Stability Properties of Surfactant-Free Thin Films at Different Ionic Strengths: Measurements and Modeling

Abstract

Foam lamellae are the smallest structural elements in foam. Such lamellae can experimentally be studied by analysis of thin liquid films in glass cells. These thin liquid films usually have to be stabilized against rupture by surface active substances, such as proteins or low molecular weight surfactants. However, horizontal thin liquid films of pure water with a radius of 100 μm also show remarkable stability when created in closed Sheludko cells. To understand thin film stability of surfactant-free films, the drainage behavior and rupture times of films of water and NaCl solutions were determined. The drainage was modeled with an extended Derjaguin-Landau-Verwey-Overbeek (DLVO) model, which combines DLVO and hydrophobic contributions. Good correspondence between experiment and theory is observed, when hydrophobic interactions are included, with fitted values for surface potential (ψ(0,water)) of -60 ± 5 mV, hydrophobic strength (B(hb,water)) of 0.22 ± 0.02 mJ/m(2), and a range of the hydrophobic interaction (λ(hb, water)) of 15 ± 1 nm in thin liquid films. In addition, Vrij's rupture criterion was successfully applied to model the stability regions and rupture times of the films. The films of pure water are stable over long time scales (hours) and drain to a final thickness >40 nm if the concentration of electrolytes is low (resistivity 18.2 MQ). With increasing amounts of ions (NaCl) the thin films drain to <40 nm thickness and the rupture stability of the films is reduced from hours to seconds.

Superstable Ultrathin Water Film Confined in a Hydrophilized Carbon Nanotube

“…The meniscus brings more water molecules closer together which interact and essentially balance the forces acting on the film. These films are one order of magnitude smaller than previous experimental observations 26…”

“…Moreover, we should consider the effect of confinement on the intermolecular interactions. The DLVO theory 26 assumes two infinite plane-parallel surfaces, where interactions exist only between water molecules (blue spheres) in the plane-surface, as indicated with white arrows in Figure 4 (b).…”

Wettability and Applications of Nanochannels

“…Interestingly, ultrathin water film of 3–20 nm remained stable inside the CNT nanochannels due to the molecular interactions of the water meniscus. The film thickness was smaller than the critical film thickness (≈40 nm) by 1 order of magnitude reported by the previous experimental results . In order to determine internal water wetting of CNT, Lindsay and co‐workers constructed a single‐walled CNT field‐effect transistor and used it as a nanofluidic channel that connected two fluid container, allowing determination of the electronic property of the single‐walled CNT when wetted by an analyte .…”

Self‐Sustaining 3D Thin Liquid Films in Ambient Environments

“…The importance of water thin films has been highlighted in the recent literature, but to date their creation has been difficult owing to the instabilities caused by high evaporation rates and high surface tension. [ 6,11,12 ] Instead, most studies of water TLFs require surfactants to reduce surface tension and use controlled humidity, temperature, and/or pressure environments to form and maintain a stable TLF. [ 2,6,11–18 ] Relatively few studies of water TLFs have been performed without additives, none of which have achieved film stability without carefully controlling the surrounding environment.…”

“…[ 6,11,12 ] Instead, most studies of water TLFs require surfactants to reduce surface tension and use controlled humidity, temperature, and/or pressure environments to form and maintain a stable TLF. [ 2,6,11–18 ] Relatively few studies of water TLFs have been performed without additives, none of which have achieved film stability without carefully controlling the surrounding environment. [ 11,12 ] Furthermore, as noted above nearly all reported wetting TLFs of water have planar geometries constructed following the methods pioneered by Scheludko and Platikanov over 50 years ago.…”