Empirical Correlations between Krafft Temperature and Tail Length for Amidosulfobetaine Surfactants in the Presence of Inorganic Salt
2012
Chu, Zonglin | Feng, Yujun
Long-chain amidosulfobetaine surfactants, 3-(N-fattyamidopropyl-N,N-dimethyl ammonium) propanesulfonates (n-DAS, n > 18), are insoluble in pure water due to their high Krafft temperature (TK), while they are soluble when inorganic salt is added to the surfactant solution as the TK of these zwitterionic surfactants is decreased. The influence of the salt content and ionic species of the added electrolytes on the TK of the series of amidosulfobetaine surfactants was examined by means of UV–vis spectrophometry and visual inspection. It was found that the TK of these surfactants depends strongly on not only the hydrophobic alkyl length (n), but also the salinity of the aqueous environment. When the salt concentration is increased from 0 to 100 mM, the TK shows a sharp decrease; when the salinity is fixed between 100 and 2000 mM, the TK varies linearly with n with a slope of ∼7.7 irrespective of the salt species and the salt content. When the salt concentration is further increased above 2000 mM, a linear function is still observed, but the slope increases slightly.
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