- Influence of Molecular Weight on PNIPAM Brush Modified Colloidal Silica Particles. BA Humphreys, SW Prescott, TJ Murdoch, A Nelson, E Gilbert, GB Webber and EJ Wanless. Soft Matter, 15, 55–64, 2019.
Abstract:
The effect of molecular weight and temperature on the phase transition and internal structure of
poly(N-isopropylacrylamide) brush modified colloidal silica particles was investigated using dynamic light scattering (DLS)
and small angle neutron scattering (SANS) between 15 and 45 °C. Dry particle analysis utilising transmission electron
microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR) and thermogravimetric analysis (TGA) all confirmed the
thickness of the polymer brush shell increased as a function of polymerisation time. Hydrodynamic diameter and
electrophoretic mobility results revealed that the brush modified particles transitioned from swollen shells to a collapsed
conformation between 15 and 35 °C. The dispersions were electrosterically stabilised over the entire temperature range
investigated, with minimal thermal hysteresis recorded. Modelling of the hydrodynamic diameter enabled the calculation
of a lower critical solution temperature (LCST) which increased as a function of brush thickness. The internal structure
determined via SANS showed a swollen brush at low temperatures (18 and 25 °C) which decayed radially away from the
substrate, while a collapsed block-like conformation with 60% polymer volume fraction was present at 40 °C. Radial phase
separation was evident at intermediate temperatures (30 and 32.5 °C) with the lower molecular weight sample having a
greater volume fraction of polymer in the dense inner region at these temperatures.
Last edited: Friday September 10, 2010
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