Motion of Polymer Gels by Spreading Organic Fluid on Water

Abstract

We have constructed a new class of polymer gel that undergoes translational and rotational motions in water. These polymer gels consist of cross-linked hydrophobic−hydrophilic copolymers, which swell in water-miscible organic fluid but collapse in water. When these gels swollen in organic solvent are placed on supporting water, they start to do motion. The mode of motion depends on the shape of the gel: a disk- or spherical shaped gel exhibits translational motion while a triangular or a cubic one exhibits rotation. The velocity and duration of gel motion are strongly associated with its size and chemical structure. The driving force of the motion is originated from the surface spreading of organic solvent, which is pumped out of the gel because of the high osmotic pressure and hydrostatic pressure in the gel.