Relaxation back to equilibrium after cessation of shear for confined colloidal bilayers
msra(2005)
摘要
Crystalline bilayers of charged colloidal suspensions which are confined
between two parallel plates and sheared via a relative motion of the two plates
are studied by extensive Brownian dynamics computer simulations. The
charge-stabilized suspension is modeled by a Yukawa pair potential. The
unsheared equilibrium configuration are two crystalline layers with a nested
quadratic in-plane structure. For increasing shear rates $\dot \gamma$, we find
the following steady states: first, there is a static solid which is
elastically sheared until a yield-stress limit is reached. Then there are two
crystalline layers sliding on top of each other with a registration procedure.
Higher shear rates melt the crystalline bilayers and even higher shear rates
lead to a reentrant solid stratified in the shear direction. This qualitative
scenario is similar to that found in previous bulk simulations. We have then
studied the relaxation of the sheared steady state back to equilibrium after an
instantaneous cessation of shear and found a nonmonotonic behavior of the
typical relaxation time as a function of the shear rate $\dot \gamma$. In
particular, application of high shear rates accelerates the relaxation back to
equilibrium since shear-ordering facilitates the growth of the equilibrium
crystal. This mechanism can be used to grow defect-free colloidal crystals from
strongly sheared suspensions. Our theoretical predictions can be verified in
real-space experiments of strongly confined charged suspensions.
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关键词
steady state,materials science,colloidal suspension,brownian dynamics,computer simulation,relaxation time,shear rate,yield stress
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