About 50% of thermoplastic elastomers, colloquially known as (synthetic) rubbers, are created from ABA triblock copolymers that self-assemble into hard spherical domains of A embedded in a soft matrix of B. Unfortunately, thermodynamics place an upper bound on the mechanical performance of these materials, limiting the overall stiffness, strength, and toughness that can be achieved while still maintaining elasticity. Inspired by simulations from our collaborators, we are investigating branched molecular architectures (miktoarm star polymers) that are predicted to overcome these traditional constraints and produce unique material properties. Since the requisite A(BA’)n architecture is traditionally difficult to construct, we have devised a new, simpler synthetic route that provides facile access to a range of different A and B block chemistries. Current studies continue to experimentally and theoretically probe the ramifications of this new molecular design.
Traditional elastomers can only be rendered moderately soft (in the absence of solvent) due to the linear chains that connect crosslink points. In collaboration with Prof. Michael Chabinyc (UC Santa Barbara), our group is leveraging a relatively new type of “bottlebrush” polymer architecture to overcome this limitation and produce “super-soft” elastomers that are 10–100 times softer than commercial products. We are particularly interested in developing device friendly materials and processing strategies that permit the facile integration of bottlebrush elastomers into pressure sensors and actuators for soft robotics applications. Initial efforts have culminated in a new photo-crosslinking approach that can be used to easily crosslink any type of bottlebrush polymer in a matter of minutes. Using this technology to fashion parallel plate capacitive pressure sensors results in a massive performance boost due to the use of new bottlebrush materials with tailored structure and rheology.
Traditional crosslinked polymers are used in a variety of popular applications ranging from plastics in the bulk to solvated hydrogels for biomedicine. However, the same covalent bonds that imbue these materials with some beneficial attributes — like chemical resistance and strength — generally prevent other desirable properties, e.g., recyclability to mitigate the plastic waste catastrophe and reconfigurability for tissue scaffolding. To capture the best of both worlds, we are studying a class of materials that incorporate dynamic covalent bonds, which maintain the properties of typical crosslinked polymers during use but undergo on-demand exchange reactions in response to an external stimulus. We are particularly excited by the prospect of creating designer environments that promote three-dimension cell growth in collaboration with Prof. Skirmantas Janusonis (UC Santa Barbara).