Effect of the Spacer Length on the Solid Phase Transitions of Dissymmetric Gemini Surfactants

Abstract

Three dissymmetric gemini surfactants (abbreviated as 12-s-14) in which n-dodecyldimethylammonium bromide and n-tetradecyldimethylammonium bromide are connected at the polar headgroups 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 the 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 smectic type. The number of thermal phase transitions and the sequence of phases are markedly affected by the spacer length; that is, they depend on the configuration of the two alkyl chains with respect to the spacer.

Synthesis and thermotropic liquid crystalline properties of heterogemini surfactants containing a quaternary ammonium and a hydroxyl group

“…1 shows good reproducible behavior of all the compounds investigated over multiple heating and cooling cycles. This indicates the thermal stability of C m OhpNC n is obviously higher than that of the bis(quaternary ammonium) Gemini surfactants as reported in the references [3][4][5][6], the latter decomposed on the second heating. Fig.…”

“…Recently, the growing interest in the thermotropic liquid crystal behavior of amphiphiles has been extended to a new family of Gemini surfactants, characterized by two conventional surfactant molecules whose polar headgroups are connected by a spacer. So far, however, only bis(quaternary ammonium) Gemini surfactants have been investigated for their thermotropic phase transition, for instance, 15-s-15 having a variable length of alkylene spacer [3], m-2-m fixing two methylene groups as the spacer with the length of the alkyl tails changing (m = 12, 14, 16 and 18) [4], 12-s-14 with dissymmetric lengths of alkyl tails and different s (s = 2, 6 and 10) [5], and 12-EO x -12 with an oligo(oxyethylene) spacer chain [6]. Although these Gemini surfactants could form thermotropic liquid crystals, the mesophases were thermal unstable.…”

Synthesis and aqueous solution properties of homologous gemini surfactants with different head groups

“…However, new classes of gemini surfactants have emerged and have attractive attention: dissymmetric gemini surfactants with hydrocarbon chains of different length and with two identical head groups [21][22][23][24][25][26][27][28] and asymmetric ones with two identical hydrocarbon chains and two different hydrophilic head groups [29][30][31][32][33][34]. The research on asymmetric gemini surfactant was less documented.…”

Rapid synthesis of Gemini surfactants using a novel 915-MHz microwave apparatus

“…The yields decreased at reaction temperatures above 160 . The decomposition temperature of cationic gemini surfactants is around 200 11 .…”