Structural-Size Control of Domain from Nano to Micro: Logical Balancing between Attractive and Repulsive Interactions in Two Dimensions

Molecules aggregate to form a structure through various interactions involving dispersion force, electrostatic force, and so on. In two-dimensional systems, a surface energetic effect is further important for the molecular aggregation structure. We show that the domain size and its morphology in the mixed monomolecular film composed of hydrocarbon and fluorocarbon skeletons with different surface free energies extremely change depending on pH and NaCl concentration in the subphase. Such morphological changes can be interpreted by the balance of dipole density and line tension, which help in the development of an understanding of phase separation phenomena and provide a novel technique for structural control in two dimensions.