Structure and rheology of binary mixtures in shear flow

Area of Science:

• Physics
• Materials Science
• Soft Matter

Background:

• Phase separation is crucial in materials science for tuning properties.
• Understanding kinetics under external fields like shear flow is essential for controlling microstructure.
• The time-dependent Ginzburg-Landau equation is a standard model for studying phase transitions.

Purpose of the Study:

• To investigate the phase separation kinetics of a binary mixture under uniform shear flow.
• To analyze the influence of stationary and oscillating shear on domain growth and structure.
• To characterize the dynamical scaling and excess viscosity behavior during shear-induced phase separation.

Main Methods:

• Utilizing the time-dependent Ginzburg-Landau equation with an external velocity term.
• Employing the large-n approximation to solve the model equations.
• Analyzing the structure factor and excess viscosity for stationary and oscillating shear flows.

Main Results:

• Anisotropic domain growth observed under stationary shear, with different scaling exponents in and perpendicular to the flow direction (Rx ~ t^(5/4), R⊥ ~ t^(1/4)).
• Excess viscosity shows relaxation behavior and exhibits logarithmic-time periodic oscillations attributed to cyclic domain stretching and breakup.
• Under oscillating shear, an initial crossover to stationary flow behavior is followed by isotropic growth, similar to the un-sheared case.

Conclusions:

• Shear flow significantly alters phase separation dynamics, inducing anisotropic growth and oscillatory behavior.
• The observed oscillations in excess viscosity provide insights into the cyclical nature of domain evolution under shear.
• The study highlights the distinct effects of stationary versus oscillating shear on the late-stage morphology of phase-separating mixtures.