352 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS The treatment of wool with anionic and cationic surfactants, alone and consecutively in either order, is the subject of this paper. The results are considered in the light of the rearrangement proposed by Finkelstein and Laden (3) to account for conditioning of human hair with cationic surfactants. EXPERIMENTAL MATERIALS Merino wool top that had been further extracted with light petrol, ethanol, and water was used for all wool experiments. Hair samples were obtained from a hairdresser. Sodium dodecylsulphate (SDS, molecular weight 288) and cetyltrimethylammonium bromide (CTAB, m. wt. 364) were pure commercial samples. Fluorescent anionic (P-6, m. wt. 391) and cationic (CP-6, m. wt. 391) surfactants, based on the pyrazoline chromophore, were prepared by Dr. I. W. Stapleton of this laboratory as their ammo- nium salts (7,10). P-6 has been shown to have surfactant properties similar to those of sodium cetyl sulphate (7,9,10). Based on molecular weight and length of hydrophobic side-chain, CP-6 would be expected to have properties similar to CTAB. METHODS Wool top samples (5 g) were treated with SDS or P-6 at pH 3.5 (0.01 M acetic acid) in an Ahiba Turbomat dyeing machine, liquor/wool ratio 60:1. The samples were treated for 60 min at 60øC, then brought to 80øC over 30 min and heated at 80øC for 30 min. Wool treatments with CTAB were carried out at pH 7.0 (0.05 M phosphate) using the same dyeing cycle as for SDS. Both SDS and CTAB were completely taken up by wool under these conditions. After-treatments with CP-6 or CTAB were carried out at pH 7.0 (0.05 M phosphate), 60øC, liquor/wool 40:1. After-treatments with P-6 were carried out at pH 3.5 (0.01 M acetic acid), 60øC, liquor/wool 40:1. CP-6 and P-6 contents of wool were analyzed by measuring the optical density at 350 nm of the treatment solutions after dilution with 50% aqueous ethanol. This method determines the total of free and complexed fluorescent surfactant because the anionic-cationic surfactant complexes are dissociated in this solvent. Anionic and cationic surfactant contents of hair samples were measured by extracting duplicate samples (0.25 g) with isopropanol/pH 7 buffer 1:1 (10 ml) at 60øC for 60 min. The extracted samples were rinsed with water (2 ml) and the rinsings added to the extracts. Each extract was evaporated to dryness by heating to approximately 80øC in a stream of nitrogen. One part was then treated for 1 hr in a steam bath with 1 M HC1 (1 ml) and then evaporated to dryness as previously. This procedure was shown to be effective in hydrolyzing sodium dodecylsulphate. The hydrolyzed and unhydrolyzed extracts were then analyzed for surfactant content by carrying out two-phase titration (11) using sodium dodecylsulphate (10-3 M) or Hyamine 1622 (10- 3 M), respectively. Cationic surfactant content was determined from the SDS titer for the hydrolyzed samples. Anionic surfactant content was determined by adding the SDS titer for the hydrolyzed samples to the Hyamine 1622 titer for the unhydrolyzed sample.

CATIONIC-ANIONIC INTERACTIONS 353 RESULTS AND DISCUSSION The uptakes of the cationic surfactant CP-6 by untreated wool and by wools that had been treated with SDS are shown in Figures 1 and 2. The uptake of CP-6 on the untreated wool is almost complete in 60 min at 60øC (Figure 1). The initial uptake of CP-6 is faster when the wool contains either 0.5 or 1.0% of SDS, but on prolonged treatment the cationic then desorbs from the 1.0% sample but not the 0.5% sample. When wool contains 5.0% of SDS, much lower initial sorption of CP-6 is observed, lOO 80 60 40 20 pH 7, 60 ø 0 0 20 40 60 treatment time (minutes) +0.0 % [] 0.5 % '•' 1.0 % +5.0 % Percent anionic surfactant (SDS) pretreatment Figure 1. % Uptake cationic CP-6 (1.0% applied).