Surface forces: Changing concepts and complexity with dissolved gas, bubbles, salt and heat

•Severe limitations in the DLVO theory of colloid stability are discussed.•Ion specificities and the Hofmeister series are considered in surface forces.•The effects of dissolved gases on surface forces are examined.•Recent work using the interaction of hot bubbles with solutes is presented.

A number of missing factors influence surface forces strongly; so much so that the classical theory is often irrelevant to the real world. Among these factors, dissolved atmospheric gas or other sparsely soluble solutes play a central role in long range hydrophobic forces. Bubble-bubble interactions exhibit unexplained non-Hofmeister ion specificity. Inhomogeneity in temperature between bubbles and solvent can be used to catalyse high temperature reactions at low temperatures.Further, the additivity of electrostatic and dispersion forces assumed in DLVO theory is inadmissible. It also neglects ion specificity (Hofmeister effects) due to dispersion forces acting on ions.An account is given of these complexities that are missing from classical theories of surface forces. It is shown how these phenomena can be exploited for a range of novel technologies.

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