AMINE ADSORPTION ON KERATIN 297 4OO o o- -o 60. • 3oo [] [] 8o //?/,,' • d // _E / ,',,, © 200 / ./ ,/ ¾ /o / ./' • /'/,,- //////=' E //.//' '• 100 I I I I I I I I I I I I I I I I I I I I I 4-0 3.5 3'0 2'5 2.0 -log Jequilibrium ½oncentrotionJ Figure 8. Adsorption isotherms at 40 ø, 60 ø, and 80øC ooe dod½c¾1amin½ on wool at pH • 8 in the o(OA M N•C1. 120 o ø 100 • 80 ..,.... •, 60 .+_. E 40 .•_ ._ '5 20 ß ß 40 ...... 60' ...... 80' ß ßo ß I I I I I I I I I 4.0 3-5 3.0 2.5 -log {equilibrium concentrotion) Figure 9. Adsorption isotherms of diaminododecane at 40 ø, 60 ø, and 80 ø of diaminododecane on wool at pH - 8 in the presence of 0.1 M NaC1.

298 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS TABLE II Standard Affinity (-- A#ø), Enthalpy (--AHø), and Entropy (AS ø) of Sorption at pH 8 of Dodecylamine and 1,12-Diaminododecane on Wool Over the Temperature Range 40ø-80øC Dodecylamine Diaminododecane -- A/t ø _ AH ø AS ø _ A/t ø _ AH ø AS ø T(øC) Kcal/mole cal/mole cal/mol/deg Kcal/mole cal/mole cal/mol/deg 40 2.654 1.604 approx. 60 2.877 0 8.5 1.687 250 80 2.993 1.782 4.3 diamine on the other hand clearly indicate from the decrease in saturation with temperature that adsorption is an exothermic process. An estimate of standard enthalpy (AH ø) for the adsorption of diaminododecane and standard entropy (AS ø) for the adsorption of both classes of amine were derived from the expression (28): in (D•s•) AHø AS o =-•-• R ' where D t is the concentration of adsorbate at equilibrium (mole/Kg dry fiber), and Ds is the corresponding concentration of adsorbate in the solution phase (mole/liter). The more usual form of the above expression is one in which the partition coefficient (Dr/Do) is considered as a ratio of activities (at/as). Although the activity coefficient of the adsorbate on the fiber can never be determined with certainty, variability with concentration is eliminated by selecting a constant Dt and determining the D s values for each temperature from the point at which the chosen Dt intersects each isotherm (29). This procedure could not be applied to the present study, however, because of the uncertainty of experimental measurement at low concentrations of diamine. The thermodynamic parameters are therefore to be considered as approximations only. The enthalpy of adsorption for the diamine was estimated from the slope of a plot of In (Dr/Ds) against 1/T (øK), and found to be approximately - 250 cal/mol, a value which is comparable to the heats of adsorption of Orange II and HCI (less than 0.8 Kcal/mole) to wool from 60 ø to 100 ø (30). The standard entropy (AS ø) was derived from a plot of standard affinity (Aø/z) vs T (øK) where -A/z ø = RT ln(Dt/D s). The values are shown to be in the range of + 4 to +8 cal/deg/mole (Table II) for diaminododecane and dodecylamine respectively. Because the enthalpies of adsorption are close to zero, the affinity of long-chain amines for keratin fibers must be derived solely from the gain in entropy. Such a conclusion may be relevant to other surface-active cationic species in view of a recent study which found that the adsorption of cetyl pyridinium chloride on carbonized wool is virtually athermal (13). CONCLUSION The results of this study allow broad conclusions to be reached concerning the manner in which long-chain amines interact with keratin fibers. The increase in amine uptake