Film Instability Induced by Swelling and Drying

Abstract

Poly(2-vinyl pyridine), P2VP, films display a surface pattern of craters in a dried state after being immersed in aqueous solutions containing HAuCl4 and its mixtures with low contents of K2CO3. The morphologies of craters indicate that the formation of craters involves three stages through film blistering and drying: (i) the permeability of water and solutes to swell P2VP films, (ii) partial wetting of liquid droplets near the substrate interface in the presence of the P2VP film, and (iii) evaporation-driven flows. The three stages produce the swelling pressure, Laplace pressure, and interplays among capillary flows, Marangoni flows, and pinning effects, respectively, by which craters of different dimensions and morphologies are obtained. The first stage softens the P2VP films and produces swelling pressure. This stage relies on interactions between AuCl4 – ions, water, and protonated P2VP chains. The second stage produces liquid droplets inside the film and near the substrate interface. The surface tensions of those liquid droplets at contact lines deform swollen P2VP films. Changing film thicknesses or substrate types alters craters’ lateral dimension and depth. The results indicate that film thicknesses and substrate interface energies influence the shape and dimension of liquid droplets on the substrate interface. The third stage determines morphologies of craters through interplays among capillary flows, Marangoni flows, and pinning/depinning events.

Hierarchical Surface Instability in Polymer Films

“…40−47 Surface wrinkling and surface cratering have been reported in our previous studies, respectively. 10,30 The surface wrinkling was obtained when poly(4-vinylpyridine) (P4VP) films were immersed in an aqueous solution consisting of HAuCl 4 in water. 30 The surface wrinkling is due to the swelling gradient in immersed P4VP films, in which the extent of swelling is the highest on the surface and gradually decays with an increase in depth from the surface to the inner inside of the film.…”

“…30 Unlike surface wrinkling found on the surface of P4VP films, poly(2-vinylpyridine) (P2VP) films form craters after immersion in an aqueous solution consisting of high molar concentrations of HAuCl 4 . 10 The surface cratering involves three stages: nonuniform swelling, partially dewetting on the surface, and Marangoni flow-induced accumulation of solid solutes. The first two stages occur during film immersion, which produces blisters inside the film.…”

“…Several surface instabilities in thin films have received much attention due to their easy self-organization to generate well-tailored and diverse topological features. Several surface instabilities include dewetting, , blistering and cratering, − surface wrinkling, − and breath-figure self-assembly. − These surface instabilities occur differently. Dewetting is mainly determined by competing intermolecular and interfacial interactions for films supported on a solid substrate.…”

Frequency-Dependent Dewetting of Thin Liquid Films Using External ac Electric Field

“…The stability of the thin liquid films is crucial for all of these applications, as the rupture of the film leads to the failure of devices. Under certain conditions, dewetting is a dynamic process of retracting the liquid film from a surface due to the intermolecular forces and external perturbations such as electric field, temperature, etc. − Dewetting is often observed in various industrial and natural surfaces, such as coating and printing processes, lubrication, and droplet coalescence. , Hence, a fundamental study of the dewetting dynamics and its final morphology is necessary to use dewetting for potential applications.…”

“…6−16 Dewetting is often observed in various industrial and natural surfaces, such as coating and printing processes, lubrication, and droplet coalescence. 17,18 Hence, a fundamental study of the dewetting dynamics and its final morphology is necessary to use dewetting for potential applications.…”