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Drying is a crucial step
in the processing of a variety of materials, from the common coat of paint
to emerging photonic band-gap structures. As the suspending fluid evaporates,
fracture, delamination, and buckling can ruin the material. Profs. Weitz,
Hutchinson and Xie have been exploring drying nanoparticle suspensions,
which are particularly prone to fracture. In the nanoparticle regime,
drying stresses, originating from the affinity of the fluid for suspended
particles, can exceed 1000 times atmospheric pressure. Furthermore, the
fluid immersing nanoparticles can behave strangely. Since the gaps between
tightly packed nanoparticles are only a few molecules across, fluid molecules
can be arrested by strong short-range interactions with the nanoparticles.
Recently MRSEC REU students have demonstrated the importance of these
molecular-scale interactions on the macroscopic dynamics of drying nanoparticle
suspensions (to appear in Physical Review Letters). |