Synthesis and Physicochemical Properties of Double-Chain Cationic Surfactants

In this study two types cationic surfactants were synthesized, purified, and characterized in our laboratory. One them is a series of cationic surfactants, a two tail–one head surfactant, <i>N</i>,<i>N</i>-dialkyl-<i>N</i>,<i>N</i>-diethylammonium bromide, abbreviated as “<i>m</i>-0-<i>m</i>” (<i>m</i> = 10, 12, and 16). The other type is <i>N</i>,<i>N</i>′-dialkyl-<i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethyl-<i>N</i>,<i>N</i>′-ethanediyl-diammonium dibromide, two tail–two head surfactants, abbreviated as “<i>m</i>-2-<i>m</i>” (<i>m</i> = 12 and 16). Once NMR spectra (¹H NMR, ¹³C NMR) for all the gemini surfactants that were synthesized were taken, then the melting temperatures (<i>T</i>_M)­ were measured. These surfactants have very high surface activity. The main goal of our study was to examine some properties of these two tail cationic surfactants by manipulating their dimeric structure. The effects of alkyl chain length and headgroup on surfactant self-assembly in solution were investigated. Critical micelle concentrations (CMC), degree of micelle ionization (α), and Krafft temperatures (<i>T</i>_K) of 1 wt % aqueous solutions of these surfactants were determined by conductance measurements. Krafft points were found to be dependent on the number of carbon atoms in the alkyl chain and decreased by the addition of the electrolytes. The absence of the spacer group, peculiar to these twin tail cationic surfactants, may confer relatively low flexibility to the molecules, with potential implications on the interfacial properties, namely, on micellization