Effect of binding state between hydrophilic and hydrophobic portions on aggregation structure of monolayer

The effect of molecular structure of anionic (2CnPOH (n=12, 16)) amphiphiles with dialkyl chains that bind with the hydrophilic group only through ether bond and cationic (2CnN+2C (n=18, 22)) amphiphiles with dialkyl chains that directly bind with the hydrophilic group without a spacer on aggregation structure of amphiphile monolayers was investigated on the basis of π-A isotherm measurement and electron diffraction (ED) analysis. π-A Isotherms of the 2C12POH and 2C18N+2C monolayers exhibited a plateau region, whereas those of the 2C16POH and 2C22N+2C monolayers did a sharp rise in surface pressure with decreasing surface area. ED analysis revealed that 2C12POH, 2C18N+2C and 2C22N+2C monolayers were in an amorphous state even at higher surface pressures. On the other hand, the 2C16POH monolayer was in a crystalline hexagonal state in which the degree of molecular aggregation is low. Noncrystallization of the 2C12POH, 2C18N+2C and 2C22N+2C monolayers and the low degree of molecular aggregation of the 2C16POH monolayer may be attributed to the molecular aggregation by distantness between dialkyl chains in their parallel alignment due to binding between the hydrophilic and hydrophobic portions without or through only one spacer.