Aqueous mixtures of di-n-decyldimethylammonium chloride/polyoxyethylene alkyl ether: Dramatic influence of tail/tail and head/head interactions on co-micellization and biocidal activity

► Nonionic surfactants inhibit the biocidal activity of quaternary ammonium surfactants. ► Co-micellization decreases the concentration of unimers of the biocidal surfactant. ► Cationic unimers exhibit a biocidal activity unlike micellized cationic surfactants. ► The biocidal activity of cationic surfactants is maintained when mixed with C10Ej. ► The biocidal activity of cationic surfactants is strongly inhibited with C12Ej.