Abstract
Apratim Chatterji: „Dynamics of Ultra-Soft Colloids (Star Polymers) under Shear”
IFF Jülich
We study the dynamics, structure formation, and jamming transitions of
ultrasoft colloidal particles under shear. We consider a star polymer as
a
model system of a colloid with variable softness. The center of a star
polymer with a large number of polymer arms f, has a very dense core
and, hence, behaves like a rigid colloidal object. The softness
can
be tuned by varying f as well as the number of monomers N in the
individual polymer arms. The transition from polymer-like properties to
rigid-colloid like behaviour as a function of f of stars has been
investigated previously {1,2}. We now study the effect
of packing many star polymers for fixed f and N. Under equilibrium
conditions we find that increased packing reduces the effective size of
the stars. Under steady state shear, however, the higher packing of
stars
enhances shear
induced deformation of stars as well as increased allignment of the
deformed stars with the flow direction.
We have observed shear thinning behaviour at high shear rates. We are
investigating the possibility of jamming phenomenon for soft
colloids/star
polymers at higher arm number f.
We use a bead-spring potential with explicit excluded volume
interactions
to model the monomers of the star polymer. Hydrodynamic interactions are
incorporated by coupling the star polymers to a MPC (multi-particle
collision) fluid which is a coarse grained description of the solvent.
References
- M. Ripoll, R. G. Winkler, G. Gompper, Phys. Rev. Lett. 96, 188302, (2006).
- M. Ripoll, R. G. Winkler, G. Gompper, Eur. Phys.J.E, 23, 349 (2007).