Do hydration forces play a role in thin film drainage and rupture observed in electrolyte solutions?

The mechanism that controls bubble coalescence in electrolyte solutions remains unresolved. The problem is difficult as sensitive dynamic thin film processes are critical. Here we discuss the relationship between film dynamics, specific-ion effects and the combining rules that codify electrolyte effects on bubble coalescence. The relationship with Hofmeister effects is explored, revealing that these very different manifestations of specific ion effects ultimately have the same origin, being the interfacial positioning of ions, which for the air–water interface correlates with the empirically derived α and β assignments used in the combining rules. Ion hydration is important as it strongly influences the interfacial positioning of ions and therefore ultimately bubble coalescence, however dynamic events determine if a collision results in coalescence and therefore we conclude that hydration forces play no role in bubble coalescence in electrolyte solutions.

Do hydration forces play a role in thin film drainage and rupture observed in electrolyte solutions?Figure optionsDownload high-quality image (251 K)Download as PowerPoint slideHighlights
► The physical meaning of the α and β assignments is described.
► Combining rules arise from bubble coalescence dynamics.
► Specific ion effects in bubble coalescence and Hofmeister are related.
► Hydration forces do not play a role in bubble coalescence in electrolyte solutions.
► Hydration does play a role by influencing the location of ions within the interface.