A comparison between liquid drops and solid particles in partial wetting

Abstract

In this critical review we compare two geometries in partial wetting: a liquid drop on a planar substrate and a spherical particle at a planar liquid interface. We show that this comparison is far from being trivial even if the same physical interactions are at play in both geometries. Similarities and differences in terms of free energies and frictions will be discussed. Contact angle hysteresis, the impact of surface roughness and line pinning on wetting will be described and compared to selected experimental findings.

Motion of micro- and nano- particles interacting with a fluid interface

“…A solid colloidal particle at a fluid interface in a partial wetting state is usually trapped in a surface energy well [46] [47]. The order of magnitude of the energy well can be roughly estimated by the surface energy of the portion of the fluid interface occupied by the particle: = 2 (for a spherical particle with a 90° wetting contact angle , see figure 3), where is the fluid interfacial tension and the particle radius.…”

Rotational diffusion of partially wetted colloids at fluid interfaces

“…A solid particle straddling an interface should not be simply seen as a geometrical object partially immersed in a liquid but rather as an intriguing partial wetting configuration. For colloidal microparticles, the fluid interface deformation due to gravity or other external fields is usually weak and the solid particle immersion is set by an equilibrium contact angle in analogy with the partial wetting of a sessile drop on a solid substrate [1]. This configuration, however, should not be considered static since both the colloidal particle and the contact line are subjected to thermal agitation, which results in the particle Brownian motion and in the displacement of contact line back and forth around some equilibrium position [2].…”

Assessment of nanoparticle immersion depth at liquid interfaces from chemically equivalent macroscopic surfaces

“…The former is expressed as the capillary length ((l c =@γ Δρg ⁄ ), where γ is the surface/interfacial tension, Δρ the liquid density difference and g the gravitational acceleration), which is around 2.71 mm in air/water and 4.44 mm for decane/water, while the latter operates below a characteristic length scale l s =θ E -2 @H 6πγ ⁄ ≈ 1-10 nm, θE is the ECA, and H is the Hamaker constant. If the principal radii are smaller than lc, gravitational forces do not influence the shape of the droplet or interface for sessile droplets or adsorbing colloids, respectively [84]. The sessile drops in this study on the substrates and the NP size are well below lc and above ls.…”