Asymmetric water diffusion driven nanotube actuator

Abstract

Here we report, water vapor driven actuation of polymer nanotubes, embedded in a nanoporous membrane with one end attached to a surface deposited thin polymer layer. The nanotube composite shows oscillatory motion when placed near water. Permeation of water vapor through these nanotube embedded membranes is found to be direction dependent. With the water vapor as the driving force, the actuator can lift a mass 1000 times heavier than itself with a change in relative humidity of less than 40%. The actuation mechanism arises due to efficient absorption of water molecules by polymer nanotubes and their rapid evaporation through the surface deposited polymer layer. This actuator can be used as artificial muscle and the direction dependent water transport may help in understanding the activities of transmembrane channels and pumps of biological cells. With the aid of a nanowire generator, the oscillatory motion can be used to generate electricity too.