title: Forces between hydrophobic solids in concentrated aqueous salt solution.
abstract: Much research has focused on the discovery and description of long-ranged forces between hydrophobic solids immersed in water. Here we show that the force between high contact-angle solids in concentrated salt solution (1 M KCl) agrees very well with van der Waals forces calculated from Lifshitz theory for separations greater than 5 nm. The hydrophobic solids are octadecyltrichlorosilane-coated glass, with an advancing contact angle of 108°. Thus, in 1 M salt solution, it is unnecessary to invoke the presence of a hydrophobic force at separations greater than 5 nm. Through measurement in salt solution, we avoid the necessity of accounting for large electrostatic forces that frequently occur in pure water and may obscure resolution of other forces.
authors.affiliation: Department of Chemical Engineering, Virginia Tech, Blacksburg, Virginia 24060, USA.
authors.forename: Dean J
authors.initials: DJ
authors.lastname: Mastropietro
authors.forename: William A
authors.initials: WA
authors.lastname: Ducker
mesh_terms: D005898:Glass / Q000737:chemistry; D057927:Hydrophobic and Hydrophilic Interactions; D008956:Models, Chemical; D011189:Potassium Chloride / Q000737:chemistry*; D012821:Silanes / Q000737:chemistry*; D012996:Solutions / Q000737:chemistry; D055672:Static Electricity; D013816:Thermodynamics; D014867:Water / Q000737:chemistry*
chemical_list: D012821:Silanes; D012996:Solutions; D014867:Water; C061189:octadecyltrichlorosilane; D011189:Potassium Chloride