Self-assembling Structures and Sol-Gel Transition of Optically Active and Racemic 12-Hydroxystearic Acids in Organic Solvents
Self-assembling structures and sol-gel transition in solution of optically active and racemic 12-Hydroxystearic acids (HSA) have been investigated by means of small-angle X-ray scattering (SAXS), differential scanning calorimetry and rheological measurements. Apparently two kinds of gel, transparent gel and turbid gel were obtained in different solvents or by changing concentrations in the same solvent. The melting temperature of the turbid gel is higher than that of the transparent gel. The difference can be qualitatively explained by the dissolution of the crystals (melting point depression) in non-ideal solutions. The SAXS profiles of the transparent gel composed of fibrillar structures have a similar shape at different concentrations, although the intensity is larger for the gels with higher concentrations of 12-HSA. The SAXS analysis reveals that the cross-section of fibrils have square or circular shape (no anisotropic shape) with the radius of gyration 83 Å. On the other hand, for the turbid gel structural inhomnogeneity becomes significant with concentration. The gelation properties and the structures are found to be similar in the racemic HSA gel and the optically active (D-HSA) gel.
KeywordsSelf-assembling structures Sol-gel transition Low-molecular weight gelator Small-angle X-ray scattering
H. T. acknowledges Prof. T. Hashimoto for his valuable comments.
References and Notes
- 7.Newman S, Krigbaum WR, Carpenter KK (1956) J. Phys. Chem. 58:968Google Scholar
- 8.Hildebrand JH, Scott RL (1950): The solubility of Nonelectrolytes 3rd ed Dover Publications, New YorkGoogle Scholar
- 11.In order to experimentally estimate the effect of dispersion of the crystals, we measured the melting temperature of the sample prepared by freeze-drying of 7wt% D,L-12-HSA gel in benzene, i.e., the structures are expected to be frozen in the dispersed state. As a consequence, the melting temperature was 79.4 °C, which is by 1.2 °C lower than that of the bulk crystal. Therefore, the effect of the dispersion of the crystal in the gel state is expected to be smallGoogle Scholar
- 12.Polymer HandBook, third edGoogle Scholar
- 13.Van Kreveren (1972): Properties of Polymers, Elsevier Publishing Company, AmsterdamGoogle Scholar
- 19.Mittelbach, Porod G (1961) Acta Phys Austriaca, 14:185Google Scholar