| Abstract
| - The role of electrostatic interaction in the domain morphology of amide, ether, ester, and amine monoglycerolmonolayers (abbreviated as ADD, ETD, ESD, and AMD, respectively) with systematic variation in themolecular structure of the headgroup region is investigated. Experimental studies using Brewster anglemicroscopy (BAM) and grazing incidence X-ray diffraction (GIXD) show that the characteristic features ofthe condensed monolayer phase, such as domain morphology, crystallinity, and lattice parameters, are verydifferent for these monoglycerols. Therefore, the intermolecular interactions of the four amphiphilicmonoglycerols are investigated in detail. First, the dipole moments of four monoglycerols of similar structurebut with different functional groups are calculated by a semiempirical quantum mechanical technique. Thedipole moments for monoglycerols follow the sequence AMD < ETD < ESD < ADD for the population ofconformers of compounds investigated. The dipolar repulsion energies for the amphiphilic monoglycerolsare also calculated for different possible mutual orientations between the dipoles. The calculated dipolarenergies also follow the same trend for different possible headgroup orientations. These results can explainthe domain shape of the monoglycerols observed experimentally. Second, ab initio calculations on the basisof the HF/6-31G** method are performed for representative monoglycerol headgroup segments. The resultsshow that the intermolecular interaction energy related to dimer formation follows the order ETD < ESD <AMD < ADD segments, similar to that observed in experiment except in the case of the AMD segment. Therelative importance of intra- and intermolecular hydrogen bonding in dimers is analyzed. The enhanced roleof the intermolecular interaction relative to intramolecular interaction in the case of AMD contributes to therelatively high intermolecular interaction energy for the particular conformation of the dimer of AMD segmentas observed from ab initio calculation. The present work shows that the variations in headgroup molecularstructure alter drastically the domain shape, and the theoretical calculations conclusively reveal the importantrole of the electrostatic interactions for the mesoscopic domain architecture.
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