TRIBOELECTRIC CHARGING OF HAIR 207 Q/A-10 9 (C.cm r2) 2 1 0 -1 -2 -3 -4 -5 -6 (a) Polycarbonate Root to Tip •Time [min] Tip to Root ß Sodium Dodecyl Sulfate (1%) O Sodium Tetradecyl Sulfate (1%) ] O Sodium Hexadecyl Sulfate(1%) I-• •4 .• .• i..0_ ...... ß E•cosanoic Acid (padially soluble, 0.5%) • 0 Eicosawater,basic0.5%)inAcid(cSolution soluble Q/A.10 9 (C.cm_2) 6 5 4' 2 1 '0 -1 -2 -3 -5 (b) Stainless Steel Root to Tip Tip to Root (e) Teflon Root to Tip Tip to Root Time [min] Figure 10. Kinetic curves of tribocharge generation on keratin fibers modified with the complex PMAPTAC-anionic detergents of various chain lengths. Fibers were treated for 2 hours at lg/dl PMAPTAC solution, rinsed with H20 and kept in aleionized water for 1 hour, then exposed to anionic surfactant for 100 min followed by soaking in H20 for 12 hours. rubbing material, presented in Figures 9 and 10, are the consequence of different treatment procedures given in detail in figure descriptions. The rates of charge decay of complex-treated fibers were usually exponential and fast as is exemplified by the data shown in Figure 5. This is justified by the presence of the saturated monolayer of cationic polymer which was shown (Figure 8) to increase considerably the ionic surface conductivity of the fibers. EFFECT OF FIBER REDUCTION ON TRIBOELECTRIC CHARGING Reduction of keratin fibers with both THPC and TGA results in a change in the electrochemical potential of the fiber surface. In the case of a nylon © probe, the direction

208 jOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS of the charge transfer was reversed in comparison with untreated fibers for rubbing from root to tip (for both THPC- and TGA-modified keratin, Figure 1 la,b). The sign of the charge generated by chitosan acetate was negative only for TGA-treated keratin (Figure llb). The signs and magnitudes of charges generated by rubbing from tip to root are in accord with all our previous observations and with the data obtained for rubbing in the direction from root to tip. (3) Q/A .10 9 Root to Tip Tip to Root (C.om-2) 6 1 0 in] , i•n] -4 56 t 0 Stainless Steel 0 Nylon (b) Root to Tip ß Teflon ß Poly(methyl methacrylate) & Polycarbonate ß Chitosan Tip to Root . . li•e [m•n] i .• .• .• .'f Figure 11. Tribocharge generation on keratin fibers reduced with (a) THPC (15 minutes at 23øC) and (b) TGA (10.6% solution, pH = 9.2, 15 min at 37øC). PMMA film, which is characterized by a work function lower than keratin and which charges untreated fibers negatively in both modes of rubbing, showed an unexpected characteristic. It initially produced a low density of negative charges on the fibers, but then the direction of charge transfer was reversed with the polymer film acting as an acceptor (Figure 1 la,b). If the electrochemical potential of the fiber surface is increased, as is suggested by the direction of charge transfer for rubbing with chitosan acetate and nylon © probes, then PMMA film should exhibit an even stronger tendency to charge keratin negatively. We cannot offer, at the present time, any reasonable expla- nation for this unexpected behavior of PMMA film. Oxidation of reduced keratin with H20 2 did not have any additional influence on tribocharging, and the obtained kinetic curves resemble those obtained for reduced hair. The rates of charge decay for reduced hair were of the same order of magnitude as for untreated fibers (tv•6 • = 11.4 min for (rl = 3.20 ß 10 -9 C/cm 2 at 28% RH for hair reduced with TGA and oxidized with H202). EFFECT OF FIBER BLEACHING ON TRIBOELECTRIC CHARGING Hair bleaching resulted in a very small change of charging characteristics for both modes of rubbing as compared to untreated fibers (Figure 12). The PC probe generated • The time after which surface density decayed to one-sixteenth of its initial value.