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

We prepared light-responsive shape memory polymer (SMP) micropillars (10 mu m in diameter, 40 mu m in height, and 20 mm 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 degrees C (pristine SMP) to 42.1 degrees 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 degrees (straight pillars) to 100 degrees (completely collapsed pillars).