Surface Forces and Deformation at the Oil−Water Interface Probed Using AFM Force Measurement

Abstract

The immobilization of droplets of a hydrocarbon liquid (n-decane) on a flat solid surface has allowed the forces of interaction between a silica colloidal particle and the hydrocarbon−water interface to be measured using the atomic force microscope. Results are presented which demonstrate that nonpolar surfaces prepared in this way acquire a significantly negative diffuse layer potential in electrolyte solutions, as indicated by force distance relationships which obey DLVO theory at large separations. At smaller separations, deviations from DLVO theory are observed, followed by an attractive force which causes the instantaneous engulfment of the silica particle by the droplet. The presence of trace quantities of the anionic surfactant sodium dodecyl sulfate (SDS) radically alters the forces between the two surfaces, creating a significant barrier to engulfment, and an apparent “softening” of the fluid interface.

Force measurements with the atomic force microscope: Technique, interpretation and applications

“…Therefore an electrostatic repulsion is observed when interacting with a silica particle. As expected from DLVO theory this repulsion decays roughly exponentially with a decay length equal to the Debye length [875].…”

Interaction forces between oil–water particle interfaces—Non-DLVO forces

“…This is consistent with previous results on non-polar liquids where jumpin is not always observed at low ionic strengths. 8,18 At all higher concentrations of sodium perchlorate and all cases for calcium nitrate the force curves all terminate in jump-in.…”

“…These later techniques include total internal reflection microscopy, a modified surface forces apparatus, 2,3 alignment of droplets in magnetic fields 4,5 and atomic force microscopy (AFM). [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] All of these measurements are motivated by the study of how the structure of the molecules at liquid interfaces mediates the interaction forces between liquid-liquid or liquid-vapor interfaces. Understanding the interaction forces between liquid interfaces leads to insight into the properties of complex fluids commonly encountered in industrial applications.…”

Probing Mechanical Properties of Water–Crude Oil Interfaces and Colloidal Interactions of Petroleum Emulsions Using Atomic Force Microscopy

“…For systems involving a deformable interface, zero separation distance becomes more difficult to determine due to the coupling effect of interfacial deformation and cantilever bending upon applied force. [25][26][27][28][29][30] Adsorbed interfacial species can greatly influence interaction forces and also govern the degree of droplet deformation under applied load, with the latter greatly influenced by interfacial rigidity. 31 In the absence of hydrodynamic effects, droplet deformation results from the interaction forces exceeding the Laplace pressure.…”