Simultaneous measurement of dynamic force and spatial thin film thickness between deformable and solid surfaces by integrated thin liquid film force apparatus

Abstract

Interactions involving deformable surfaces reveal a number of distinguishing physicochemical characteristics that do not exist in interactions between rigid solid surfaces. A unique fully custom-designed instrument, referred to as integrated thin liquid film force apparatus (ITLFFA), was developed to study the interactions between one deformable and one solid surface in liquid. Incorporating a bimorph force sensor with interferometry, this device allows for the simultaneous measurement of the time-dependent interaction force and the corresponding spatiotemporal film thickness of the intervening liquid film. The ITLFFA possesses the specific feature of conducting measurement under a wide range of hydrodynamic conditions, with a displacement velocity of deformable surfaces ranging from 2 μm s to 50 mm s. Equipped with a high speed camera, the results of a bubble interacting with hydrophilic and partially hydrophobic surfaces in aqueous solutions indicated that ITLFFA can provide information on interaction forces and thin liquid film drainage dynamics not only in a stable film but also in films of the quick rupture process. The weak interaction force was extracted from a measured film profile. Because of its well-characterized experimental conditions, ITLFFA permits the accurate and quantitative comparison/validation between measured and calculated interaction forces and temporal film profiles.

Probing surface interactions of underwater oleophobic polyelectrolyte multilayers

“…5, and the EDL interaction between droplet and PEMs coated substrate is calculated using Eq. (6) according to the literature (Zhang et al 2016b), where k B is the Boltzmann constant, T is the absolute temperature, ρ ∞ is the number density of ions in the aqueous solution, z is the valency of the ion, e is the electron charge, ψ d and ψ s are the surface potentials of the droplet and PEMs substrate, respectively, and κ −1 is the Debye length that can be calculated using Eq. 7, The overall interaction force between droplet and the substrate is the integral of the hydrodynamic pressure and disjoining pressure based on the Derjaguin approximation,…”

Mimicking coalescence using a pressure-controlled dynamic thin film balance

“…Earlier studies related to film retraction that involved direct film visualisation by interferometry have focused on supported films formed between a deformable interface and a solid surface. [40][41][42] However, the behaviour of supported films has been found to be remarkably different compared to free-standing ones, i.e. those studied by the thin film balance technique or those formed between two droplets/bubbles.…”

Interfacial properties pertinent to W/O and O/W emulsion systems prepared using polyaromatic compounds

“…Studying interfacial dilatational rheology is a powerful tool to probe the adsorption and association of surface active molecules at oil-water interfaces, providing a better understanding of the microscopic properties of an interfacial film [21]. The stability of thin liquid films between two liquid droplets is reported to be critical for emulsion stability [22] while the coalescence time characterizes the stability of this thin liquid film [23,24].…”