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

Abstract

A series of ternary gel systems based on cetostearyl alcohol (CSA) and cetomacrogol 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 order 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 lauryl sulfate systems have been investigated, with marked increases in the storage and loss moduli seen on increasing the concentration of CSA for both surfactants. DIC microscopy indicated that at low CSA concentrations, needlelike structures were seen which, on increasing the concentration, were observed to congregate into nuclei. At concentrations of 4% CSA and above, neospherical structures were also observed. Cryo-SEM revealed that the needlelike objects were sheet structures ascribed to lamellar gel phases, while the nuclei were folded "rosettes" formed by those sheets, with the spherical structures 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 with the higher rheological moduli for these systems. Low-frequency dielectric 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 were described in terms of an equivalent circuit model based on a modified Maxwell-Wagner response. A good correlation was found between the fitted and experimental data and the effect of altering the gel composition on specific features of the equivalent circuit are discussed.

Drug Molecules as Probes for Studying the Compatibility Between Gels and Mucous Tissue with Dielectric Spectroscopy

“…From the current response, the complex impedance or permittivity of the sample is obtained which can be related to properties determined by the charges moving in the system. Pharmaceutical applications of this technique include the analysis of disperse systems such as liquid emulsions, [3][4][5][6] semisolid creams, 7,8 liposomes, 9-11 micellar systems, [12][13][14] and liquid crystalline structures. [15][16][17] Furthermore, a number of publications on the dielectric response of gels have appeared.…”

Investigating the influence of excipient batch variation on the structure, consistency and physical stability of polysorbate 60–based topical vehicles

“…Hence, more hydrophilic gel phase forms in batch 1 ternary system. To get a deeper insight into these gel systems, it is worth trying to perform additional techniques such as synchrotron X-ray investigations [37], low-frequency dielectric analysis and cryo-scanning electron microscopy [38] so as to clarify the nature of the lamellar structures formed. With reference to X-ray scattering data, the swelling ability of polysorbate 60 : cetostearyl alcohol mixed emulsifying wax (molar ratio, 1:20) when dispersed in water was obviously demonstrated (Figures 11 and 12).…”