M. K. Nagarajan, Jitendra Shah
Mar 1, 1981
Citations
0
Influential Citations
14
Citations
Journal
Journal of Colloid and Interface Science
Abstract
Surface pressure-specific area isotherms for 12-d-hydroxyoctadecanoic (I), 12-ketooctadecanoic (II), 12-d-hydroxy-9-trans-octadecenoic (III), and 12-d-hydroxy-9-cis-octadecenoic (IV) acids and their methyl esters were determined at the airwater interface at 303.15°K. The data indicate that the introduction of a hydrophilic functional group near the middle of the hydrophobic alkyl chain part of both saturated and unsaturated C18 fatty acids causes (i) greater film expansion (more so in compounds I, II, and III than in IV) vis-a-vis corresponding unsubstituted monopolar carboxylic acids, and (ii) the formation of highly compressible intermediate transition monolayer states. The results are explained on the basis of the existence of four monolayer molecular conformations of the C18 bipolar fatty acidsesters, viz., flat, bent, bowed, and vertical. It is further shown that the rotational isomeric states (viz., anti, gauche, eclipsed) of the methylenic group located at the 12th carbon position are also important in determining the monolayer behavior of the cis and trans geometric isomers of unsaturated 12-d-hydroxy-9-octadecenoic acidsesters. The monolayer behavior of the corresponding methyl esters roughly parallels that of their parent acids.