The influence of glycerol on the properties of neutral and ionically charged Lα-phases

The influence of glycerol on the stability and the viscoelastic properties of two aqueous Lα-phases (Lalpha phases) have been investigated. The first Lα-phases A was an uncharged Lα-phases from a 5 wt.% solution of nonionic surfactant C12-16E6 (a mixture of several ethoxylated carbon alcohols) and 240 mM of the co-surfactant ethylhexylglycerid (EHG). The second Lα-phases B had the same composition as Lα-phases A but was ionically charged by addition of 10 mM ionic surfactant sodium dodecyl sulfate (SDS). The Lα-phases A broke down when 40% (v/v) of the water was replaced by the solvent glycerol, while Lα-phases B remained stable until 80% of the water was replaced by glycerol. Contrary to Lα-phases A, Lα-phases B was highly viscoelastic with a yield stress value. The shear modulus was less dependent on the glycerol content. The shear modulus of the uncharged phase was much smaller than for Lα-phases B and decreased strongly with increasing glycerol content. The stability of the Lα-phases decreased also strongly with temperature. Small-angle X-ray scattering (SAXS) measurements showed that the interlamellar spacing of the Lα-phases B increased with increasing glycerol content. It is argued that the decrease of the shear modulus and the increase of the interlamellar spacing with glycerol make the interaction potential between the bilayers softer. Consequently, the interlamellar distance between the bilayers fluctuates stronger and the spacing becomes longer.