New SFA Techniques for Studying Surface Forces and Thin Film Patterns Induced by Electric Fields

Abstract

We describe two ways to measure normal and/or lateral forces between two surfaces in a surface forces apparatus (SFA) while an electric field is applied between the surfaces. The first method involves depositing thin conductive layers on the exposed substrate (usually mica) sheets; the second involves using the optically reflecting silver layers on the back surfaces of the sheets as the electrodes. Two types of experiments were performed using these new techniques: (1) measuring the effects of an electric field on the rheology of an approximately 40-microm-thick film of zeolite particles suspended in silicone oil and (2) a dynamic study of electric field-induced pattern formation of a thin polymer film. In the first study, under an electric field of strength approximately 106 V/m the shear force or effective viscosity of the colloid suspension was found to be two orders of magnitude higher than in the absence of the field, when the expected bulk value was measured. In the dynamic study, the initially uniform film transformed into a 2-D honeycombed network of depressed cells bounded by elevated ridges that grew slowly with time in a way consistent with previously derived theories. The new techniques should be applicable to studies of other systems and interactions, such as double-layer forces, micro- and nanoelectrorheology, electric field-induced ordering of particles, and the effects of electric fields on adhesion, friction, and lubrication.

The Effect of Water and Confinement on Self-Assembly of Imidazolium Based Ionic Liquids at Mica Interfaces

“…In contrast to our AFM experiments, this results in a fully equilibrated system with constant water concentrations. Two apposing mica (same quality as AFM experiment) surfaces were used in a 3-layer interferometer setup to perform the experiment 37 38 . Prior to every experiment, the SFA chamber was first purged by dried Ar gas ~30 min to remove residual humidity.…”

Adhesion and Surface Interactions of a Self‐Healing Polymer with Multiple Hydrogen‐Bonding Groups

“…An SFA was used to investigate the adhesion and contact mechanics of the polymer films under different conditions. Details of the SFA experimental setup have been reported previously . A top‐view optical microscope was coupled with the SFA, as reported previously, to observe the surface patterns associated with the adhesion and detachment of the polymer films.…”

Interactions of particulate matter and pulmonary surfactant: Implications for human health

“…SFA have been widely applied for quantifying a variety of forces in both biological [ 148 ] and non-biological systems [ 153 ], such as van der Waals forces, electrical double forces, hydrophobic interaction [ 154 ] and solvation forces (e.g., hydration interaction). The interfacial forces between different surfactant components have been directly quantified using an SFA [ 155 ].…”