Characterization of the deposition of silicone copolymers on keratin fibers by streaming potential measurements

• Cationic silicone copolymer deposition on keratin monitored by streaming potential.
• Amino silicone polyether block copolymer screened charges more efficiently than conventional aminosilicone.
• Long ethylene oxide block facilitated the silicone block copolymer unfolding.
• At low pH, silicone block copolymers overcompensated substrate surface charges.

This paper compares the deposition of two aminofunctional silicones on hair that are both widely used as textile finishes and hair conditioners. The two polymers had different structures: a linear amino-polyether-silicone block copolymer (ABn) with hydrophilic character and a conventional pendant aminodimethicone (AMD) with the same amine content. The deposition (irreversible adsorption) on keratin fibers as a function of pH, concentration, and treatment time was studied using streaming potential measurements. The polymer deposition was also measured independently by analysis of the silicon element content of the treated hair samples. With ABn, the deposition reached a plateau after the reversal of the hair charge (overcompensation). In contrast, with AMD, the reversal of charge was not observed and the deposition was much higher, suggesting a more prominent role of hydrophobic interactions. A recent model of streaming potential was used to interpret the data.

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