la400066d_si_001.pdf (429.87 kB)
Poly(N-isopropyl acrylamide) Brush Topography: Dependence on Grafting Conditions and Temperature
journal contribution
posted on 2013-05-14, 00:00 authored by B.-C. Choi, S. Choi, D. E. LeckbandThe
topography of poly (N-isopropyl acrylamide)
brushes end-grafted from initiator-terminated monolayers was imaged
by atomic force microscopy, as a function of the area per chain and
of solvent quality. Measurements were done in air and in water, below
and above the lower critical solution temperature. At low grafting
densities and molecular weights, area-averaged ellipsometry measurements
did not detect changes in the volume of water-swollen, end-grafted
polymer films above the lower critical solution temperature. However,
atomic force microscopy images revealed surface features that suggest
the formation of lateral aggregates or “octopus micelles”.
At high grafting densities and molecular weights, the films collapsed
uniformly, as detected by both AFM imaging and ellipsometry. These
findings reconcile in part prior results suggesting that some poly(N-isopropyl acrylamide) chains do not collapse in poor solvent,
and they also reveal more complex collapse behavior above the lower
critical solution temperature than is commonly assumed. This behavior
would influence the ability to tune the functional properties of poly(N-isopropyl acrylamide) coatings.