Small Angle (SANS) and Ultra-Small Angle Neutron Scattering (USANS) of Water-in-Oil Emulsions

V. Verruto and P. K. Kilpatrick

Department of Chemical and Biomolecular Engineering

North Carolina State University, Raleigh, NC USA  27695-7905

peter-k@ncsu.edu; 919-515-7121

There are few techniques that enable the careful characterization of the thin (order nanometers) films that stabilize water-in-oil emulsions.  In petroleum fluids, these films can be asphaltenic, or naphthenic acids and naphthenates, or a combination of these two.  We have probed these thin films by SANS and more recently by USANS.  By judiciously choosing the components of the disperse phase (hydrogenated and deuterated water) and those of the continuous phase (hydrogenated and deuterated oils), one can both contrast match and density-match the dispersed and continuous phases.  This then enables scattering experiments to be performed in which the information gleaned at very small scattering angle (large length scales) is dominated by the film’s composition and scattering length density.  It also enables experiments to be performed in which the dispersed phase volume fraction can be decreased to very small values.  We present our most recent results on emulsions stabilized by asphaltenes, carboxylic acids of the naphthenate type, and resins.  We also present the results of a polydisperse core-shell model of the scattering that enables sensitivity analyses and the selection of the optimal conditions from which to extract information on film thickness and composition.