Self-Assembly of Double-Tail Anionic Surfactant Having Cyanobiphenyl Terminal Groups in Water

Abstract

This study reports the interfacial properties and lyotropic liquid crystal formation of sodium 1,2-bis{6-[4-(4-cyanophenyl)phenyloxy]hexyloxycarbonyl}ethanesulfonate (SBCPHS), which is a double-tail surfactant with cyanobiphenyl terminal groups, in water. Polarized microscopic observation of water/SBCPHS mixtures revealed the presence of columnar and lamellar phases. In the lamellar phase, myelin figures representing multilamellar tubes were observed, and some of these figures had a double-helix structure. In order to examine these liquid crystal structures in detail, the bilayer thickness of the lamellar tubes and the lattice parameters of the columnar phase were measured by small-angle X-ray scattering analysis. Four scattering peaks that could be ascribed to C2/m symmetry were observed for the columnar phase. The bilayer thickness and one of the lattice parameters were smaller than twice the molecular length of SBCPHS; this showed that the liquid crystal phases had intercalated structures. Comparison of SBCPHS with a typical double-tail hydrocarbon surfactant revealed that the cyanobiphenyl terminal groups in the former helped increase the stability of the liquid crystal formed at low temperatures. The stabilizing effect of the cyanobiphenyl terminal groups on the liquid crystals could have been driven by electrostatic intermolecular interactions between the terminal groups in antiparallel arrangement of the SBCPHS molecules.

Periodic Formation/Breakdown of Lamellar Aggregates with Anionic Cyanobiphenyl Surfactants

“…17−19 In comparison between these phase diagrams in Figure 4, lamella LCs tend to be stabilized against dilution by increasing the number of cyanobiphenyl mesogens in the molecules (N CB ), which started to appear from 10 wt % for 8F-B2ES (N CB = 0), 5 wt % for CB-B2ES (N CB = 1), and 1 wt % for SBCPHS (N CB = 2). The stabilization effect of N CB on lamellar LCs arises from the intermolecular cyanobiphenyl− cyanobiphenyl interactions in an antiparallel arrangement, 41,42 which will be one of driving forces for aggregation in bilayers, as seen in earlier papers.…”

“…These hybrid surfactants were synthesized and purified as described in SI-1 of the Supporting Information and a previous report . The symmetric double-tail surfactants SBCPHS (sodium 1,2-bis­{6-[4-(4-cyanophenyl)­phenyloxy]­hexyloxycarbonyl}­ethanesulfonate) and 8FS­(EO) 2 (sodium 1,2-bis­{1 H ,1 H ,2 H ,2 H -perfluorodecyloxycarbonyl}­ethanesulfonate) were synthesized in a previous study. − ,, The structures of the final products were elucidated by infrared (IR) spectroscopy (FTS-30, Bio-Rad Laboratories, Berkeley, CA) and proton nuclear magnetic resonance ( 1 H NMR) spectroscopy (JNM-GX270, JEOL, Tokyo, Japan). The purity of the final compounds was confirmed by elemental analysis (EA 1110, CE Instruments, Ltd., Wigan, U.K.) and normal-phase high-performance liquid chromatography (HPLC, SIL 150A-5 column, Intersil) with an ultraviolet (UV) detector (λ = 254 nm).…”

“…Similar to the use of fluorocarbon chains, a thermotropic mesogen can also help promote lyotropic LC formation and cause microsegregation from saturated hydrocarbon chains . In an earlier study, two surfactants sodium 1,2-bis­{6-[4-(4-cyanophenyl)­phenyloxy]­hexyloxycarbonyl}­ethanesulfonate (SBCPHS; Figure ) and sodium 1,2-bis­(tetradecyloxycarbonyl)­ethanesulfonate (SBTDS; Figure ) were synthesized to examine the effects of cyanobiphenyl (CB) terminal groups on the aqueous LC phase behavior. , Lamellar and columnar phases were formed in aqueous SBCPHS mixtures, and the temperature stability range for SBCPHS liquid crystals was wider than that for SBTDS. This clearly shows that LC phases can be stabilized by intermolecular interactions between the cyanobiphenyl terminal groups, when in the antiparallel arrangement of the SBCPHS molecules.…”