engleski

Formation of the Lamellar Phase of Alkyl-benzenesulphonates from Electrolyte/Water/n-Octanol Solutions

The behaviour of mesophases in the ternary system of sodium 1’-(4)-dodecylbenzenesulphonate (4SDBS)/water/Mg(NO3)2 was determined by using crossed polarizers, polarized light microscopy (LM), and light microscopy with differential interference contrast (DIC). In comparison to the binary system without Mg(NO3)2, these systems showed changes in the formation of phases. A shift of the biphasic region boundary, i.e., of the isotropic + lamellar phase region, towards lower concentration of surfactant has been found. In the biphasic region, a growth of the lamellar microtubuli from the viscous isotropic phase into cylinders, and afterwards, their distortion into cones, has been observed as a homogeneous nucleation, if the samples have been kept between microscopic object and cover glass at room temperature. A transition of the lamellar phase to an inverse hexagonal one has been observed in water and n-octanol mixtures above 20% of the octanol content, due to the corresponding convex / concave change of the lamellar surface curvature. The effect is caused by increasing the concentration of a non-polar solvent. The dynamics of the formation of lamellar phases followed in the aqueous solutions of simple-, or double tailed ABS showed that the nucleation of lamellar phases undergoes the following process: the association of surfactant molecules into micelles, transition either of flat lamellar to bent lamellar bilayers forming cylinders, or bending of flat lamellar into focal conic structure, and finally the formation of secondary aggregates, i.e., into lamellar spherulites.

Lamellar Phase; Alkyl-benzenesulphonates

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