Silicone deposition mechanism

Silicone emulsions with SPS, LPS combination of SPS/LPS and ADM are all popular and used in conditioning shampoo formulas in the Asian market. Water-insoluble silicone oils with different droplet sizes are dispersed in aqueous solutions by surfactants. SPS and ADM silicone droplets are smaller than 1 ìm, while LPS droplet is larger than 30 ìm. Aside from silicones, cationic polymers such as PQ-10 and GHPTC are also used for formulating conditioning benefits in shampoo. The deposition of some silicones can be increased significantly by using cationic polymers that form complexes with anionic surfactants in shampoos. The most broadly used deposition mechanism is based on coacervate formation. The polymers are soluble in the undiluted shampoo but become insoluble during the rinsing stage; the polymer surfactant complex then precipitates out of solution and deposits onto the hair through the coacervation process. Meanwhile other actives such as silicone or ZPT in shampoos will be encapsulated inside the coacervate and deposit on hair simultaneously. Many parameters such as polymer types, molecular weight, cationic charge density, silicone emulsion type and the extent of hair surface damage will all affect the coacervate formation, the deposition efficacy and the build-up level after multiple washings. All three cationic polymers in conditioning shampoos can form coacervate during dilution. Silicone oils in SPS and ADM emulsions have small droplets and can be easily encapsulated in the coacervate, resulting in higher deposition levels than the sample containing no polymers. However, silicone oil in the LPS emulsion is larger than 30 ìm and are too large be encapsulated in the coacervate, as shown in Figure 9. The deposition of LPS has a totally different mechanism and is completely dependent on the affinity between the LPS and hair surface. Thus, shampoos containing no polymers could deposit large amounts of silicone due to a high affinity of LPS and the hydrophobic surface of undamaged Asian hair, while there is almost no silicone deposition on bleached Asian hair. Because this kind of deposition on undamaged hair is uncontrolled, the build-up effect is very significant in shampoos without polymers and PQ-10. The polyAPTAC-ACM /GHPTC mixture and GHPTC polymers have a desirable property for suppressing LPS build-up in conditioning shampoos. ADM is the preferred choice for bleached or damaged hair because it has positively charged groups and can adhere to negatively charged groups on the surface of damaged hair through ionic interaction.

source from https://www.personalcaremagazine.com