The effect of poly(propylene glycol) on the formation of lyotropic liquid crystalline phases of amphiphiles containing glycerol head groups

In order to prepare a nonlamellar lyotropic liquid crystalline structure, amphiphiles (PPG-Gly 340 and 1000) containing poly(propylene glycol)s of different molecular weights, 340 and 1000 respectively, as hydrophobic chains and glycerol as head groups were synthesized and investigated by optical microscopy and small angle X-ray scattering. The effect of poly(propylene glycol) on the developments of reverse bicontinuous cubic phase (V2) and reverse hexagonal phase (H2) was examined by the mixing of PPG-Gly with glyceryl monooleate (GMO). The addition of PPG-Gly to GMO expedites the lamellar-Ia3d (V2)-Pn3m (V2) transformation of the hydrated GMO. Poly(propylene glycol)s of different chain lengths show rather different effects on both the phase behavior and the dimension of the structure. The Pn3m lattice parameter can be reduced by more than 20% on the addition of PPG-Gly1000. In contrast, the addition of PPG-Gly 340 increases the dimension by less than 5%. This result is explained by the hydrophobic chain splay. From polarizing optical microscopy, the addition of PPG-Gly 1000 to GMO enhances the formation of H2 phase substantially. The appearance of the H2 phase lasts for a temperature range of ca. 23 °C. It was also found that the H2 phase coexists with the Pn3m phase and does not disappear at the same temperature, indicating a distribution of compositions of the hydrated PPG-Gly 1000/GMO mixtures.