High molecular weight silicones are known for outstanding hair conditioning and protecting properties. A pronounced silicone character gives rise to a smooth and soft feel in hair, in addition to manageability and combability. Yet while conditioning efficacy usually increases with the molecular weight of the silicone, high molecular weight silicones are difficult to use due to their hydrophobic and viscous character. In shampoos, they can cause turbidity and/or separation, and in conditioners, their homogeneous distribution is difficult to achieve. Furthermore, buildup on hair over time can become an issue.
One approach to overcome these limitations is to incorporate organic modifications onto the silicone backbone. Especially suited for this task are cationic groups that can improve processability, solubility, deposition and substantivity. Damaged hair in particular forms anionic centers on the protein surface—where cationic conditioning agents show improved attraction and substantivity via Coulomb interactions. But even for organomodified silicones, increased molecular weight results in difficult formulation, as they too are high molecular weight silicones and thus highly viscous and difficult to handle. However, when delivered as an emulsion, small droplets of the high molecular weight silicone are pre-formed, which can be easily mixed into cosmetic formulations.
Especially beneficial to the formulator are themodynamically stable microemulsions of very fine silicone droplets, i.e., smaller than the wavelength of visible light, which are therefore also transparent. This approach using fine droplets was employed to develop a microemulsion based on high molecular weight silicone quaternium-22. Its abilities to condition and protect hair were then compared with a silicone quaternium-16 product, as discussed here.