Phase-field simulations of precursor film in microcapillary imbibition for liquid-liquid systems

ABSTRACT Precursor film flow has been extensively studied on flat surfaces in Liquid-Gas systems. However, its effects in capillary imbibition processes, especially in Liquid-Liquid systems, are lack investigation. Using the phase-field method, this work simulates microcapillary imbibition processes in strong imbibition regimes with the viscosity ratio magnitude from 10−1 to 10. The numerical model is first tuned with a prescribed contact angle of 30o under which the precursor film is less likely occurs. The model validation results indicate that simulation accuracy of microcapillary imbibition is more sensitive to the Cn number and the model length than the mobility tuning parameter and viscosity ratio. After that, we discussed the effects of contact angle and viscosity ratio on imbibition processes considering precursor film. 25o is the critical contact angle for occurring the precursor film in the capillary filling. Compared with the contact angle, the effects of the viscosity ratio on film flow is limited. Though the viscosity ratio effects are considered in the Cox-Voinov model by solving the power-law approximations of the integrand, the simulated dynamic contact angle is still observed lower than the theoretical values because of the precursor film. Moreover, it also found that the simulated dynamic contact angle could reach a value lower than the static contact angle in tested unfavorable viscosity ratios. The significant effects of precursor film make the simulated total imbibition time roughly 10% to 20% less than the theoretical imbibition time without considering precursor film flow.