CONTINUOUS-PHASE TRANSITIONS AND ORIENTATIONAL ORDERING IN MONOLAYERSOF ZWITTERIONIC AMPHIPHILIC MOLECULES AT FLUID INTERFACES

Experimental and theoretical evidence is presented which shows that or ientational ordering of highly polar head groups in monolayers of amph iphilic molecules (zwitterionic 2-amino-tetradecanoic acid) at fluid i nterfaces produces a smooth continuous phase transition. Hence this su pports the view that models which interpret the sharp 'kink' point pha se transitions exhibited by phospholipid monolayers at oil/water inter faces as being purely due to reorientation are deficient in important respects and suggests that the model which is most likely to be applic able to lipids of biological interest at oil/water interfaces is a ble nd of chain melting and collective molecular orientational ordering.