Synthesis, surface activity and antielectrostatic properties of new soft dichain cationic surfactants

Two homologous series of soft structures, i.e., the diesterquat-type N,N-dimethyl-N,N-bis[2-(alkoxycarbonyl)ethyl]ammonium bromides (2xCnE-Br, n=10, 12) and the diamidequat-type N,N-dimethyl-N,N-bis[2-(N-alkylcarbamoyl)ethyl]ammonium bromides (2xCnA-Br, n=8, 10, 12), were synthesized according to a technologically convenient procedure. The equilibrium surface tension isotherms of investigated ammonium salts solutions were measured by a pendant drop shape analysis method. Air/solution interface adsorption behavior of selected cleavable ester and amide-containing cationic surfactants was examined both experimentally, and theoretically upon the surfactant pH dependent cleavage. It was found, that diamidequat-type surfactants exhibit much higher surface activity than their diesterquat-type counterparts with the same number of carbon atoms in the hydrophobic tails. Moreover, at CMC (critical micellization concentration) they much efficiently lower the surface tension down to ca. 25mN/m. They are also characterized by higher stability with respect to the hydrolysis process. The results of the present study may prove useful in the understanding of the effect of changes in molecular structure and in the environment around the diesterquat-type and diamidequat-type surfactants on their self-aggregation behavior at the interfaces. The antielectrostatic properties were investigated in relation to the standard N,N-(dialkyl)-N,N-dimethylammonium bromides (decyl C10C10-DAB and C12C12-DAB, respectively) by measuring the surface resistance (Rs), the half-charge decay time (τ1/2), and the maximum voltage induced (Uind) on low-density polyethylene (LDPE) film and polypropylene (PP) nonwoven fabrics. All investigated salts had very good antistatic properties on the nonwoven fabrics but none on the film, diamidequats providing better antistatic action than diesterquats.