engleski

Thermal Phase Transitions of Cationic Oligomeric Surfactants

A series of cationic oligomeric surfactants (quaternary dodecyldimethylammonium ions with two, three or four alkyl chains connected with ethylene spacer at the headgroup level) were synthesized and characterized. The influence of the number of dodecyl chains, i.e. the degree of oligomerization on the structural and thermal properties of oligomeric surfactants was investigated by means of IR and NMR spectral analysis, X-ray diffraction, thermogravimetry, differential scanning calorimetry, and polarizing microscopy. The number of thermal phase transitions and the sequence of phases are markedly affected by the degree of oligomerization. Dimeric and trimeric surfactant exhibited a complex polymorphism and thermotropic mesomorphism from the crystalline form to the liquid crystalline phases of smectic type. In contrast, tetrameric surfactant displayed only one endothermic transition associated with melting and decomposition. The observed effects are explained by different chain packing in the solid phase.

oligomeric surfactants; solid phase transitions

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