Studies on Metal-Containing Surfactants. IV

Abstract

Emulsifying property of binary aqueous solutions of dodecyl pyridinium chloride (DPC) -metal soap for various hydrophobic organic substances (which will be designated as oils hereinafter) was investigated. The metal soaps used were mainly stearates and ricinoleates of alkaline and alkaline earth metals. Five substances, that is, cottonseed oil (CO, required HLB, 10), liquid paraffin (LP, 12), kerosene (K, 12.5) cetyl alcohol (CA, 15), and dimethyl phthalate (DMP, 15) were employed as the oils. The property was studied chiefly with the mixed solutions of DPC : metal soap=2.5 to 20 : 1 for the range of molar ratio.The emulsifying power of DPC for the oils was not affected by the addition of a small quantity of metal soap (1/1001/1000 mol) but remarkably changed when 1/101/3 mol of the metal soap was added. In the case of sodium ricinoleate, the change in the optimum oil for DPC was inconspicuous, while it was remarkable with the salts of barium, magnesium etc. and K and LP were optimum with a higher degree of emulsification.With the solution having a DPC : metal soap mixing ratio of 0.02 : 0.004 mol/l, stearates showed a particularly excellent emulsifying power, which was not so greatly varied with metals. Laurates were somewhat good, but ricinoleates showed a little inferior emulsifying power being greatly influenced by metals the salts of barium, magnesium and lithium showed better results than other metals. It was a common tendency that every metal soap showed a good emulsifying power for K and LP, but for other oils it became less favorable. The kind of the optimum oil for DPC was not affected by the addition of free fatty acid, its methyl ester or short-chained metallic compounds. The result that stearates possessed the best power for emulsifying property was considerably different from that obtained with wetting power and other properties reported previously. The additivity of HLB observed with nonionic surfactants seemed not to hold for the present mixed solution systems.