SANS: a powerful tool to probe foams and emulsions

Foams and emulsions are complex out-of-equilibrium systems whose relevant structural length-scales span from a few nanometers up to millimeters. It is thus necessary to combine several techniques to obtain a refined description of their structure. In this lecture I will show how Small Angle Neutron Scattering can provide such a description at the nanometer scale, although this technique which is widely used in Soft Matter remains poorly used for probing foams and emulsions.

In a first time, I will show how the use of contrast variation enabled to describe the mechanism of stabilization of Pickering emulsions based on cellulose nanocrystals [1]. In a second part, I will discuss the different scattering events that occur when a foam is probed by SANS : the reflectivity from the thin films, which is the main process that occur in dry foams and the bulk scattering from the liquid in the Plateau border, which the main process that occur in wet foams [2]. I will then illustrate how SANS was use to unravel the outstanding properties of foams based either on 12-hydroxystearic fatty acids, the first ultrastable and thermos-responsive foams described in literature [3], or on Sodium Dodecyl Sulfate at high concentration [4].

[1] F. Cherhal, F. Cousin, I. Capron, Structural description of the interface of Pickering emulsions stabilized by cellulose nanocrystals, Biomacromolecules, 2016, 17(2), pp 496–502.

[2] A. Mikhailovskaya, L. Zhang, F. Cousin, F. Boué, P. Yazhgur, F. Muller, C. Gay, A. Salonen, Probing foam with neutrons, Adv. in Coll. and Int. Science, 2017, 247, 444-453.

[3] A.-L. Fameau, A. Saint-Jalmes, F. Cousin, F. Boué, B. Houinsou Houssou, L. Navailles, F. Nallet, C. Gaillard, B. Novales, J.-P. Douliez, Smart Foams: Switching Reversibly between Ultrastable and Unstable Foams, Angewandte Chemie Int. Ed., 2011, 50, 8264 –8269.

[4] L. Zhang, A. Mikhailovskaya1, P. Yazhgur, F. Muller, F. Cousin, D. Langevin, N. Wang, A. Salonen, Precipitating Sodium Dodecyl Sulfate to Create Ultrastable and Stimulable Foams, Angewandte Chemie Int. Ed., 2015, 127(33), 9669–9672.