Hair tip-root silicone selectivity

Hair in root is typically pristine but also easily damaged by environmental exposure, mechanic abrasion and chemical treatments. On the other hand, the hair tip is typically more damaged and hydrophilic. Because undamaged hair is similar to hair in root, while bleached hair is similar to damaged hair in tip, hair tip-root silicone selectivity can be defined as the ratio of the RSSL for bleached hair to the RSSL for undamaged hair. Silicone trends to deposit more on undamaged hair than bleached hair. The hair tip-root silicone selectivity is always below 100%, and a higher the percentage indicates that silicone could distribute evenly along the hair tress from tip to root. As shown in Figure 6, both GHPTC and the polyAPTAC-ACM/GHPTC mixture have relatively high percentages of SPS, LPS/SPS and ADM deposition. ADM has the highest result among all silicone emulsions and is the preferred choice for damaged hair because it has positively charged groups that could adhere to negatively charged groups on the surface of damaged hair through ionic interaction. The tip-root selectivity data for shampoos with no polymer and PQ-10 have no meaning since the RSSL is less than 0.05, which indicates there is almost no silicone deposit on either undamaged hair or bleached hair.

Contact angle measurement

After depositing on the hair surface, a silicone coating will provide bleached hair with a more hydrophobic surface, better dry combing force reduction, soft feel, more lustrous appearance, and improved manageability. The dynamic contact angle of the undamaged hair and bleached hair treated with different shampoo samples containing ADM was measured and shown in Figure 7. The undamaged hair was very hydrophobic, with a contact angle of 108.5° that slightly decreased after 100 seconds. The bleached hair was very hydrophilic with a contact angle of 41.52° that decreases to almost 0° after 100 seconds. Bleached hair treated with the polyAPTAC-ACM/GHPTC mixture exhibited the highest contact angle after 100 seconds, followed by the GHPTC, PQ-10 and no-polymer samples. A higher contact angle indicates a more hydrophobic surface and more silicone deposition on hair. The results correlate well with the results from the silicone deposition study mentioned earlier.


source from https://www.personalcaremagazine.com