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We investigate the wetting condition for diffuse-interface methods in the simulation of two-fluid flows with moving contact lines. A current method, which uses a surface-energy approach, is shown not to result in a slope of the interface that is consistent with the prescribed value of the contact angle. A geometric formulation is proposed that does result in the prescribed contact angle. Test results are presented for the axisymmetric droplet spreading due to the capillary force and the motion of a droplet on a solid substrate in a shear flow.

Computational methods have been extended recently to allow for the presence of moving contact lines in simulated two-phase flows. The predictive capability offered by these methods is potentially large, joining theoretical and experimental methods. Several challenges rather unique to this area need to be overcome, however, notably regarding the conditions near a moving contact line and the very large separation of length scales in these flows. We first summarize the main models for moving contact lines and follow with an overview of computational methods that includes direct continuum approaches and macroscale models that resolve only the large-scale flow by modeling the effects of the conditions near the contact line using theory. Results are presented for contact-line motion on ideal as well as patterned and grooved surfaces and for extensions to account for complexities such as thermocapillarity and phase change.

Recently, porous hydrophobic/oleophilic materials (PHOMs) have been shown to be the most promising candidates for cleaning up oil spills; however, due to their limited absorption capacity, a large quantity of PHOMs would be consumed in oil spill remediation, causing serious economic problems. In addition, the complicated and time-consuming process of oil recovery from these sorbents is also an obstacle to their practical application. To solve the above problems, we apply external pumping on PHOMs to realize the continuous collection of oil spills in situ from the water surface with high speed and efficiency. Based on this novel design, oil/water separation and oil collection can be simultaneously achieved in the remediation of oil spills, and the oil sorption capacity is no longer limited to the volume and weight of the sorption material. This novel external pumping technique may bring PHOMs a step closer to practical application in oil spill remediation.