Woodward, Nicola C., Chowdhry, Babur Z., Snowden, Martin J. ORCID: https://orcid.org/0000-0002-1087-2692, Leharne, Stephen A., Griffiths, P.C. ORCID: https://orcid.org/0000-0002-6686-1271 and Winnington, Angie L. (2003) Calorimetric investigation of the influence of cross-linker concentration on the volume phase transition of poly(N-isopropylacrylamide) colloidal microgels. Langmuir, 19 (8). pp. 3202-3211. ISSN 0743-7463 (Print), 1520-5827 (Online) (doi:10.1021/la020881i)

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Abstract

A series of poly(N-isopropylacrylamide) microgels were prepared, by a surfactant-free emulsion polymerization method, incorporating varying cross-linker concentrations (0.25-30.0% of N,N'-methylenebisacrylamide). Turbidimetric, light scattering, and differential scanning calorimetric (DSC) analyses of aqueous dispersions of these microgels show that the temperature and the half-width of the overall volume phase transition (VPT) of the colloidal dispersions increase with increasing cross-linker concentration. DSC analysis also reveals a decrease in the overall calorimetric enthalpy of the VPTs with increasing cross-linker concentration. The DSC thermograms have been deconvoluted into two component transitions; one is asymmetric and attributed to aggregation of "free" N-isopropylacrylamide monomers/oligomers, and a second, two-state conformational transition, is associated with the cross-linked microgels. Pulsed-gradient spin-echo NMR diffusion measurements show that the diffusion of water within the particles can be estimated and this diffusion rate decreases with increasing cross-link concentration. Complementary fluorescence studies show an increased hydrophobicity as the cross-linker density increases.

Item Type:	Article
Uncontrolled Keywords:	n-isopropylacrylamide, particles, macromolecules, polymerization, chains
Subjects:	Q Science > QD Chemistry
Faculty / School / Research Centre / Research Group:	Faculty of Engineering & Science
Related URLs:	Publisher
Last Modified:	16 Apr 2020 13:26
URI:	http://gala.gre.ac.uk/id/eprint/4888

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