Experimental characterization of elastocapillary and osmocapillary effects on multi-scale gel surface topography

Abstract

Osmocapillary phase separation can pull solvent out from a gel surface and lead to length-dependent surface flattening. The osmocapillary flattening can be orders of magnitude larger than the existing studies of elastocapillary flattening.

Deformation-dependent gel surface topography due to the elastocapillary and osmocapillary effects

“…For simplicity, we assume the surface tension of the gel is identical to that of the solvent, which is valid for gels of high solvent content. 12,27 In gels of low solvent content, the gel surface stress can be different from the solvent surface tension and can be strain-dependent. 14,33,34…”

“…1–7 Smart surfaces that actively control surface behavior through surface topography have been extensively studied. For example, swelling a polymeric gel expands surface features, 8–12 and stretching a soft material deforms the surface topography with the bulk. 13–17 Although deforming a piece of material is simple, predicting the deformation-dependent surface topography is not.…”

“…13–17 Although deforming a piece of material is simple, predicting the deformation-dependent surface topography is not. 12,14,18 By elastic deformation alone, stretching the material flattens surface topography due to the Poisson effect. However, if the material is sufficiently soft, surface tension can deform the surface topography, causing elastocapillary deformation.…”

“…14,17–22 If the material is sufficiently swollen with a solvent, surface tension can pull the solvent out from the material bulk, leading to osmocapillary phase separation. 12,23–25 While the elastocapillary and osmocapillary effects on a static surface are relatively well studied, how they affect surface topography during deformation remains unclear. Understanding the deformation-dependent elastocapillary and osmocapillary effects is crucial to predicting the deformation-dependent surface topography and designing novel smart surfaces.…”

“…The change under volumetric deformation have been recently reported. 12 We perform novel finite element simulation that incorporates coupled elastocapillary and osmocapillary effects. We use a sinusoidal profile to reveal the length dependence of the elastocapillary and osmocapillary effects.…”