Isothermal Switching of Phases in Lyotropic Liquid Crystalline Surfactant Systems via Photoreactions of Solubilized Molecules

Abstract

Light induced phase transitions were found in lyotropic liquid crystalline systems of aqueous cetyltrimethylammonium bromide (CTAB) and of Aerosol-OT(AOT)/decane/water: the isothermal transitions isotropic --t nematic and isotropic + hexagonal in CTAB systems were triggered by the photocyclization of a solubilized naphthyl vinyl ether, the transition isotropic + inverse-hexagonal in the ternary AOT system was induced by the trans-cis photoisomerization of a solubilized stilbazolium salt. The transition time (between starting irradiations and detecting anisotropic phases) was found to increase with the difference between irradiation temperature and transition temperature in the non irradiated case; transition times were shorter by two orders of magnitude in the AOT-system as compared to CTAB. The position of isotropic/liquid crystalline phase borders produced by partial irradiation of layers of aqueous CTAB were more stable in hexagonal as compared to nematic systems.

Interactions of AOT Lyotropic Liquid Crystals and Photochemical Reactions of Hydroxystilbazolium Bromides: Steering Reactions and Switching Phases

“…Sodium bis(2-ethylhexyl)sulfosuccinate (aerosol OT, AOT ) was purchased from Fluka (>99%). 1-Methyl-4-[2-(4-hydroxyphenyl)-vinyl]-pyridinium bromide (HSB) was prepared as described previously, 1- n -pentyl-4-[2-(4-hydroxyphenyl)-vinyl]-pyridinium bromide (C5-HSB) and 1- n -hexadecyl-4-[2-(4-hydroxyphenyl)-vinyl]-pyridinium bromide (C16-HSB) were prepared analogously. C5-HSB: mp 230−234 °C dec; 1 H NMR (DMSO) δ/ppm = 0.9 (t, 3H, pentyl CH 3 ), 1.3 (m, 4H, pentyl CH 2 ), 1.9 (m, 2H, pentyl CH 2 ), 4.5 (t, 2H, NCH 2 ), 6.9 (d, 3 J = 8 Hz, 2H, aromatic H), 7.3 (d, 3 J = 16.8 Hz, 1H, olefinic H), 7.65 (d, 3 J = 8 Hz, 2H, aromatic H), 8.0 (d, 3 J = 16.8 Hz, 1H, olefinic H), 8.2 (d, 3 J = 6.7 Hz, 2H, aromatic H), 8.9 (d, 3 J = 6.7 Hz, 2H, aromatic H), 10.2 (s, 1H, OH).…”

“…In various lyotropic liquid crystalline (LLC) surfactant systems phase transitions can be triggered via photoreactions of certain solubilized aromatic compounds, as recently reviewed . Among the surfactant systems investigated there were aqueous cationic ones (cetyltrimethylammonium bromide), aqueous anionic ones (potassium myristate), and ternary systems composed of water, decane, and sodium bis(2-ethylhexyl)sulfosuccinate (AOT) . In these systems several photochemically reactive aromatic compounds were shown to influence phase transition temperatures in a specific way when solubilized at low concentrations.…”

Changes in self-assemblies induced by temperature concentration and light

“…Such aggregation change implies the transition from a highly organized structure, with at least one (lamellar), two (hexagonal and rectangular) or three (cubic) dimensional translational order, into a much simpler isotropic (micellar) phase with no directional order. (125)(126)(127)(128)(129)(130). Different kinds of phase transitions have been achieved, for example, from micellar isotropic to hexagonal (126)(127)(128)(129), nematic (127)(128)(129)(130)(131), inverse hexagonal (125,127), and lamellar phases (125,130).…”