title: Adhesion of oil to kaolinite in water.
abstract: Uniform coats of kaolinite particles on a flat glass substrate were prepared to be sufficiently smooth and thin to allow reliable measurement of contact angles of captive crude oil drops in a range of salt solutions, without any particle removal. The contact angle hysteresis was used to infer the extent of oil adhesion via rupture of the intervening water film and anchoring of charged groups to kaolinite. For sodium chloride solutions, adhesion decreases monotonically with pH and/or salinity, with strong adhesion only manifested under acidic conditions with salinity at most 0.1 M. Calcium chloride solutions at pH around 6 switch from strong adhesion in the range 0.001-0.01 M to weak adhesion at higher concentrations. For all mixtures of sodium and calcium chlorides investigated, a total ionic strength above 0.1 M guarantees a weak adhesion of oil to kaolinite. Results are qualitatively consistent with theoretical expectations of electrostatic interactions, with H(+) and Ca(2+) being potential-determining ions for both interfaces.
authors.affiliation: Department of Applied Mathematics, Research School of Physics and Engineering, Australian National University, Canberra ACT 0200, Australia.
authors.forename: Evgenia V
authors.initials: EV
authors.lastname: Lebedeva
authors.forename: Andrew
authors.initials: A
authors.lastname: Fogden
mesh_terms: D052918:Environmental Restoration and Remediation / Q000379:methods*; D005618:Fresh Water / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D007616:Kaolin / Q000737:chemistry*; D009994:Osmolar Concentration; D010578:Petroleum / Q000032:analysis*; D012965:Sodium Chloride / Q000737:chemistry; D013499:Surface Properties; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry*
chemical_list: D010578:Petroleum; D014874:Water Pollutants, Chemical; D007616:Kaolin; D012965:Sodium Chloride