Preparation, amphiphilic properties and lyotropic phase behaviour of new surfactants based on sodium monoalkyl α,ω-dicarboxylates

New surfactants based on sodium monoalkyl α,ω-dicarboxylates H3C(CH2)n − 1OC(O)(CH2)m − 1CO2Na (CnCmCO2Na) with various chain lengths were prepared from succinic anhydride (m = 3), azelaic acid (m = 8) and dodecanedioic acid (m = 11). Their physico-chemical properties (Krafft point, critical micelle concentration and kinetics of hydrolysis) were measured and their lyotropic aqueous phase behaviour was investigated by polarized light optical microscopy. To assess the influence of the ester function inside the hydrocarbon chain, sodium monoalkyl azelates and monoalkyl succinates were compared with sodium soaps (m = 0) having a same carbon number. Insertion of an ester group within the surfactant alkyl chain considerably lowers the Krafft point and slightly delays the formation of the first mesophase. The methylene units localized between the ester and the carboxylate groups are equivalent to 0.5 methylene group in their effect on CMC. The rate of hydrolysis of those monoesters depends heavily on the pH and on the CMC. The kinetics is fast and pseudo-first order below the CMC and it is slow and pseudo-zeroth order above the CMC because the ester function is protected from hydrolysis when it is embedded within the micelle core.