2010 TRI/PRINCETON CONFERENCE 131 However, the percentage increases in average contact angle for conditioner-B treated virgin hair is only 13.37% in diiodomethane, and 15.80% in benzyl alcohol. These changes are signifi cantly less than those for the bleached hair at the same liquid /air interface. The differences in percentage changes of average contact angles between conditioner-A and conditioner-B treated hair fi bers may be attributed to the different molecular struc- ture of active ingredients in each formulation. Quaternium-91 in conditioner-A has two long alkyl carbon chains (C22) and delocalized positive charge, which made this ingredi- ent a very good conditioning agent on both virgin and bleached hair, whereas behetrimonium Figure 1. Contact angle values of the control and conditioner-A treated bleached hair. Figure 2. Contact angle values of the control and conditioner-A treated virgin hair. Figure 3. Contact angle values of the control and conditioner-B treated bleached hair.

JOURNAL OF COSMETIC SCIENCE 132 methosulfate in conditioner-B has higher positive charge density, and certainly has strong interaction with the damaged, negative-charged hair surface such as bleached hair (7). Therefore, conditioner-B showed a better conditioning effect on the bleached hair with a larger percentage increase of the contact angle values after the treatment. CHANGE IN SURFACE ENERGY AFTER CONDITIONING Data of calculated surface energy of hair fi bers are summarized in Tables I and II. The surface energy of conditioner-A treated bleached and virgin hair reduced by 29.06% and 31.77%, respectively (Table I), which indicated that the conditioner-A demonstrated the similar conditioning effect on both hair types, and these results corresponded well with results on percentage changes in contact angles of conditioner-A treated bleached and virgin hairs. Reductions in hair surface energy after conditioner-B treatment are summarized in Table II. It is observed that the average surface energy decreased by 33.72% and 27.64%, Figure 4. Contact angle values of the control and conditioner-B treated virgin hair. Table I Calculated Surface Energy of Conditioner-A Treated Bleached and Virgin Hair Bleached hair Control Treated % Change Polar surface energy, σSP (mJ/m2) 2.18 1.79 −17.98 Dispersive surface energy, σSD (mJ/m2) 27.65 19.38 −29.91 Total surface energy, σS = σSP + σSD (mJ/m2) 29.83 21.17 −29.06 Virgin Hair Control Treated % Change Polar surface energy, σSP (mJ/m2) 2.48 1.77 −28.68 Dispersive surface energy, σSD (mJ/m2) 16.41 11.12 −32.24 Total surface energy, σS = σSP + σSD (mJ/m2) 18.89 12.89 −31.77