Creasing in evaporation-driven cavity collapse

Abstract

We report on crease morphology and evolution at the surface of contracting cavities embedded within elastomeric solids of varying composition (Sylgard 184: pre-polymer to crosslinker mixing ratios of 10 : 1, 12 : 1, 17.5 : 1, and 25 : 1). Cavity contraction is achieved through evaporation of an embedded 10 μL liquid droplet. In validation of recent theoretical predictions, strain-stiffening modeled via the Gent constitutive relation [Jin and Suo, JMPS, 2015, 74, 68-79] is found to govern both crease onset and crease density. Specifically, crease onset matches prediction using only experimentally-measured parameters. Neo-Hookean solids are found to prefer initiating creasing with many short creases that join to form a collapsed state with only a few creases, whereas creasing in Gent solids initiates with a few creases that propagate across the cavity surface. These experimental observations are explained by energy minimization using finite element simulation of a cylindrical crease geometry.

Extracting uncrosslinked material from low modulus sylgard 184 and the effect on mechanical properties

“…These elastomers are also common in fundamental research on soft matter physics and mechanics. For example, studies on soft adhesion, wetting, cavitation, and cell–surface interactions frequently implement PDMS as a model material. PDMS is used because it is commercially available (e.g., Sylgard 184), easy to prepare, and easy to tune the elastic modulus from a few megapascal down to a few kilopascal .…”

Turning Drops into Bubbles: Cavitation by Vapor Diffusion through Elastic Networks

“…In a somewhat different setup, Milner et al [12] studied the onset of creasing for droplets immersed in gels. In the present work, creases are observed below a critical radius R/R 0 = 0.73±0.05, in agreement with [12]. Finally, as the droplet further evaporates, a negative pressure builds up inside the drop due to the tensile stresses exerted on the cavity, ultimately leading to cavitation ( Fig.…”

Direct observation of pore collapse and tensile stress generation on pore walls due to salt crystallization in a PDMS channel

“…Noting that the halite (the crystallized form of sodium chloride) is anhydrous, the conclusion is that water leaves the collapsing region through pervaporation of water through the PDMS, e.g. [16][17][18][19][20]. Thus, as schematically illustrated in Fig.5, the picture is that water leaves the collapsing region by pervaporation through the PDMS while ions precipitate on the crystal.…”

“…The experiments have been performed several times with different configurations (geometry and initial concentration) and the hyperslow drying has always been observed. To explain the hyperslow evaporation depicted in Fig.3, it should be recalled that water can actually migrate into PDMS, [16][17][18][19][20]. Since the chip is first invaded by the solution during several minutes before the evaporation starts, the PDMS is actually saturated with water, at least near the pore channel and supply channel walls.…”

“…However, it has been shown, e.g. [18], that significant negative pressures can also be induced by the pervaporation process in a liquid pocket surrounded by PDMS. In our experiments, this would correspond to the situation where the crystal is in direct contact with the PDMS walls so as to hydraulically isolate the collapsing liquid plug.…”