Abstract
It is well-established that oil-in-water creams can be stabilised through the formation of lamellar liquid crystal structures in the continuous phase, achieved by adding (emulsifier) mixtures comprising surfactant(s) combined (of necessity) with one or more co-surfactants. There is little molecular-level understanding, however, of how the microstructure of a cream is modulated by changes in co-surfactant and of the ramifications of such changes on cream properties. We investigate here the molecular architectures of oil-free, ternary formulations of water and emulsifiers comprising sodium dodecyl sulfate and one or both of the co-surfactants hexadecanol and octadecanol, using microscopy, small-angle and wide-angle X-ray scattering and small-angle neutron scattering. We then deploy these techniques to determine how the structures of the systems change when liquid paraffin oil is added to convert them to creams, and establish how the structure, rheology, and stability of the creams is modified by changing the co-surfactant. The ternary systems and their corresponding creams are shown to contain co-surfactant lamellae that are subtly different and exhibit different thermotropic behaviours. The lamellae within the creams and the layers surrounding their oil droplets are shown to vary with co-surfactant chain length. Those containing a single fatty alcohol co-surfactant are found to contain crystallites, and by comparison with the cream containing both alcohols suffer adverse changes in their rheology and stability.
Highlights
Lamellar lyotropic liquid crystals have gathered much interest over the years as they form the highly structured continuous phases of semi-solid oil-in-water (o/w) emulsions that are present in pharmaceutical and cosmetic skincare formulations and found across a range of processed foodstuffs and in veterinary preparations [1,2]
During the manufacture of creams, at high temperatures and at a high emulsifier concentration—beyond that needed to form an interfacial film at the oil droplet/water interface—the amphiphilic emulsifier molecules interact with the continuous phase and self-assemble as bilayers separated by regions of interlamellar water, thereby forming a lamellar liquid crystal phase [4,6]
In the research reported here, we explored systems prepared with emulsifiers comprising sodium dodecyl sulfate (SDS) combined with one or both of the fatty alcohols hexadecanol, and octadecanol
Summary
Lamellar lyotropic liquid crystals have gathered much interest over the years as they form the highly structured continuous phases of semi-solid oil-in-water (o/w) emulsions that are present in pharmaceutical and cosmetic skincare formulations and found across a range of processed foodstuffs and in veterinary preparations [1,2]. [3,12] we successfully revealed the microstructure of a system comprising water, liquid paraffin oil, sodium dodecyl sulfate (SDS) surfactant and an equimolar mixture of hexadecanol and octadecanol as co-surfactants In both the aqueous creams and their corresponding oil-free ternary systems, we found that an excess of emulsifier (10% w/w) gave rise to a lamellar gel network phase. In the studies reported here, we extend our investigations on model creams [3,12], investigating formulations based around the UK licensed, British Pharmacopoeial product, Aqueous Cream B.P. In keeping with Eccleston’s studies [11,16], we explore the consequences of changing the added co-surfactant on the molecular structure, rheology and stability of the creams and their corresponding ternary systems and elucidate the role of the co-surfactant alcohols in the gel network formation. Pharmaceutics 2020, 12, 864 and polarised light microscopy together with rheology measurements, and these were related to the structures of the creams and their corresponding ternary systems which were determined at the nanoscale using small-angle and wide-angle X-ray scattering (SAXS and WAXS, respectively) and small-angle neutron scattering (SANS)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
