Late stage dynamics of phase separation processes of binary mixtures containing surfactants

Abstract

Late stage dynamics of phase separation processes of immiscible binary mixtures containing surfactants (amphiphilic molecules) is investigated by computer simulations on the hybrid model proposed by the present authors [T. Kawakatsu and K. Kawasaki, Physica A 167, 690 (1990)]. With use of this hybrid model, one can investigate large scale phenomena while retaining the intramolecular structures of surfactant molecules. Simulations are performed both for irregular bicontinuous and micellar domain formation processes taking the thermal fluctuation effects into account. In the very late stage, the coarsening of the domain structures is considerably slowed down both for bicontinuous and micellar domain formation processes due to the low interfacial tension of the surfactant-adsorbed interfaces. Scaled scattering structure functions are also calculated, which possess the characteristic features of the experimentally observed scattering functions of microemulsions and polymer blends containing amphiphilic block copolymers. We found that the calculated structure function for the system containing surfactants is different from that for the simple binary mixture without surfactant. Also reported are the important effects of thermal fluctuations on micellar domain structures, where the domain formation is considerably accelerated by the thermal fluctuation. 8200

Lattice-Boltzmann model for interacting amphiphilic fluids

“…Interestingly, this happens much faster than in the case of the binary system. The presence of the surfactant seems to accelerate domain formation in the early stage of phase separation, an effect which has also been seen in the hybrid Ginzburg-Landau simulations of Kawakatsu et al [35], and should be detectable experimentally. As time evolves the peak in S(k, t) increases in height and shifts further towards smaller values of the wavelength, indicating the growth of droplets.…”

A lattice-gas model of microemulsions

“…The complex nature and wide industrial application of these systems make them ideal subjects for experimental, theoretical and numerical investigation. Most previous work in this area has been done on the equilibrium phase behaviour (Gompper & Schick 1995) of such self-assembling systems; comparatively little research has been devoted to their nonequilibrium, dynamic properties (Kawakatsu et. al 1993).…”

“…In this paper we develop a version of such a model that simulates the nonequilibrium, dynamical properties of amphiphilic systems, and in particular of microemulsions. Note that the use of the basic lattice gas model, in contrast to, for example, molecular dynamics simulations, gives us the ability to investigate the important late-time dynamics of these systems (Kawakatsu et al 1993) in a computationally tractable manner. Also, since lattice-gas models enable the implementation of complex boundary conditions, we can simulate very realistic interface formation and dynamics and investigate such systems under flow and within complex media such as porous rock.…”

Lattice-gas simulations of minority-phase domain growth in binary immiscible and ternary amphiphilic fluids

“…Instead, the requirement that surfactant molecules sit at oil-water interfaces will lead to a saturation of domain growth. Previous work studied the domain growth using numerical integration of Landau-Ginzburg models, for example the hybrid model of Kawakatsu et al 21 and the twolocal-order parameter model of Laradji and coworkers 22,23 . These models do not include hydrodynamic effects and find that surfactant modifies the kinetics from the binary n = 1 3 algebraic exponent to a slow growth that may be logarithmic in time.…”