Disjoining Pressure Isotherms for Oil−Water−Oil Emulsion Films

Abstract

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 to 1500 Pa. Disjoining pressure isotherms are given for films stabilized by the nonionic surfactants n-dodecyl pentaoxyethylene glycol ether (C12E5) and n-decyl-β-d-glucopyranoside (C10-β-Glu) and the anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) in the presence of added electrolyte. For C12E5 and AOT, the emulsion films are indefinitely stable even for the highest concentration of NaCl tested (136.7 mM), whereas the C10-β-Glu film shows coalescence at this salt concentration. For film thicknesses greater than ∼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-stabilized emulsion droplets. For thin emulsion films (< 20 nm) certain systems showed isotherms that suggested the presence of an additional repulsive force with a range of ∼20 nm.

Electrostatic effects in films stabilised by non-ionic surfactants

“…Binks et al have measured the disjoining pressure of an emulsion film (oil/water/oil) made from a 0.5 mM solution of n-decyl-β-D-glucopyranoside (C 10 -β-Glu) without added salt [23]. The experimental data are still well fitted by the DLVO model with a Debye length κ −1 = 34.1 nm (corresponding to about 0.08 mM monovalent ions).…”

Forces between two oil drops in aqueous solution measured by AFM

“…Some research has been undertaken on the interaction between liquid interfaces using other techniques, notably the liquid surface force apparatus (LSFA) [1][2][3] and a novel approach using magnetic particles dispersed inside an emulsion droplet [4][5][6][7][8]. These techniques have their strengths and weaknesses.…”

Emulsions stability, from dilute to dense emulsions — Role of drops deformation

“…In particular surface and hydrodynamic properties between individual oil drops in solution can provide insight into stability and coalescence in liquid-liquid extraction. Among recent techniques on the measurement of the interactions between liquid interfaces, we quote as an example: (i) the liquid surface force apparatus using magnetic particles dispersed inside an emulsion droplet [148][149][150]-ii) the atomic force microscopy measurement [151][152][153] between a rigid probe and a liquidliquid interface and theoretical analyses to interpret the measurements in light of the interfacial deformation [154][155][156][157][158].…”