Light-induced shape recovery of deformed shape memory polymer micropillar arrays with gold nanorods

Abstract

We prepared light-responsive shape memory polymer (SMP) micropillars (10 μm in diameter, 40 μm in height, and 20 μm in pillar-to-pillar distance) in a hexagonal array mixed with 0.1–0.2 mol% gold nanorods (AuNRs) by replica molding from a poly(dimethylsiloxane) (PDMS) mold. The addition of AuNRs did not change the glass transition temperature (T_g) of SMPs much, for example, from 47.8 °C (pristine SMP) to 42.1 °C (SMP with 0.2 mol% AuNRs). The pillars were bent to different angles by controlling the force applied on top of the sample above its T_g, followed by cooling down to room temperature to lock the deformed structures. The bent pillars were nearly completely recovered to the straight ones when exposed to a visible laser. Recovery time as small as 5 s from 0.3 W green laser was demonstrated, depending on the loading of AuNRs, the bending angle, the T_g of composite material, and exposure dosage. Between bent and straight pillars, we demonstrated tunable transmittance in the visible wavelength and water contact angle from 160° (straight pillars) to 100° (completely collapsed pillars).