Dielectric study of relaxation in anionic alkylammonium carboxylate surfactants and related non-ionic molecules

Abstract

The dielectric absorption between 10 and 10⁵ Hz of n-octylammonium carboxylate surfactants [CH₃(CH₂)₇⁺NH₃^–O₂C(CH₂)_n CH₃, n= 12, 14, 16 and 18] and n-octylammonium 9-anthranoate, in a polystyrene matrix, arise largely from segmental rotations which include the ⁺NH₃^–O₂C unit. Dielectric absorption maxima for small segment relaxations occur at lower temperatures with an Eyring enthalpy of activation of the order of ΔH_E≈ 10–25 kJ mol^–1. The medium, whether a polystyrene matrix, a polypropylene matrix or even the pure material, does not inhibit such small segment relaxations in these surfactants. The presence of an ionic grouping in a long-chain molecule produces relaxation characteristics similar to those of non-ionic analogues such as long-chain aliphatic esters. The higher-temperature absorption appears to contain relaxation contributions from larger segments. This absorption, however, overlaps with contributions from other processes.