EFFECT OF HARD RIVER WATER ON THE SURFACE-PROPERTIES OF SURFACTANTS

The surface properties [effectiveness of surface tension reduction (ga mma(CMC)), critical micelle concentration (CMC), efficiency of surface tension reduction (pC(20)), maximum surface excess concentration (Gam ma(max)), minimum area/molecule at the interface (A(min)), and the (CM C/C-20) ratio] of well-purified anionic, nonionic, and cationic surfac tants, some of which are widely used in daily chemical and industrial products, were investigated at 25 degrees C in hard river water. The s tudied surfactants show somewhat greater surface activity in hard rive r water than in distilled water, but in particular, for anionic surfac tants a marked effect of hard river water on surface active properties was observed. The effect of hard river water on surface active proper ties is, in decreasing order, anionics > cationics > nonionics. For al kyl poly(oxyethylene) glycols, the effect on surface properties is int erpreted in terms of complex formation between the ether oxygen atoms of the poly(oxyethylene) group and divalent hardness ions. The linear relationship between the pC(20) or CMC values and the number of carbon atoms in the alkyl chain observed in distilled water was confirmed in hard river water. For alkyl poly(oxyethylene) sulfates, the slope of the plot indicates an effect of the alkyl chain on adsorption at the a ir/water interface or on micellization similar to that observed for no nionic surfactants in distilled water.