DYNAMIC ELECTROKINETIC AND PERMEABILITY ANALYSIS 103 ylamine, trimethylsilylamodimethicone/octoxynol-40/isolaureth-6/propylene glycol, fragrance, deionized water. ß Conditioner H: water, denatured alcohol, betaine, cetearyl alcohol, petrolatum, citric acid, horsetail extract, glyxolic acid, laureth-2, sodium cetearyl sulfate, silica, fra- grance. ß Conditioner I: water, cetearyl alcohol, behentrimonium chloride, cetyl esters, amodimethicone, dimethicone copolyol, polyquaternium-11, panthenol, tallowtri- monium chloride, fragrance, nonoxynol-10, propylparaben, phenoxyethanol, meth- ylparaben, DMDM hydantoin. ß Shampoo: water, SLES, SLS, cocamidoprobyl betaine, lauramide DEA, ricinoleami- dopropylethyldimonium ethosulfate, panthenol, dimethicone copolyol, amodimethi- cone (and) tallowtrimonium chloride (and) nonoxynol-10, polyquaternium-11, mica and TiO 2, citric acid, fragrance, DMDMH and iodopropynyl butylcarbamate, 1onza- glydant plus. RESULTS AND DISCUSSION MODEL SURFACTANT AND EMULSION SYSTEMS The experimental protocols were the same as those employed in the previous work (1). In each plot (Figures 1-7) the first measurement period shows five datapoints obtained for the untreated fibers. The ranges of the measured streaming potential, conductivity, flow rates, and zeta potentials for untreated hair were the same as those reported earlier (10). In all figures presented in this paper the fifth datapoint on zeta potential and flow rate curves were normalized to - 15 mV and 3.5 cm3/sec, respectively. This was done to facilitate the comparisons of the curves obtained for different formulations. However, the calculations of the thicknesses of deposited layers were performed on actual, unad- justed numbers obtained in the experiments (1,10). DEPA traces for several types of conditioning agents widely employed in conditioner formulations are presented in Figures 1-3. The results for two cationic surfactants, behenyltrimethylammonium chloride (BTC) and linoleoamidopropyldimethylethyl am- monium ethylsulfate (LAEDES), are shown in Figure 1. LAEDES is a water-soluble liquid, while BTC is a solid, forming dispersions in the aqueous medium. For both surfactants, following the treatment there is a reversal of the sign of zeta potential as a result of the adsorption of cationics on the fiber surface. After reaching the maximum, immediately after the treatment for LAEDES and after three rinsing cycles for BTC, zeta potentials decrease and attain an equilibrium value that reflects the presence of a stable layer of a conditioning agent on the fiber surface. This pattern is typical for the interactions of cationic surfactants with hair, and was previously described for stearyldimethylbenzylammonium chloride and cetyltrimethylammonium chloride (10). As suggested in reference (10), a decrease in the value of zeta potential may be caused by a desorption of the surfactants into the test solution, although a possibility of their rearrangement or diffusion in the opposite direction, i.e., into the bulk of the fibers, cannot be excluded. If desorption into the test solution is responsible for a decrease in zeta potential, than a slower rate of reduction in zeta potentials, as in the case of BTC as compared to LAEDES, points to a higher affinity of this surfactant to hair. On the other hand, a partitioning of adsorbed species inside hair is also expected to be faster for

104 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS 10- + + + + ++ % ++ [] + % ø o ++ [] ++ ++ -20 0 1'0 2'0 3'0 40 5'0 6'0 7'0 4.00- TIME ( min ) [] LAEDES + BTC 3.50- • 3.00- • 2.50- •0 2.00- LL 1.50- 25 + + + + 1.0C 0 1•0 20 30 40 S'0 6'0 '7'0 TIME ( min ) o LAEDES + BTC 80 20- 5_ ,•... 0 0 + + 10 20 3'0 4'0 5'0 6'0 7'0 TIME ( rnin ) ,• LAEDES + BTC J Figure 1. Zeta potential (a), flow rate (b), and conductivity (c) as a function of time for hair treated with 0.5% w/w solutions of behenyltrimethylammonium chloride (BTC) and linoleoamidopropyldimethylethyl ammonium ethylsulfate (LAEDES).