Nanobubbles, pristine emulsions, high ionic strength electrokinetics -- paradoxes of Colloid and Interface Science

Abstract

There are three paradoxes in the modern Colloid and Interface Science supported by large bulk of experimental evidence and contradicting classical theoretical models: - Electrokinetics at high ionic strength; - Nanobubbles having life span on scale of days and weeks without any surface stabilization; - Pristine emulsions having life span on scale of days and weeks without any surface stabilization. We overview many dozens of experimental papers by broad spectrum of scientific groups from many countries. We consider this vast experimental data as unambiguous evidence that these phenomena exist. On other hand, classical theoretical models deny such possibility. This contradiction between experiment and theory justifies introduction of new theoretical models. We overview these models. It turns out that there is one common feature between most promising of them -- assumption regarding structured water layer at hydrophobic interface. That is why we combine these three phenomena in this review. There is extensive literature on century old idea of the structured water layer, experimental and theoretical. We overview this literature, which provides convincing support to this hypothesis. We discuss existing theoretical models that incorporate the structured interfacial water layer for the successful explanation of these phenomena in more detail. Theoretical model of electrokinetics at high ionic strength was developed several decades ago. Theoretical model explaining paradoxical longevity of nanobubbles and pristine emulsions by interaction between structured water layer and electric double layer is more recent.