Shape-Shifting Polymer Gels
Polymer gels are remarkable, shape-shifting materials. When
exposed to small alterations in acidity or temperature, for
instance, they can dramatically transform their appearance and
size. The secret to this trick is that forces between
molecules in the gels are delicately balanced in a constant
tug-of-war. Anything that strengthens electrostatic or
hydrophobic repulsion within these gels will make them expand;
influences building attraction, typically mediated by hydrogen
bonding or van der Waals interactions, will make them shrink.
Unfortunately, inducing these changes with accuracy or speed
has proved difficult. But in today's issue of Nature,
researchers from the University of Tokushima in Japan describe
a new, incredibly precise tool for morphing polymer gels:
Hiroaki Misawa and colleagues focused a laser beam at the
center of a cylinder of N-isopropylacrylamide (NIPAM) and
found that within an instant, the rod's middle shrank in
diameter, turning it into a dumbbell. When they shut the laser
off, the middle snapped back to its original width. To
demonstrate that radiation forces from the laser, and not
temperature, were at work, they also illuminated the gel for
several minutes with a weak laser, having insufficient
strength to shrink it. The gel didn't change, which would have
been the case had the heat built up. Because the
transformations in the gels are entirely reversible and the
light can be so precisely targeted, a number of
applications--though far off--are possible, including
gel-laser-based actuators and sensors.
Archive date: 11-09-00
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