| Abstract
| - Thermoreversible organogels were prepared from carbamates with alkyl side chains of different lengths.Gelation was possible only up to an alkyl side chain length of 12 carbons, beyond which crystallizationoccurs, due to the dominant van der Waals interaction between the alkyl chains. This is in contrast to otheralkane-based organogels, in which gelating efficiency increased with the length of the alkane chain (seeAbdallah, D. J.; Weiss, R. G. Adv. Mater. 2000, 12, 1237). The critical concentration for gelation decreasesdrastically with an increase in the side chain length. Xerogels of these show birefringent fibers withuniform cross section and unlimited growth in one direction. The extent of this unlimited growth is affectedby the length of the alkyl side chain in the carbamate, which finally ceases the gel formation ability ofthe carbamate. Cryogenic scanning electron microscopy images of the gels are similar to those of xerogels.From X-ray diffraction of the fibers, we propose that the growth direction is along the plane of hydrogenbonds between the carbamate molecules. The thickness of the fibers depends on the length of the alkylside chain. Morphological differences are seen between gels prepared by slow cooling and quenching ofthe solution. Thus, the morphology of the fibrous xerogels of the carbamates can be tailored for specificapplications, by the choice of the alkyl side chain length and the rate of cooling the solution.
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