It is well known that hydrophobic substances aggregate strongly in aqueous solution due to the hydrophobic attraction between such substances. The strength and long effective distance of the hydrophobic attraction has fascinated researchers since it was first measured directly. However, its origin is still in the heat of an argument despite numerous efforts have been devoted to disclose it, and no critical theory still cannot successfully explain its unusual long-range effectiveness. This review introduces a series of investigations on the hydrophobic attraction by direct measurements using atomic force microscopy (AFM), and provides a current overview of the origin and mechanisms of this attractive force.

Microcapsules whose shell part consists of polymer gel undergoes unique changes in its volume when the core material changes in its solubility; this volume change is a similar function observed for stimuli-responsive properties of smart hydrogels.