Pentacosanoyl-10:12-diynoic acids

Ultra-Thin Films of Tricosanoyl and Pentacosanoyl-10 12-Diynoic Acids... 

ULTRA-THIN FILMS OF TRICOSANOYL AND PENTACOSANOYL-10 12-DIYNOIC ACIDS AND THE RESULTANT POLYMERS... 

Surface pressure/Area per molecule isotherms are reported for tricosanoyl and pentacosanoyl-10 12-diynoic acids over the complete temperature range from completely condensed to completely expanded. Approximate heats for the expanded/ condensed, disorder/order transition are reported. These data permitted the selection of temperatures at which expanded and partially or fully condensed films could be polymerized at the air/water interface in situ) or after being transferred onto glass substrates. 

While increasing chain length, often with dicationic aqueous substrates, can help promote a condensed state that facilitates polymerization, similar effects can be achieved by lowering the temperature. It is, however, very important to define the temperature ranges where expanded or condensed or both states may exist. In addition, consideration of film stability, in so far as it is significant in achieving a polymerized state, should be taken into account. In this paper, we present temperature dependent studies of the physical states of films of two simple diacetylenic fatty acids, tricosanoyl and pentacosanoyl-10 12-diynoic acids. We also report the results of spectral studies of polymerized films under carefully defined conditions of the shorter chain acid, both at the air/water interface and on glass substrates. 

Tricosanoyl-10 12-diynoic acid was obtained from Allied Corporation and was recrystallized from hexane and stored in darkness below 0°C prior to dilution. Pentacosanoyl-10 12-diynoic acid was obtained from Dr. Dennis Chapman of the Royal Free Hospital, London, England, and was used without further purification and stored in darkness below 0°C prior to dilution. 

Surface pressure (jt) vs. area per molecule (A) isotherms for tricosanoyl-10 12-diynoic add (TCDA) and pentacosanoyl-10 12-diynoic acid (PCDA) obtained at a compressional rate of 6 A /molecule min, are shown in figures 1 and 2, respectively. 

Figure 3. The onset of the liquid expanded/liquid condensed transition (t ) as a function of the temperature for tricosanoyl-10 12-diynoic acid (TCDA) and pentacosanoyl-10 12-diynolc acid (PCOA). Since only two Isotherms In each case exhibited a phase transition a linear extrapolation to zero pressure was used to obtain values of Tg (the lowest temperature at which an expanded phase could exist). Previous experience indicates a linear extrapolation is a reasonable approximation and that any non-linearity would result in lowering the Tg values in Table 1 by no more than a fraction of a degree.

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