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KMID : 0604519970230020071
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Journal of the Society of Cosmetic Scientists of Korea
1997 Volume.23 No. 2 p.71 ~ p.96
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Dishoining Pressure Isotherms for oil-water-oil Emulsion Films
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Abstract
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We have used a novel liquid surface forces apparatus(LSFA) to determine the variation of disjoining pressure with film thickness for dodecane-water-dodecane emulsion films. The LSFA allows measurement of film thicknesses in the range 5-100 nm and disjoining pressure from 0-1500 Pa. Disjoining pressure isotherms are given for films stabilised by the nonionic surfactants n-dodecyl pentaoxyethylene glycol ether(C_(12)E_(5) and n-decyl-O-D-glucopyranoside(C_(10)-β-Glu) and the anionic surfactant sodium bis(2-ethylhexyl) sulphosuccinate(AOT) in the presence of added electrolyte. For (C_(12)E_(5) and AOT, the emulsion films are indefinitely stable even for the highest concentration of NaCl tested (136.7 mM) whereas the C_(10)-β-Glu film shows coalescence at this salt concentration. For film thicknesses greater than approximately 20 nm with all three surfactants, the disjoining pressure isotherms are reasonably well described in terms of electrostatic and van der Waals, forces. For the nonionic surfactant emulsion films, the charge properties of the monolayers are qualitatively similar to those seen for foam films. For AOT emulsion films, the monolayer surface potentials estimated by fitting the isotherms are similar to the values of the zeta potential measured for AOT stabilised emulsion droplets. For thin emusion films(<20nm) certain systems showed isotherms which suggested the presence of additional repulsive force with a range of approximately 20nm.
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