Kinetics of Light‐Responsive CNT / PNIPAM Hydrogel Microactuators

Abstract Light‐responsive microactuators composed of vertically aligned carbon nanotube (CNT) forests mixed with poly(N‐isopropylacrylamide) (PNIPAM) hydrogel composites are studied. The benefit of this composite is that CNTs act as a black absorber to efficiently capture radiative heating and trigger PNIPAM contraction. In addition, CNT forests can be patterned accurately using lithography to span structures ranging from a few micrometers to several millimeters in size, and these CNT‐PNIPAM composites can achieve response times as fast as 15 ms. The kinetics of these microactuators are investigated through detailed analysis of high‐speed videos. These are compared to a theoretical model for the deswelling dynamics, which combines thermal convection and polymer diffusion, and shows that polymer diffusion is the rate‐limiting factor in this system. Applications of such CNT/hydrogel actuators as microswimmers are discussed, with light‐actuating micro‐jellyfish designs exemplified, and >1500 cycles demonstrated.