Separation of chiral phases by compression: kinetic localization of the enantiomers in a monolayer of racemic amphiphiles viewed as mixing cholesteric liquid crystals

A monolayer of amphiphiles is studied as a film of cholesteric liquid crystal (ChLC) mixed by the left- and right-handed chiral enantiomers. The equilibrium equations for the chiral phase separation (CPS) order parameter and molecular orientation pattern are derived by minimizing the free energy of the mixing ChLC. We found a one-dimensional (1D) periodic localization of the enantiomers, a stripe-type of CPS. By incorporating the free energy of the stripe-CPS into the thermodynamic calculation, we show that its pressure–area isotherms behave like a spatial 2D van der Waals equation of state and must have a pressure-plateau region for the phase transition from racemic phase to CPS. This gives a clear explanation of the CPS in a racemic monolayer.