Phase behavior of surfactant mixtures and the effect of alkyl chain and temperature on lyotropic liquid crystal

Abstract In order to study lyotropic liquid crystal (LLC) which have good stability to strong electrolytes, inorganic salts and pH, the mixtures of Polyoxyethylene-10-oleyl ether (Brij 97) with different Polyoxyethylene (20) sorbitol fatty acid ester (Tweens®) were studied. Firstly, the phase diagrams had been constructed for Brij 97/Tween 20/H2O (Tween 20 system), Brij 97/Tween 40/H2O (Tween 40 system), Brij 97/Tween 60/H2O (Tween 60 system) and Brij 97/Tween 80/H2O (Tween 80 system). It showed that the difference in the alkyl chain length and insaturation of Tweens® had significant effect on the lyotropic liquid crystal phase region size. Secondly, the system containing Tweens® had smaller viscous moduli (G”), elastic moduli (G') and larger lattice parameter (α) than the system without Tweens®, which indicated that the latter has higher stability than the former. It is worth noting that the sample (Brij 97/Tween 40/H2O = 52.5/10/37.5) appeared as a mixed phase of hexagonal phase (H1) and micellar cubic phase (I1) at 37 °C, while the other samples behaved as hexagonal phase. It should also be noted that with the increase in temperature, the rheological properties of sample (Brij 97/Tween 60/H2O = 0/55/45) showed changes from viscous dominated to elastic dominated to viscous dominated, which provided a basis for thermosensitive materials and drug carriers.