engleski

Effect of the spacer length on the solid phase transitions of dissymmetric gemini surfactants

Three dissymmetric gemini surfactants (abbreviated as 12-s-14) in which n- dodecyldimethylammonium bromide and n- tetradecyldimethylammonium bromide are connected at the polar head groups by a flexible -(CH2)s- spacer (s = 2, 6, or 10) have been synthesized. The influence of the spacer length on the structural and thermal properties of 12-s-14 surfactants was investigated by means of IR and NMR spectral analysis, X-ray diffraction, thermogravimetry, differential scanning calorimetry and polarizing optical microscopy. Geminis with s = 2 or 10 form monolayers in which two alkyl chains are in the trans configuration, while gemini with s = 6 forms interdigitated bilayers with two alkyl chains in the cis configuration with respect to the spacer. All compounds exhibited a complex polymorphism and thermotropic mesomorphism from the stable crystalline form to the liquid crystalline phases of the smectic type. Number of thermal phase transitions and sequence of phases are markedly affected by the spacer length ; i.e., they depend on the configuration of two alkyl chains with respect to the spacer.

gemini surfactants ; phase transition ; thermal properties

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