The Formation and Collapse of Mixed Monolayers of 1-Hexadecanol and 1-Octadecanol with Interest in Evaporation Control of Water by Monolayers

Abstract

Abstract Collapse pressure, equilibrium spreading pressure, and melting points of binary mixtures of hexadecanol and octadecanol were measured in order to study the phase equilibrium among a monolayer, a solid, and a liquid and to apply the result to evaporation control of water by monolayers. Collapse pressure and equilibrium spreading pressure of solid mixtures have a maximum at a given composition, while the equilibrium spreading pressure of a liquid mixture has not a maximum. Melting points have a minimum at a given composition. From thermodynamic analysis of these phase equilibriums, it was concluded that the mixed monolayer and liquid mixture were ideal solutions, while the solid mixture was a lattice-distorted solid solution. That is, when the two components of different molecular volumes form a solid solution, the solid solution has high energy due to the distortion of the crystal lattice and consequently, it becomes easier to spread and the mixed monolayer becomes more stable against collapse. From these results, the relations between the composition of solid solution and the surface pressure, composition, and specific evaporation resistance of the mixed monolayer in equilibrium with the solid solution, were obtained.