SESANS DETECTS COLLOIDAL JAMMING IN NANOCONFINEMENTS

Rana Ashkar and Roger Pynn

 

The assembly of matter in nano-confinements is emerging as a low-cost candidate for fabricating controlled highly-ordered nanomaterials. To understand this behavior a 3D structural characterization of the confined matter is necessary. On one hand, nondestructive probing of such samples challenges conventional microscopy techniques. On the other hand, the submicron size of a single confinement is impractical for neutron and x-ray scattering experiments but this dilemma can be overcome by using a confining matrix made up of an array of identical confinements such as the channels of a diffraction grating. The caveat is that the periodicity of the matrix amplifies dynamical scattering effects that are not accounted for in approximate scattering theories and a full dynamical theory (DT) calculation becomes unavoidable. A dynamical theory model we have recently developed gives good account of spin-echo small angle neutron scattering (SESANS) data on nanostructured gratings. Unlike traditional diffraction techniques that require collecting a large number of diffraction orders to deduce the structure of materials, SESANS overcomes this problem by measuring density correlations in real space. In addition, the technique allows neutron scattering to access the length scales of interest which lie in the few-tens-of-nanometers to several-micron range. The combination of SESANS measurements and DT calculations on a semi dilute silica suspension in contact with a nanopatterned grating shows jamming of the colloidal particles in the grating channels.