Figure 4: Comparison of photothermal and thermal actuation.

Representative top-view images of HAIRS-xNR samples showing different modes of actuation. The two central images show HAIRS samples before actuation, where the central top image corresponds to a HAIRS-30NR sample and the bottom image corresponds to a HAIRS-0NR sample containing no nanorods (control). The left column represents homogeneous heating and cooling cycles of samples using a hot plate. The right column shows photothermally triggered localized heating and actuation (laser power ∼18 mW). In either experiment, the increase in temperature above the hydrogel LCST results in the contraction of the hydrogel and the bending actuation of the micro-plates, which appear as a pattern of overlapping tiles when viewed from the top. In the homogeneous heating and cooling cycles using a hot plate, all of the microplates actuate in both the HAIRS-30NR and the HAIRS-0NR samples displaying no localized effects. The NIR light exposure of the HAIRS-30NR sample produces the actuation/bending of the microplates only within the irradiated region. The pink dashed circle in the upper right image marks the area where the microplates are actuated. No actuation or bending was observed following localized NIR irradiation of HAIRS samples not containing AuNR. All scale bars are 10 μm.