- Specific anion effects on the internal structure of a poly(N-isopropylacrylamide) brush. TJ Murdoch, BA Humphreys, JD Willott, GP Kasimir, SW Prescott, A Nelson, EJ Wanless and GB Webber. Macromolecules, 49(16), 6050–6060, 2016.
Abstract:
The effect of anion identity and temperature on the
internal nanostructure of poly(N-isopropylacrylamide) brushes were
investigated using neutron reflectometry (NR), atomic force
microscopy (AFM), and quartz crystal microbalance with
dissipation monitoring (QCM-D). NR and QCM-D measurements
showed that addition of strongly kosmotropic acetate anions shifted
the lower critical solution temperature (LCST) to lower temper-
atures relative to pure D2O/H 2O, while strongly chaotropic
thiocyanate anions shifted the LCST to higher temperatures.
Polymer density profiles derived from NR showed direct evidence of vertical phase separation at temperatures around the LCST
in all conditions. Results indicate that the density profiles were not simple modulations of structures observed in D2O to higher
or lower temperatures, with both anion identity and ionic strength found to influence the qualitative features of the profiles. In
particular, the presence of thiocyanate broadened the LCST transition which is attributed to the ability of the thiocyanate anion
to electrosterically stabilize the brush above its LCST. Complementary AFM data showed that the acetate ion induced collapsed
structures while a broader transition is observed in the presence of thiocyanate.
Last edited: Friday September 10, 2010
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