Surface conductivity and disjoining pressure of common black films stabilized with sodium dodecyl sulfate

Journal Article · Wed Jul 01 04:00:00 EDT 1998 · Journal of Colloid and Interface Science

DOI:https://doi.org/10.1006/jcis.1998.5520· OSTI ID:653276

Swayne, E N; Newman, J; Radke, C J ^[1]

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1. Lawrence Berkeley National Lab., CA (United States). Earth Science Div.

The authors have conducted simultaneous measurements of the disjoining pressure and the film conductance for sodium dodecyl sulfate- (SDS-) stabilized foam films in aqueous electrolyte solutions and over a range of film thicknesses. The disjoining pressure ascertains the repulsive forces within the film while the conductance gauges the possible changes in mobilities and concentrations of the ions within the thin-film region, relative to their bulk values. The disjoining pressure is measured using a modified version of the porous-glass-plate technique. To permit electrical measurements in the same apparatus, a novel film holder was designed in which the film is formed in the annular region between two concentric, porous stainless steel disks. The inner and outer disks serve as electrodes, and they constrain the current to flow radially through the film. To avoid electroosmosis, the film conductance is obtained using AC impedance spectroscopy. New data are reported for the disjoining pressure, conductance, and film thickness of 0.002-M SDS foam films with and without added sodium nitrate. Film conductances exhibit a decrease with decreasing film thickness, which suggests a decrease in the mobility of the film ions relative to their bulk values, even for films as thick as 40 nm. Surface-charge densities are estimated from the conductance data and are consistent with available surface tension data. However, the surface-charge densities estimated from the disjoining-pressure data are more than an order of magnitude smaller than the values estimated from conductance and surface-tension data. Improvements in both experimental precision and theory are needed to overcome this discrepancy.

• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: AC03-76SF00098
• OSTI ID: 653276
• Journal Information: Journal of Colloid and Interface Science, Journal Name: Journal of Colloid and Interface Science Journal Issue: 1 Vol. 203; ISSN 0021-9797; ISSN JCISA5
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
IONIC CONDUCTIVITY
PRESSURE MEASUREMENT
SOAPS
SURFACE POTENTIAL
SURFACTANTS
THIN FILMS