Structure of liquid-crystalline phases formed by sodium dodecyl sulphate and water as determined by optical microscopy, X-ray diffraction and nuclear magnetic resonance spectroscopy

Abstract

The lyotropic liquid crystals formed in the sodium dodecyl sulphate + water system have been studied using optical microscopy, low-angle X-ray diffraction and nuclear magnetic resonance spectroscopy. Optical microscopy reveals the presence of a mesophase at compositions between those of the hexagonal and lamellar phases. The magnitudes of water and sodium n.m.r. quadrupole splittings indicate that this phase contains rod micelles similar to those in the hexagonal phase, despite the fact that the material aligns at glass surfaces with the director normal to the surface. The X-ray measurements suggest that the phase has a deformed hexagonal structure and results from a gradual distortion of the hexagonal lattice with increasing surfactant concentration. An hypothesis to account for its formation and properties is proposed, involving hydrogen-bonded water links between micelles.

Magnesium and calcium surfactants Ternary phase diagrams of magnesium and calcium dodecylsulphate with decanol and water

“…Comparison of A2H values in the D phases of these systems is made difficult because of difficulties in preparing samples with identical compositions. However, it appears that A2H values differ by a few percent for samples having almost identical compositions in the order Ca (50~ > Mg (40 ~ > Be (30 ~ -Na (30 ~ Previously, it has been shown [20][21] that A2H values in the liquid crystalline phases of alkali alkylsulphates increase slightly (10-15 %) with increasing temperature in this range. The slight differences in A2H values between different systems is consequently attributed mainly to differences in experimental temperature.…”

Infrared and Raman spectra of alkali palmityl sulfates

“…The absence of splitting of the CH, rocking mode makes it unlikely that the two bands in the CH, scissoring region belong to the same mode and deuteration of the a-CH, group in sodium and lithium palmitate have led to an unambigous assignment of the 1479 cm-' band to the a-CH, scissoring mode. In fact, a band at 1479 & 1 cm-I is observed in practically all alkali Can 3. Raman spectra of polycrystalline n-hexadecanol and of lithium, sodium (type I1 and type III), potassium, rubidium, ammonium, and cesium palmityl sulfate in the 1000-1500 cm-' region.…”

Chromonic liquid crystals formed by CI Acid Red 266 and related structures

“…Water ( 2 H 2 O) splitting is in the range observed for ionic surfactant hexagonal phases. [22,23] But, remarkably, the behaviour is very simple as shown in Table 5. Two of the dyes have Δ 23 Na obs values of 10-12 kHz, the third is 4 kHz.…”

“…This is the behaviour observed for anionic surfactants where Δ 23 Na obs values of 10-12 kHz are frequently observed for hexagonal phases, independently of composition. [22,23] The explanation is that ion binding is governed by the Manning ion condensation model. [24,25] Counter-ions condense on highly charged surfaces until most of the charges are balanced, whatever the composition.…”