String Phase in Phase-Separating Fluids under Shear Flow

Thermodynamic coarsening arrested by viscous fingering in partially miscible binary mixtures

“…For instance, hydrodynamic coalescence due to curvature-induced pressure differences can enhance the coarsening rate [5,6]. Under uniform shear flow, a highly anisotropic layered phase ordering appears in the mixture [7][8][9]. Under turbulent flow, experiments [10,11] and numerical simulations [12,13] have shown that coarsening is suppressed due to vigorous stirring, a result that is also observed when a chaotic flow is imposed [14].…”

Computation of multiphase systems with phase field models

“…Here the structures are much more complex with plates and strings forming. Stringlike structures have been observed in polymer blends which are thermodynamically near a phase transition point [37,38] and in immiscible viscoelastic systems in complex flow fields [39] and in dispersed droplets [39]. There is great current interest in micro and nano lengthscale technologies in which polymer blends could play an important role.…”

“…The Cahn number represents the ratio between the interface thickness and the domain size. Characteristic properties of (38) are the conservation of the order parameter [12] …”

Effect of shear flow on the stability of domains in two-dimensional phase-separating binary fluids

“…This is surprising, since a long cylinder of fluid at rest would normally break up via the Rayleigh instability [15,16], a hydrodynamic instability. The string phase appears to be a fairly robust phenomenon, appearing in both critical and off-critical polymer mixtures [13] and in critical micellar solutions [17]. Thus, the shear flow both opposes the thermodynamic instability driving phase separation and stabilizes these highly anisotropic domains against hydrodynamic instabilities.…”

“…In relatively weak shear, the domains are somewhat deformed, whereas at higher shear they can become highly elongated along the flow direction. A "string phase" consisting of macroscopically long cylindrical domains forms when the two phases are both percolated [13,14]. This is surprising, since a long cylinder of fluid at rest would normally break up via the Rayleigh instability [15,16], a hydrodynamic instability.…”