Aging in dense suspensions of soft thermosensitive microgel particles studied with particle-tracking microrheology

Dirk van den Ende, Eko H Purnomo, Michel H.G. Duits, Walter Richtering, Frieder Mugele

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Abstract

Using particle tracking microrheology, we studied the glass transition in dense suspensions of thermosensitive microgel particles. These suspensions can be tuned reversibly between the glass state at low temperature and the liquid state at high temperature. In the glass state, the ensemble averaged mean squared displacements (MSDs) of added fluorescent tracer particles depend on the age of the suspension. We also determine the local viscoelastic moduli, G′ and G″, from the MSDs using the Generalized Stokes-Einstein Relation and compare them to the bulk moduli, measured using conventional rheometry. With particle tracking, one probes the viscoelastic moduli in a lower frequency range than with macrorheology, which makes it possible to determine the mean relaxation time that is inaccessible with macrorheology. In the glass state, the mean relaxation time increases linearly with the age of the sample and the short time particle displacement distributions are non-Gaussian, indicating inhomogeneity of the system. The observed difference between conventional and microrheology is explained quantitatively assuming that the tracer particles are surrounded by a viscoelastic liquid shell, different from the bulk.
Original languageEnglish
Article number011404
Number of pages9
JournalPhysical review E: Statistical, nonlinear, and soft matter physics
Volume81
Issue number1
DOIs
Publication statusPublished - 2010

Keywords

  • IR-69508

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