Berlin 2015 – wissenschaftliches Programm
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DY: Fachverband Dynamik und Statistische Physik
DY 41: Complex Fluids and Soft Matter - Part II (joint session DY/ CPP / BP)
DY 41.6: Vortrag
Donnerstag, 19. März 2015, 11:00–11:15, BH-N 334
Transient microrheology of viscoelastic fluids — •Juan Ruben Gomez Solano1,2 and Clemens Bechinger1,2 — 12. Physikalisches Institut, Universitaet Stuttgart, Pfaffenwaldring 57, 70569 Stuttgart, Germany — 2Max-Planck-Institute for Intelligent Systems, Heisenbergstrasse 3, 70569 Stuttgart, Germany
Viscoelasticity is ubiquitous in soft matter ranging from biological fluids to new synthetised materials, whose mechanical response deviate from Newtonian behavior under applied stress or strain. Microrheology has proved successfully in recent years as an alternative to bulk rheology in investigating linear and steady-state flow properties of microlitre samples of such materials. More complex transient behavior, e.g. creep and strain recovery after flow startup and cessation, is far less well understood within the context of microrheology. In this work we experimentally study the transient motion of a colloidal particle actively dragged by an optical trap through different viscoelastic fluids (wormlike micelles, polymer solutions, and entangled lambda-phage DNA). We observe that, after sudden removal of the moving trap, the particle recoils due to the relaxation of the deformed fluid microstructure until its complete strain recovery. We find that the relaxational dynamics of the particle proceeds via a double exponential decay, whose relaxation times remain independent of the initial particle velocity whereas their amplitudes strongly depend on it. We show that this transient information, which has no counterpart for colloids moving in Newtonian fluids, can be exploited to determine linear and non-linear flow properties of the embedding fluid.