Effect of silicone oil on the microstructure, gelation and rheological properties of sorbitan monostearate–sesame oil oleogels

Oleogels contain oil or a non-polar liquid which is gelled with an agent called an organogelator. The aim of this study was to evaluate the effects of the addition of silicone oil (cyclopentasiloxane) to the gelation process and to the properties of sorbitan monostearate (SMS)–sesame oil oleogel and compared with that of SMS–sesame oil oleogel and SMS–cyclopentasiloxane oleogel. Three different oil phases; sesame oil phase, cyclopentasiloxane phase and a mixture of cyclopentasiloxane and sesame oil, were used to prepare oleogels with SMS gelator. The critical gelling concentrations (CGC) for oleogels were determined using different concentration of SMS in a range of 5%–22% (w/w). The characterization of the developed oleogels was done using Fourier transform infrared spectroscopy (FTIR), polarized light microscope, rheometer, X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The addition of cyclopentasiloxane reduced the CGC of SMS–sesame oil oleogel from 20% to 10% (w/w). In microscopic characterization, the oleogels with a mixture of oil phases showed the longer and thicker three-dimensional gel network than that of oleogels with sesame oil and cyclopentasiloxane. FTIR studies demonstrated that this network formation was mainly due to hydrogen bonding. Rheological measurements revealed that the combination of cyclopentasiloxane and sesame oil produced strong gel with higher complex modulus values and longer linear viscoelastic region than oleogels prepared with sesame oil and cyclopentasiloxane. In addition, oleogels with the combination of the two oils had higher enthalpy (ΔHm) and entropy (ΔSm) thus could increase thermodynamic stability of the oleogels. Therefore, the addition of cyclopentasiloxane can improve the physical, thermal properties and stability of SMS–sesame oil oleogel, provide greater sensory profile and better product aesthetics. The developed oleogel can be a novel carrier for topical drug delivery. Keywords: Oleogel, Microstructure, Rheology, Sesame oil, Silicone oil, Sorbitan monostearat