(732i) Invited Talk: Using Light to Locally Tune the Properties of Polymers

This talk will describe two related projects that utilize generic light sources to induce localized changes to the physical and mechanical properties of polymers in a strategic manner.  The first project utilizes photopolymerization to change the properties of the walls of microfluidic channels.  Poly(dimethylsiloxane) is one of the most popular materials for microfluidics, but swells in the presence of most organic solvents and is therefore limited to handling aqueous fluids.  We show that it is possible to diffuse photoinitiator into the walls of the channel to localize photopolymerization that results in a thin shell that is impervious to organic solvents due to crosslinking.  The remainder of the polymer that composes the microchannel retains the desirable properties of siloxanes.   The second project utilizes uniform light from an IR heat lamp to induce self-folding of polymer sheets.   Regions of black ink patterned on sheets of pre-strained polymer absorb the light and heat up due to the photothermal effect.  The heat causes the polymer beneath the ink to relax and therefore shrink, which can induce self-folding.  Self-folding is similar to origami but is done without direct human intervention.  The appeal of our approach is that it utilizes two dimensional patterns to create a variety of complex three dimensional objects.  In essence, it allows shape memory polymers to be programmed using a variety of two dimensional patterning techniques and triggered using only light.  The talk will discuss the fundamental science that enables both of these projects, which are united by the importance of localized changes in polymer properties initiated by exposure to light.