An investigation into the supramolecular structure of ternary gel systems using oscillatory rheometry, microscopy, and low frequency dielectric spectroscopy

A series of ternary gel systems based on cetostearyl alcohol (CSA) and ceto macrogol 1000 or sodium lauryl sulfate have been studied using oscillatory rheology, differential interference contrast (DIC) microscopy, cryoscanning electron microscopy (cryo-SEM), and low-frequency dielectric analysis in o rder to elucidate the nature of the lamellar structures formed in relation to composition. The effects of altering the concentration of CSA (0.25% to 8% w/w) for 1% and 2% w/v cetomacrogol 1000 and 0.5% and 1% w/v sodium laur yl sulfate systems have been investigated, with marked increases in the sto rage and loss moduli seen on increasing the concentration of CSA for both s urfactants. DIC microscopy indicated that at low CSA concentrations, needle like structures were seen which, on increasing the concentration, were obse rved to congregate into nuclei. At concentrations of 4% CSA and above, neos pherical structures were also observed. Cryo-SEM revealed that the needleli ke objects were sheet structures ascribed to lamellar gel phases, while the nuclei were folded "rosettes" formed by those sheets, with the spherical s tructures being ascribed to cetostearyl alcohol. It was also noted that the lamellae were more tightly folded at 8% w/w CSA, which may be associated w ith the higher rheological moduli for these systems. Low-frequency dielectr ic analysis was performed over a frequency range of 10(4) Hz to 10(-2) Hz. A decrease in both the dielectric loss and capacitance was observed as the concentration of cetostearyl alcohol was increased. The dielectric data wer e described in terms of an equivalent circuit model based on a modified Max well-Wagner response. A good correlation was found between the fitted and e xperimental data and the effect of altering the gel composition on specific features of the equivalent circuit are discussed.