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

Abstract

The influence of glycerol on the stability and the viscoelastic properties of two aqueous L α-phases (Lalpha phases) have been investigated. The first L α-phases A was an uncharged L α-phases from a 5 wt.% solution of nonionic surfactant C 12–16E 6 (a mixture of several ethoxylated carbon alcohols) and 240 mM of the co-surfactant ethylhexylglycerid (EHG). The second L α-phases B had the same composition as L α-phases A but was ionically charged by addition of 10 mM ionic surfactant sodium dodecyl sulfate (SDS). The L α-phases A broke down when 40% (v/v) of the water was replaced by the solvent glycerol, while L α-phases B remained stable until 80% of the water was replaced by glycerol. Contrary to L α-phases A, L α-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 L α-phases B and decreased strongly with increasing glycerol content. The stability of the L α-phases decreased also strongly with temperature. Small-angle X-ray scattering (SAXS) measurements showed that the interlamellar spacing of the L α-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.