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Influence of molecular weight on PNIPAM brush modified colloidal silica particles

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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.

Graphical abstract: Influence of molecular weight on PNIPAM brush modified colloidal silica particles

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Publication details

The article was received on 07 Sep 2018, accepted on 02 Dec 2018 and first published on 03 Dec 2018


Article type: Paper
DOI: 10.1039/C8SM01824C
Citation: Soft Matter, 2019, Advance Article
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    Influence of molecular weight on PNIPAM brush modified colloidal silica particles

    B. A. Humphreys, S. W. Prescott, T. J. Murdoch, A. Nelson, E. P. Gilbert, G. B. Webber and E. J. Wanless, Soft Matter, 2019, Advance Article , DOI: 10.1039/C8SM01824C

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