RESUMO
A model for the dynamic contact angles and the spreading kinetics of nematic liquid crystals on a solid surface is presented for the first time using the continuum theory of liquid crystals. The equations of motion for this system are integrated for a wedge or a drop that is thin and moves slowly. The dynamic contact angle is found to depend on the capillary number that represents the importance of viscocapillarity and on the elasticity number that is the ratio between the elastic and surface forces. The model provides an explanation for the extra volume dependence that is reported in experiments, as well as one case of recoil, and for the observation that very small drops were reported to be immobile. For the first time, these previous experimental observations are shown to be due to elastic effects.
RESUMO
Polymer flooding is an important process in enhanced oil recovery. The displacement front is unstable when low viscosity brine displaces the heavy crude oil in the reservoir. Water-soluble polymers are added to the brine to increase its viscosity which stabilizes the displacement process. To analyze the displacement process at the micro-level, we have investigated the dynamic contact angles in silicone oil-polymer (polyethylene oxide) solution and for the first time. The dynamic contact angle is the apparent contact angle at the three-phase contact line which governs the capillary pressure, and thus is important for the displacement process. The data show no obvious signs of either shear thinning or elastic behavior, although for some systems with highest elastic effects some unexplained effects on dynamic contact angles are observed that correlate with elastic effects. Overall, dynamic contact angles are explained well using existing models for two Newtonian fluids, when the zero shear viscosity is used for the polymer solution.
