Polymers combined with liquid metals are finding use in soft robotics, composites, and stretchable electronics. Here, we discuss the use of liquid metals to initiate polymerization as a route to form metal-containing polymers in a single step. Conventional free radical polymerization is normally initiated by initiator molecules that form free radicals via homolytic bond cleavage in response to heat, light, or redox reaction. On the other hand, nonconventional stimuli-induced polymerization (e.g. mechanical deformation, acidification) is emerging as an alternative way to polymerize monomers to high polymer. Here, we report liquid metal particle initiators that acts as a unique free radical source. First, sonication of gallium or gallium-based liquid metal in an aqueous solution of vinyl monomers can lead to free radical polymerization without such conventional initiators. Sonication ruptures the passivating oxide layers of the liquid metals thereby exposing the reactive bare gallium to the neighboring vinyl monomers. Spin trapping electron paramagnetic resonance reveals the generation of free radicals on the liquid metals. Time-of-flight secondary ion mass spectrometry measurements confirm direct polymer bonding to gallium, verifying the formation of surface-anchored polymer grafts. The high molecular weight polymer could form a physical gel as well as a chemically cross-linked hydrogel if crosslinker is added. Further, other types of stimuli (mechanical deformation and acidification) can initiate polymerization to form double network hydrogels with excellent mechanical properties. 

Radical Polymerization of Vinyl Monomers by Stimuli-Induced Liquid Metal Particle Initiators

The Virtual Technical Meeting of the Society of Engineering Science 2020 is the first fully virtual meeting of the SES community to envision and connect during the hiatus created by Covid-19, providing a platform for the exchange of ideas, and to showcase the latest research in the field of engineering science.

[Visit the Programme](https://drive.google.com/file/d/1BoCPBzrr1IQFANuzQI8a-paXCJoOcCkB/view?usp=sharing) | [Visit the Prerecorded Video/Poster List](https://drive.google.com/file/d/1XHLeEXJxEFjCSsNScuLDfMwy1X7oy7oJ/view?usp=sharing) | [View the Session Grid](https://drive.google.com/file/d/1VeDOC-Ev5m_ymYjXnjaXSZHR3_DARiLt/view?usp=sharing)