Effect of counterion structure on micellar growth of alkylpyridinium surfactants in aqueous solution Bijma, K; Rank, E.; Engberts, J.B.F.N. Take-down policy If you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim.Downloaded from the University of Groningen/UMCG research database (Pure): http://www.rug.nl/research/portal. For technical reasons the number of authors shown on this cover page is limited to 10 maximum. This paper describes the influence of counterions on the unidirectional growth of micelles formed by alkylpyridinium surfactants in aqueous solution. It is shown that the growth of spherical micelles to form wormlike micelles is strongly dependent on counterion structure. More hydrophobic counterions induce the formation of wormlike micelles at lower surfactant concentrations. Next to hydrophobicity and the type of substituent, the substitution pattern of the aromatic ring plays the most important role in micellar growth. The formation of a network of entangled, elongated wormlike micelles by alkylpyridinium surfactants with o-hydroxybenzoate and p-chlorobenzoate counterions is discussed in terms of surfactant structure. It is concluded that, next to counterion structure, the microenvironment of the counterion (substituent) in the Stern region and the structure of the surfactant monomer (i.e., the surfactant cation) play the most important role in the formation of these elongated wormlike micelles. Headgroup effects are proposed to be the main driving force for this phenomenon.