Soft materials based on colloidal self-assembly in ionic liquids

Ionic liquids (ILs) have attracted much attention as dispersion media for colloidal systems as alternatives to organic solvents and electrolyte solutions. Although colloidal stability is an essential factor for determining the properties and performance of colloidal systems containing ILs, detailed mechanisms for colloidal stabilization have not yet been studied. In the first part of this paper, we highlight our fundamental studies on colloidal stability. Three different repulsive forces, electrostatic, solvation, and steric interactions, are examined for their effectiveness in stabilizing colloidal particles in ILs. In the second part of this report, we provide an overview of our recent studies on colloidal soft materials in the presence of ILs. On the basis of the suspended state of the silica colloid particles, two different soft materials, a colloidal gel and a colloidal glass, were prepared in ILs. Their functional properties, including ionic transport, rheological, and optical properties, are discussed in relation to the microstructures of the colloidal materials.