PHASE BEHAVIOUR OF L62 AND P104 IN WATER AND BENZYL ALCOHOL MIXTURES AND PHYSICO-CHEMICAL PROPERTIES OF L62, P104 and BRIJ-78 AQUEOUS SOLUTIONS

Abstract

The isothermal ternary phase and aggregation behaviour of amphiphilic co-polymer-water-benzyl alcohol systems was investigated for the two non-ionic surfactant systems: L-62 and P104 at 25 C. The phase boundaries were examined and identified by visual inspection under polarized light to check for phase separation, homogeneity and birefringency. The microstructures in the lyotropic liquid crystalline phases were determined and characterized by small-angle X-ray scattering (SAXS). Also, Physico-chemical properties of aqueous solutions of Brij-78 [polyoxyethylene (20) Stearly ether (C18H37(OCH2CH2)nOH)] and tri-block copolymers L-62 ((EO)6(PO)34(EO)6) and P104 ((EO)27(PO)61(EO)27) non-ionic surfactants were studied. The micellar behaviour of the three surfactants in aqueous media was investigated at 25 C. Other thermodynamic and solution properties of aqueous mixtures of the surfactants were investigated with cloud point, conductometric and viscometric techniques. Effects of inorganic salts (NaCl, Na2SO4 and AlCl3), ionic surfactants (SDS and CTAB) and nonionic surfactant (TX-114) on the three physico-chemical properties of the surfactant solutions were also determined. A variety of lyotropic liquid crystalline (LLC) phases are thermodynamically stable in the two systems. In the P104-water-benzyl alcohol ternary system, four lyotropic liquid crystalline phases were found to be thermodynamically stable while in the L62-water-benzyl alcohol ternary system, one lyotropic liquid crystalline phase was found to be stable. The copolymer is completely soluble in benzyl alcohol. Cloud point of pure surfactant solutions decreased with increase in surfactant concentrations and inorganic salts: NaCl, Na2SO4 and AlCl3 depress cloud points. Ionic surfactants, SDS and CTAB, both raised the cloud point of the three nonionic surfactants to above 100 0C but TX-114, a nonionic surfactant, lowered cloud point of all three nonionic surfactants. Both specific conductivity and relative viscosity increased slightly with increase in surfactant concentration in all cases. Benzyl alcohol does not produce most lyotropic liquid crystals especially reverse phases and therefore not recommended in cases where such phases are needed.