276 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS In this work, the conditioning effects of dimethicone, dimethicone copolyol, and amodimethicone are investigated. The performance of these silicones is discussed in terms of silicone deposition onto hair surface and alteration in the characteristics of hair. EXPERIMENTAL MATERIALS Samples of silicone were obtained from Shin-etsu Chemical Co. (KF-96, X-21-7501G, KF6005, X-22-4110, and X-22-4104), Dow Corning Toray Silicone Co. (SH200, SH377X, and SM8702C), and Toshiba Silicone Co. (TSF451). All of the chemical ingredients for formulating shampoos were of commercial grade and were utilized without further purification. Table I shows the abbreviated designations for the silicones utilized. METHODS The following analytical instruments equipped with standard-type laboratory appara- tuses were utilized: a scanning electron microscope (JEOL JSM-840), an electron probe microanalyzer (Tracor Tothern TN-503), an inductively coupled plasma (ICP) emission spectrometer (Seiko Instruments & Electronics Ltd. SPS-1200A), and a kinetic frictional coefficient meter (Nippon Rheologykiki Co., Type NRF-II). The method of determi- nation of the critical surface tension of hair, estimated from the wetting force and the kinetic frictional coefficient measurement on a rotating nylon pulley, was done in accordance with the method described elsewhere (1). Measurement of dynamic combing force (2) during the shampooing process was performed with the modified combing method as described previously (1,3). The procedure for determining silicone deposition is as follows: Approximately 0.5 g of hair sample, normal Japanese female hair with no history of chemical treatment, was extracted twice with 50 ml of chloroform for 20 min. The chloroform was removed by using an evaporator, and was replaced with 5 to 20 ml of methyl isobutyl ketone (MIBK) in order to dissolve the silicone. This solution was analyzed with an ICP emission spectrometer. Correction of silicone deposition on the untreated hair was conducted by analyzing hair samples that were not subjected to silicone deposition study. RESULTS AND DISCUSSION DIMETHICONES (POLYDIMETHYLSILOXANES) Polydimethylsiloxanes (PDMS), also called dimethicones, were among the first com- mercially available silicone products. PDMS, having excellent lubricating properties and being utterly water-insoluble, form very hydrophobic films on the hair surface, and this is the reason why PDMS are frequently found in rinse conditioners, hair sprays, and styling mousses. Figure ! shows the kinetic frictional coefficient (}Xk) of hair fibers treated with PDMS of various molecular weights (Mw). It can be seen from the figure that the formation of PDMS film on the hair surface causes a decrease in Ix k values, and

CONDITIONING AGENTS 277 Table I Silicones Used in This Work and Their Abbreviations Name Structures Abbreviations (trade name) Dimethicones (polydimethyl- siloxanes) Dimethicone copolyols (silicone glycol copolymers) Amodimethicone (aminofunctional silicones) CH 3 CH 3 •H3 I I (KF-96) CHs- SiO4SiO•} • Si-CH 3 PDMS (SH200) ] x] ' x ] (TSF451) CH3 CH3 CH 3 (X-21-7501G) CH 3 CH 3 CH 3 CH 3 CH3-piO--•piO •piO)-- Si- CH 3 n I CH 3 CH 3 (CH2) 3 CH 3 O(C2H40)aH CH 3 CH 3 OH I I x CH 3 CH 3 (CH2) 3 NH(CH2)2NH 2 POES (SH377X) (KF6005) (X-22-4104) (X-22-4110) ADMS (SM8702C) the magnitude is dependent on the Mw of PDMS (the }x k with untreated hair is 0.18). The •L k values increase in linear relation to the Mw, but unexpectedly start to decrease when the Mw exceeds the value of approximately 2 X 10 4. PDMS with extremely high Mw (Mw exceeding 105) are especially effective in changing the lubricity of hair surface O. 20 0.18 0. 16 0.14 0.12 O. 10 104 lO s • of PI)• Figure 1. Effects of molecular weight of PDMS on the kinetic frictional coefficient of dry hair fibers.