Eur. Phys. J. E (2014) 37: 44
https://doi.org/10.1140/epje/i2014-14044-y

Regular Article

A microrheological study of hydrogel kinetics and micro-heterogeneity

¹ Cavendish Laboratory, Department of Physics, University of Cambridge, JJ Thomson Avenue, Cambridge, CB3 0HE, UK
² Unilever R&D Colworth, Colworth Science Park, Sharnbrook, Bedford, MK44 1LQ, UK

^* e-mail: A.Aufderhorst-Roberts@leeds.ac.uk

Received: 19 October 2013
Revised: 31 January 2014
Accepted: 20 March 2014
Published online: 27 May 2014

Abstract

The real-time dynamic heterogeneity of the gelation process of the amino acid derivative Fmoc-tyrosine (Fmoc-Y) is studied using particle tracking microrheology. To trigger gelation, glucono-δ-lactone (GdL) is added, which gradually lowers the p H over several hours. The onset of self-assembly in the system is signified by a sharp drop in the mean-squared displacement of embedded particles, a phenomenon that is found to correlate with the p H of the system reaching the pK_a of Fmoc-Y. The gel point is identified and found to be dependent on the GdL concentration. Analysis of embedded probe particle dynamics allows the heterogeneity of the sample to be quantified, using three metrics: the heterogeneity ratio (HR), the non-Gaussian parameter of the van Hove correlation function (N and the bin distribution of the mean-squared displacement (MSD) of single particles (f (z). Results from the three techniques are found to be approximately comparable, with increases in heterogeneity observed in all samples for incubation times t _w = 0 -3 hours. The final heterogeneity in all samples is found to be remarkably low compared to other systems previously reported in the literature.