Rheological behaviours of the hexagonal and lamellar phases of glucopone (APG) surfactant

Abstract

The rheological behaviours of hexagonal and lamellar liquid crystalline phases of glucopone–water–hydrocarbon systems were investigated. Four different types of hydrocarbon namely heptane, octane, dodecane and tetradecane were considered. Small-angle X-ray scattering (SAXS) and optical polarizing microscopy were used for phase identification and structure characterization. The SAXS data was further analyzed in terms of lattice parameters and area per surfactant head group. The area head group of the hexagonal phases seemed not to depend on the alkane chain length. On the other hand, the area head group for the lamellar phases was found to increase as the alkane chain is lengthened. The frequency-dependent storage and loss modulus were found to exhibit characteristics of the hexagonal and lamellar phases in the linear viscoelastic regions. The elastic properties of hexagonal phases were also found to be unaffected when higher homologue of the alkane series was considered, while for lamellar phases the elastic properties were found to decrease. The effects of temperature on the rheological behaviours of hexagonal and lamellar phases were also investigated and their melting transition temperatures were found to be almost similar. Moreover, the melting transition temperatures determined by rheology differ only slight from that determined by microscopy. The rheological quantities were found to decrease when the temperature was increased. In general, the effects of different types of hydrocarbon in the rheological behaviours were found to be more profound in the lamellar than in the hexagonal phases.