Research Summary
Emollient oils are ubiquitous ingredients in personal care products, especially in skin care and hair care formulations. They offer excellent spreading properties and provide end-use products with a soft, pleasant, and non-sticky after-feel. Emollients come from various petro- or bio-based chemical families, with silicone oils, hydrocarbons, and esters being the most prominent. Silicones possess exceptional physicochemical and sensory properties, but their high chemical stability results in very low biodegradability and a high bioaccumulation potential.
Nowadays, consumers are increasingly conscious of environmental issues and demand more environmentally friendly products. This awareness strongly encourages the cosmetics industry to develop bio-based alternatives to silicone oils. Finding effective silicone-free emollients requires a deep understanding of the molecular origins of emollience. This review explores the relationships between the molecular structures of emollients and their physicochemical properties, as well as the resulting functional performances, to facilitate the design of alternative oils with suitable physicochemical and sensory properties.
The molecular profile of an ideal emollient is defined in terms of chemical function (alkane, ether, ester, carbonate, alcohol), optimal carbon number, and branching to create an odorless oil with good skin spreading properties. Since no single carbon-based emollient can fully imitate the non-sticky and dry feel of silicone oils, it is beneficial to blend alkanes and esters to significantly improve both sensory properties and the solubilizing capabilities of the synergistic mixture, especially towards polar ingredients such as sun filters, antioxidants, and fragrances.
Finally, it is demonstrated how modeling tools (QSPR, COSMO-RS, and neural networks) can predict, in silico, the key properties of hundreds of virtual candidate molecules. This enables the synthesis of only the most promising candidates whose predicted properties align closely with the desired specifications.
Keywords: Bio-based emollients, Volatile silicones, Top-down approach, Structure/properties relationships, Predictive tools
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