Mixed monolayer studies of 12-hydroxyoctadecanoic acid and its esters |
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Authors: | Hirosi Matuo D K Rice D M Balthasar D A Cadenhead |
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Institution: | Department of Chemistry, State University of New York at Buffalo, Buffalo, New York 14214, U.S.A. |
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Abstract: | Mixed monolayers of two bipolar/bipolar systems have been studied and the results are compared with those obtained from similar monopolar/monopolar systems. DL-12-Hydroxyoctadecanoic acid, methyl DL-12-hydroxyoctadecanoate, and ethyl DL-12-hydroxyoctadecanoate were used as the bipolar substances in this paper. The surface pressure-area/molecule isotherms of both the DL-12-hydroxyoctadecanoic acid/methyl DL-12-hydroxyoctadecanoate system and the methyl DL-12-hydroxyoctadecanoate/ethyl DL-12-hydroxyoctadecanoate system were measured at a variety of compositions and temperatures. Taking advantage of the thermodynamic threatment which has been formulated by Motomura, the two-dimensional phase diagrams and the apparent molar entrophy, enthalpy and energy changes were evaluated for both systems. The DL-12-hydroxyoctadecanoic acid/ethyl DL-12-hydroxyoctadecanoate system exhibited a deformed cigar type diagram while the methyl DL-12-hydroxyoctadecanoate/ethyl DL-12-hydroxoctadecanoate system formed a normal cigar type diagram. The transition thermodynamic quantities of both the DL-12-hydroxyoctadecanoic acid/ethyl DL-12-hydroxoctadecanoate system and the methyl DL-12-hydroxyoctadecanoate/ethyl DL-12-hydroxyoctadecanoate system were respectively much larger than those of similar monopolar/monopolar systems: hexadecanoic acid/ethyl hexadecanoate and ethyl hexadecanoate/ethyl heptadecanoate. |
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Keywords: | mixed monolayers bipolar substances two-dimensional phase diagram DL-12-hydroxyoctadecanoic acid |
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