure. This award supports research into a new class of soft materials designed for salty fluid environments. This research project will investigate the influence of molecular scale design on the mechanical properties of these materials. The resulting fundamental knowledge is intended to provide a foundation for adhesives or structures that strengthen in environments such as seawater; components that aggregate in response to specific salt species, enhancing desalination plants; and as salt driven muscle-like components for soft robotics. This award will also result in the interdisciplinary education of students in New York and Rhode Island in mechanical engineering and chemical sciences. the research will investigate a novel zipper-like molecular topology of soft polymeric materials decorated with tethered cationic and aromatic groups, termed ZIPers. These materials are simple to prepare on large scale and preliminary data shows that these ZIPers have a complex dependence of equilibrium structure and mechanical properties on the concentration and type of anion present in solution, features that can be dynamically adjusted by changes in ionic content. This research will utilize a combination of synthetic, experimental, and modeling approaches to provide insight into three aspects of their mechanical behavior: (1) the equilibrium structures and corresponding small strain oscillatory response of the ZIPer system as a function of monomer ratio, salt type, and salt concentration; (2) how the structure and crosslink dynamics determine the time dependent large deformation mechanical response of the ZIPer system; (3) potential of the ZIPer system to exhibit salt-driven shape-morphing. New mesoscale and continuum polymer modeling techniques will enable this work and also be standalone contributions to the mechanics of polymers field. This project will advance knowledge of the mechanics of dynamically bonded polymers and provide key insights into the properties of dynamic and responsive soft materials. 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.