Eutectic transformation in mixed monolayers of long normal chain fatty acids with 12-hydroxyoctadecanoic acid
✍ Scribed by Hirosi Matuo; Terumasa Mitsui; Kinsi Motomura; Ryohei Matuura
- Publisher
- Elsevier Science
- Year
- 1981
- Tongue
- English
- Weight
- 529 KB
- Volume
- 29
- Category
- Article
- ISSN
- 0009-3084
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✦ Synopsis
Surface pressure of mixed monolayers composed of fatty acids and DL-12-hydroxyoctadecanoic acid (12HOA) was measured at various compositions and temperatures. Two-dimensional phase diagrams were constructed. Tridecanoic acid (C~)-I2HOA, tetradecanoic acid (C~,)-12HOA, pentadecanoic acid (C~ s)-I 2HOA, hexadecanoic acid (C 16)-12HOA, and octadecanoic acid (C~8)-12HOA systems showed eutectic transformations in mixed monolayers. Surface pressure of eutectic point decreased with increase in the carbon numbers of fatty acid. The mole fraction of 12HOA at the eutectic point increased with increase in the carbon numbers. However, eicosanoic acid (C20)-12HOA and docosanoic acid (C22)-12HOA systems were not of eutectic type; they were immiscible with each other in the mixed monolayer. Apparent molar entropy and energy changes of CI4-12HOA and C~s-12HOA systems were evaluated by previously mentioned thermodynamic treatment. The entropy and energy changes of C~4 and Cls decreased slightly and steeply with increase in the mole fraction of 12HOA, x~, respectively. The values of 12HOA increased gradually with increase in x~.
Keywords."
mixed monolayer; two-dimensional phase diagram; eutectic transformation; 12hydroxyoctadecanoic acid.
*List of symbols: a c, mean molar area of condensed monolayer; a e, mean molar area of expanded monolayer; ff~,c, apparent partial molar area of component i in condensed monolayer; g]r,e, apparent partial molar area of component i in expanded monolayer; Aa 3', apparent molar area change;p, atmospheric pressure; R, gas constant;~ 'c apparent partia_l molar entropy of component i in condensed monolayer; ~7 'e apparent partial molar entropy of component i in expanded monolayer;As~, apparent molar entropy change of component i; T, absolute temperature; AU~, apparent molar energy change of component i; AV "r, apparent molar volume change; x~ r, mole fraction of component i in monolayer; x~ ,c, mole fraction of component i in condensed monolayer; x~ ,e, mole fraction of component i in expanded monolayer. Greek: ~,o, surface tension of water; 3 ,eq, surface tension at equilibrium state (which corresponds to the surface tension at the break point of the 7r-A curve); It, surface pressure; ~r °q, equilibrium surface pressure (which corresponds to the surface pressure at the break point of the 7r-A curve).