Chiral phase separation of a monolayer domain comprised of racemic mixture of chiral phospholipids due to the electrostatic energy

Domain shape transition of racemic dipalmitoylphosphatidylcholine (DPPC) monolayers indicates the possibility of chiral phase separation in a racemic domain. We have analyzed the chiral phase separation in a racemic domain taking into account the surface pressure, line tension, electrostatic energy due to the spontaneous polarization and electric quadrupole density, and mixing entropy to clarify the mechanism of shape transition of racemic monolayer domains. We derive the condition of the chiral phase separation in an analogous form to the Bragg–Williams theory, and predict that chiral phase separation occurs as the spontaneous polarization in monolayer normal increases in agreement with our experimental results. The electric quadrupole density plays an important role in the chiral phase separation of a racemic monolayer domain.