Langmuir monolayer behavior of sodium hexadecyl sulfate controlled by bolaform counterions

The influence of the bolaform salts in aqueous subphase, ethanediyl-α,ω-bis(ethyldimethylammonium bromide) (Bola2Et), alkanediyl-α,ω-bis(methyl dimethylammonium bromide) (Bolan, n = 4, 6, 8) and alkanediyl-α,ω-bis(benzyldimethyl ammonium bromide) (Bolanph, n = 2, 4, 6, 8), on the monolayer behavior of sodium hexadecyl sulfate (SHS) has been studied by Langmuir film balance technique. The NMR measurements revealed the benzene rings of these counterions were penetrated among the headgroups of SHS except Bola2ph. This made the interaction of Bolanph with SHS stronger than that of Bolan. With increasing n of both Bolan and Bolanph from 4 to 6, the limiting molecular area (AE) monotonously increased. For Bola8ph, the long spacer chain was bent toward the alkyl tails of SHS, which made the AE reduced under the strong interaction of both. All these suggested that the monolayer behavior of SHS could be controlled by the bolaform counterions in aqueous subphase.