Computer simulations of microrheology in dense colloidal systems

Condensed Matter lunchtime seminar

Computer simulations of microrheology in dense colloidal systems

  • Event time: 1:00pm
  • Event date: 26th March 2008
  • Speaker: Antonio M. Puertas (University of Almeria)
  • Location: Room 2511,

Event details

Using Brownian dynamics simulations ,the microrheology of hard colloids was studied by dragging one particle, trapped in a parabolic external potential, through the system. Different trap velocities and colloidal densities are studied. From the distribution of displacements of the dragged particle inside the trap, an effective viscosity of the system and its effective temperature can be determined. For small trap velocities, the system relaxes the external stress faster than the trap motion; thus, the effective viscosity is independent on the velocity and the temperature is equal to that of the thermal bath. For higher velocities, however, the trapped particle moves faster than the relaxation of the fluid and induces stress, which results in higher effective temperature, as well as lower viscosity. At very high velocity, the viscosity becomes constant again, but the temperature increases as $\sim v_{trap}^2$. This behaviour resembles the macroscopic rheology of a colloidal system, with quantitative agreement in some aspects, particularly, in the low velocity viscosity compared to the shear viscosity of the system. The Fluctuation Theorem will be also studied by means of the distribution of work done on the particle. Finally, the density profiles around the particle will also shown and discussed.

This is a weekly series of informal talks given primarily by members of the soft condensed matter and statistical mechanics groups, but is also open to members of other groups and external visitors. The aim of the series is to promote discussion and learning of various topics at a level suitable to the broad background of the group. Everyone is welcome to attend..

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