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MODULATED PHASES IN AMPHIPHILIC MONOLAYERS AT THE WATER/AIR INTERFACE
 

Summary: MODULATED PHASES IN AMPHIPHILIC MONOLAYERS
AT THE WATER/AIR INTERFACE
David Andelman
Raymond and Beverly Sackler Faculty of Exact Sciences, School of Physics and Astronomy,
Tel Aviv University, Ramat-Aviv 69978, Tel Aviv, Israel
ABSTRACT
Recently, modulated phases of insoluble monolayers of fatty acids and phospholipids
spread on the water/air interface have been observed by fluorescence microscopy experi-
ments. We propose a theoretical explanation of this observation by including electrostatic
(dipolar) interactions in the total free energy calculation for the monolayer. Dipoles can
originate from two sources: neutral amphiphiles have a permanent dipole and charged am-
phiphiles have an induced one. Modulated phases are found to be stable in two different
limits: close to the liquid-gas transition and at low temperatures. Several phases with
stripe and hexagonal symmetry are predicted and the phase transitions between them are
calculated.
INTRODUCTION
Most of the research on insoluble amphiphilic monolayers at the water/air inter-
face [1-2] has been conducted either on fatty acids such as pentadecanoic, myristic, oleic,
arachidic and stearic acids, or on phospholipids such as DPPC and DPMA. Insoluble
monolayers (so-called Langmuir monolayers) have been studied using several experimental

  

Source: Andelman, David - School of Physics and Astronomy, Tel Aviv University

 

Collections: Materials Science; Physics