Naslov
Polymorphism and Mesomorphism of Oligomeric Surfactants: Effect of the Degree of Oligomerization

Autori
Jurašin, Darija ; Pustak, Anđela ; Habuš, Ivan ; Šmit, Ivan ; Filipović-Vinceković, Nada

Izvornik
Langmuir (0743-7463) 27 (2011), 23; 14118-14130

Vrsta, podvrsta i kategorija rada
Radovi u časopisima, članak, znanstveni

Ključne riječi
oligomeric surfactants; degree of oligomerization; polymorphism; mesomorphism

Sažetak
A series of cationic oligomeric surfactants (quaternary dodecyldimethylammonium ions with two, three or four chains connected by an ethylene spacer at the head group level, abbreviated as dimer, trimer and tetramer) were synthesized and characterized. Influence of the degree of oligomerization on their polymorphic and mesomorphic properties was investigated by means of X-ray diffraction, polarizing optical microscopy, thermogravimetry and differential scanning calorimetry. All compounds display layered arrangements with interdigitated dodecyl chains. Increase in the degree of oligomerization increases the interlayer distance and decreases ordering in the solid phase ; while the dimer sample is fully crystalline with well-developed three dimensional ordering, the trimer and tetramer crystalize as highly ordered crystal smectic phases. The number of thermal phase transitions and sequence of phases are markedly affected by the number of dodecyl chains. Anhydrous samples exhibit polymorphism and thermotropic mesomorphism of smectic type, with the exception of the tetramer which displays only transitions at higher temperature associated with decomposition and melting. All hydrated compounds form lyotropic mesophases showing reversible phase transitions upon heating and cooling. The sequence of liquid crystalline phases for the dimer, typical of concentrated ionic surfactant systems, comprises a hexagonal phase at lower and a smectic phase at higher temperatures. In contrast, the trimer and tetramer reveal textures of the hexagonal phase.

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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