Our buildings waste energy in an endless cycle of heating and
cooling. We mammals, however, have our own (low-cost) method of
temperature regulationy sweating. The front cover of this issue
of Advanced Materials (Issue 39, Volume 24) nicely illustrates a
great new idea for smart materials in the real world: using
sweating polymers to passively cool buildings. Prof. W. J. Stark
and his co-workers wondered if a thermoresponsive material,
PNIPAM, poly-N-isopropylacrylamide, could be used to keep a
model house cool. PNIPAM has a lower critical solution
temperature of 32 °C. Below that temperature the polymer is
well-swollen and hydrophilic; above that temperature the polymer
collapses to a hydrophobic state, “sweating” out water in the
process. In an initial experiment, the researchers took two
identical model houses and replaced their roofs: one with a roof
made from 3-mm-thick layers of partially crosslinked PNIPAM and
the other with a roof made from a conventional hydrogel: poly-
hydroxyethylmethacrylate (HEMA)