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

The effect of molecular structure of anionic (2C(n)POH (n = 12, 16)) amphip hiles with dialkyl chains that bind with the hydrophilic group only through ether bond and cationic (2C(n)N(+)2C (n = 18, 22)) amphiphiles with dialky l chains that directly bind with the hydrophilic group without a spacer on aggregation structure of amphiphile monolayers was investigated on the basi s of pi-A isotherm measurement and electron diffraction (ED) analysis. pi-A Isotherms of the 2C(12)POH and 2C(18)N(+)2C monolayers exhibited a plateau region, whereas those of the 2C(16)POH and 2C(22)N(+)2C monolayers did a s harp rise in surface pressure with decreasing surface area. ED analysis rev ealed that 2C(12)POH, 2C(18)N(+)2C and 2C(22)N(+)2C monolayers were in an a morphous state even at higher surface pressures. On the other hand, the 2C( 16)POH monolayer was in a crystalline hexagonal state in which the degree o f molecular aggregation is low. Noncrystallization of the 2C(12)POH, 2C(18) N(+)2C and 2C(22)N(+)2C monolayers and the low degree of molecular aggregat ion of the 2C(16)POH monolayer may be attributed to the molecular aggregati on by distantness between dialkyl chains in their parallel alignment due to binding between the hydrophilic and hydrophobic portions without or throug h only one spacer. (C) 2000 Elsevier Science B.V. All rights reserved.