Capillary forces acting at the air‐water interface play an important role in colloid fate and transport in subsurface porous media. We quantified capillary forces between different particles (sphere, cylinder, cube, disk, sheet, and natural mineral particles) and a moving air‐water interface. The particles had different sizes and contact angles (ranging from 14° to 121°). Theoretical calculations using the Young‐Laplace equation were used to support and generalize the experimental data. When the air‐water interface moved over the particles, there were strong capillary forces acting on the particles in the direction of the moving interface. The measured maximum capillary forces were similar to those calculated by the Young‐Laplace equation. The larger the contact angles and the larger the particle size, the stronger were the capillary forces. Particles with irregular shape and sharp edges experienced greater forces than smooth particles. Generalization of the results indicates that capillary forces exerted by a moving air‐water interface can readily exceed attractive Derjaguin‐Landau‐Verwey‐Overbeek (DLVO) and gravity forces for typical subsurface particles, and a moving air‐water interface is therefore an effective mechanism for mobilization of particles in porous media. Particles in the colloidal size range are particularly susceptible for mobilization by a moving air‐water interface.

The aim of this work is to derive sharp quantitative estimates of the qualitative convergence results developed by Li et al. (2015) for regularized full- and partial-cloaks through transformation optics approach. Let Γ₀ be a compact set in ℝ³ and Γ_δ be a δ-neighborhood of Γ₀ for δ∈ℝ₊. Γ_δ represents the virtual domain used for the blow-up construction. By incorporating suitably designed lossy layers, it is shown that if the generating set Γ₀ is a generic curve, then one would have an approximate full-cloak within δ² to the perfect full-cloak, whereas if Γ₀ is the closure of an open subset on a flat surface, then one would have an approximate partial-cloak within δ to its perfect counterpart. The estimates derived are independent of the contents being cloaked; that is, the cloaking devices are capable of nearly cloaking an arbitrary content. Furthermore, as a significant by-product, our argument allows the relaxation of the convexity requirement on Γ₀ by Li et al. (2015), which is critical for the Mosco convergence argument therein.