Surfactant binding by polyelectrolyte gels and its application to electro-driven chemomechanics

Surfactant binding and molecular assembly reactions of solvated and weakly cross-linked polyelectrolytes having charges on the side chain and on the backbone have been studied using various kinds of oppositely charged surfactants. We have found that there are three categories of surfactant binding: they are cooperative and stoichiometric, non-cooperative and stoichiometric, and cooperative and non-stoichiometric. The modes of these categories are predominantly determined by the steric chemical structure of the surfactant, hydrophobicity and charge densities of the polyelectrolytes. The mechanism of complex formation and the structure formation are discussed. A water-swollen polymer gel which swings and undulates water backwards was made by applying an electric field and making a reversible assembly-reaction of surfactant on the gel. Using this principle, a fish-like soft-machine was made which slowly moves forwards by undulating its tail. The motion is analysed and the mechanism is discussed.