348 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 0.7 0.6' 0.5 , 0.2 Tress length First (0), seoond (•) and third (•) (o) -combing force 1.2 5.8 { •.5\ C) teflon .1..0 0.8 0.6 0.4 0.2 0 Tress length First (o),second (s) and third (V) combing , . -120 • 0.8- ß 100 v • •o 0.6 80 ø • • • 0.4 60 =• 40 •o 0.2 20 o• 0 • b) polyet Tress length First (o),second (D) and third combing mo 0 • -8.4 ! -2 • d) polyc -3 Tress length First (o),second (D) and third (V) combing Figure 4. Triboelectric charge distributions on stearalkonium chloride-treated hair after multiple combings with combs made of various polymers no discharging between combings. with the highest charge density located in the upper portion of a hair tress, should not result in "fly-away" hair. This observation is compatible with the well-documented antistatic nature of cationic surfactants which are widely used as static electrification and friction-lowering agents in hair-conditioning products. Combing of PDMPDAMC-modified hair yields high-intensity charge distributions centered around the tip-end portion of a hair tress (Figures 5a-c). Following the pre- vious line of reasoning, this has to be attributed to a widened electrochemical gap between contacting materials as well as an increased combing force observed for PDMPDAMC-modified tresses (Figure 5a). Such charge distributions result in the "fly away" phenomenon which is known to plague PDMPDAMC-containing formulations. CONCLUSIONS Simple single-peak charge density profiles during the combing of hair at 50% RH, as reported by Lunn and Evans (4), are not observed in our results obtained under lower RH conditions. Measurements performed using insulator combs indicate that the typ- ical charge distribution for clean hair fibers consists of two or three distinct peaks, with the one from disentanglement of tip ends contributing only to a small extent to the total generated charge density. The origin of a large peak at the upper portion of the tress was not unequivocally ascertained. We speculate that the initial contacts between polymer-comb surface and keratin result in electron transfer and produce a very high

TRIBOELECTRIC CHARGE DISTRIBUTIONS ON HAIR 349 1. tress length O - oc•bing force First (0), second (0) and third (•7) c) poly•z• tress lergth First (O), second (•) and third 120 •:• 4' lOO •' B0 • 3 •2. 60 8 . o 0 0 b) t•flon • tress len• First (O), s•oond (1•) • third (•) •mbmg Figure 5. Triboelectric charge distributions on PDMPDAMC-modified hair after multiple combings with combs made of various polymers no discharging between combings. potential on the comb surface, inhibiting the charge-exchange process in the lower part of the tress. This hypothesis finds support in metal-combing charging characteristics which do not exhibit the initial peak but is, however, not consistent with the observed enhancement of this peak by insulator combs loaded to the potential of the opposite sign. The influence of comb work function and hair surface modification on charge distribu- tion profiles are generally similar to the ones observed in the experiments involving surface rubbing electrification and can be rationalized in terms of the band model of the electronic structure of polymers and metals, assuming certain characteristic values of work functions for each material. Superimposed frictional effects, introduced by surface treatments, distort the division of transferred charge representative of untreated hair by altering the intensity of friction-dependent middle and tip-end peaks. REFERENCES (1) J. Jachowicz, G. Wis-Surel, and L. J. Wolfram, Directional triboelectric effect in keratin fibers, Text. Res. J., 54(7), 492 (1984). (2) J. Jachowicz, G. Wis-Surel, and M. L. Garcia, Relationship between triboelectric charging and surface modifications of human hair, J. Soc. Cosmet. Chem., 36, 189 (1985). (3) G. Wis-Surel and J. Jachowicz, unpublished results. (4) A. C. Lunn and R. E. Evans, The electrostatic properties of human hair, J. Soc. Cosmet, Chem., 28, 549 (1977).