Aggregation of tetrameric acids in aqueous media studied by small-angle neutron scattering

Abstract

This article presents the characterization of two self-associated structures, a C(80)-tetraacid (also known as ARN), which is an aliphatic molecule present in crude oil and responsible for the formation of deposits, and BP-10, a molecule designed to model the properties of the C(80)-tetraacid. These molecules have four carboxylic functions at the end of four interconnected hydrocarbon chains and can be dissolved in aqueous solution and in basic media. In this paper we have used small-angle neutron scattering (SANS) as the main method to study the tetrameric acids in solution. SANS measurements show that the two molecules (in sodium form) exhibit very different types of aggregation properties in aqueous solution. More specifically, Na(4)BP-10 forms nanometer-sized micelles with an aggregation number close to 5 (at concentrations above the critical micellar concentration) in both 20 mM NaCl and 0.9 wt.% 1-butanol media. On the contrary fully ionised C(80)-TA forms very large structures in pure D(2)O and NaCl 20 mM, so large that their exact dimensions could not be determined by SANS.