|dc.description.abstract||The lattice Boltzmann (LB) method is a versatile way to model complex fluids
with hydrodynamic interactions through solving the Navier-Stokes equations. It is
well-known that the role of hydrodynamic interactions is ignorable in studying the
Boltzmann equilibrium of colloidal (Brownian) particles. However, full hydrodynamic
interactions play an important role in their dynamics. In the LB framework for moving
colloids, the “bounce-back on links” method is used to calculate the hydrodynamic
forces. In this thesis, three kinds of colloidal complex fluids with full hydrodynamic
interactions are simulated by lattice Boltzmann methods: colloids in a binary fluid,
magnetic colloids in a single fluid and magnetic colloids in a binary fluid.
First, we have done extensive simulations of nanoparticles in a binary fluid, following
up previous work which predicted formation of a “bijel” (bicontinuous interfacially
jammed emulsion gel) in symmetric fluid quenches. Our work in this thesis focuses
on the analysis of the dynamics after nanoparticles become arrested on the fluid-fluid
interfaces under conditions varying from a symmetric quench to a strongly asymmetric
quench. Although these new simulations extend the time window studied by a factor
of two, slow domain growth is still observed. Our new analyses address the mechanics
of the slow residual dynamics which involves cooperative motion of the nanoparticles
at the fluid-fluid interfaces.
The second topic is the LB simulation of colloidal ferrofluids to see the effect
of full hydrodynamic interactions among magnetic colloids. The main focus is on
how the hydrodynamic interaction affects both the equilibrium dynamics of these
dipolar systems and also their transient dynamics to form clusters. Numerically,
magnetic colloids are implemented with the long-range dipolar interactions described
by Ewald summation. To check the effect of full hydrodynamic interactions, Brownian
dynamics without any hydrodynamic interaction has been done for comparison: Monte
Carlo results are also reported. We confirm that our LB generates the Boltzmann
distribution for static equilibrium properties, by comparison with these methods.
However, the equilibrium dynamics is altered: hydrodynamic interactions make the
structural relaxations slower in both the short-time and the long-time regime. This
slow relaxation rate is also found for transient motions.
The third topic addresses magnetic colloids in a binary fluid. In contrast with
the preceding two systems which correspond directly to laboratory experiments, this
last system is so far only predicted by the LB results in this thesis. To explore this
hypothetical new material by the LB method, the basic structures are investigated in
terms of both domain growth morphology and the arrangement of magnetic colloids.
Under conditions varying from a symmetric quench to an asymmetric quench, a
chainlike arrangement is observed for dipoles jammed on the surfaces, but the basic
morphology of domains is still maintained regardless of the dipolar strength. In
addition, applying external field affects the morphology of domains and the stability of domain structures.||en