Abstract
Choline carboxylates (ChCm with m = 12-18) are simple biocompatible anionic surfactants with very low Krafft temps., possessing a rich aq. phase behavior. In the present work, we have investigated the thermotropic mesomorphism of anhyd. ChCm salts for m = 12-18. Transition temps. and enthalpies detd. by differential scanning calorimetry reveal that all investigated compds. exhibit three ...
Abstract
Choline carboxylates (ChCm with m = 12-18) are simple biocompatible anionic surfactants with very low Krafft temps., possessing a rich aq. phase behavior. In the present work, we have investigated the thermotropic mesomorphism of anhyd. ChCm salts for m = 12-18. Transition temps. and enthalpies detd. by differential scanning calorimetry reveal that all investigated compds. exhibit three different phases between -20 and 95 °C. The phases were further characterized by optical polarizing microscopy, NMR spin-spin relaxation, and X-ray scattering measurements. The nature of the phases was identified with increasing temp. as cryst., semicryst., and liq.-cryst. lamellar. Even long-chain choline carboxylates (m = 18) were found to melt into a lamellar liq.-cryst. phase below 100 °C. Accordingly, with choline as counterion in simple fatty acid soaps, not only the water soly. is considerably enhanced but also the m.ps. are substantially reduced, hence facilitating thermotropic mesomorphism at temps. between 35 and 95 °C. Thus, simple choline soaps with m = 12-18 may be classified as ionic liqs.
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