Small-angle neutron scattering study of aggregate structures of multi-headed pyridinium surfactants in aqueous solution

J HALDAR^a, V K ASWAL^b, P S GOYAL^c and S BHATTACHARYA^a

^aDepartment of Organic Chemistry, Indian Institute of Science, Bangalore 560 012, India

^bSolid State Physics Division; ^cIUC-DAEF, Mumbai Centre, Bhabha Atomic Research Centre, Mumbai 400 085, India

E-mail: jaya@students.orgchem.iisc.ernet.in

Abstract. The aggregate structures of a set of novel single-chain surfactants bearing one, two and three pyridinium headgroups have been studied using small-angle neutron scattering (SANS). It is found that the nature of aggregate structures of these cationic surfactants depend on the number of headgroups present in the surfactants. The single-headed pyridinium surfactant forms the lamellar structure, whereas surfactants with double and triple headgroups form micelles in water. The aggregates shrink in size with increase in the number of headgroups in the surfactants. The aggregation number (N) continually decreases and the fractional charge ({$\alpha$}) increases with more number of headgroups on the surfactants. The semimajor axis (a) and semiminor axis (b=c) of the micelle also decrease with the increase in the number of headgroups in the surfactants. This indicates that hydrocarbon chains in such micelles prepared from multiheaded surfactants adopt bent conformation and no longer stay in extended conformation.

Keywords. Multi-headed pyridinium surfactants; micelle; small-angle neutron scattering.

PACS Nos 61.12.Ex; 82.70.Uv