Liquids under shear
Neutron reflectrometry experiments have shown that sheared polymer solutions exhibit distinct wetting behaviour on coated silicon wafers and characteristic structural changes in the bulk.
The intensity maps (see figure) reproduce the specular and off-specular reflectivity of P85 molecules dissolved in heavy water under shear, which are placed in between hydrophobic and hydrophilic Si discs.
Without shear a Bragg sheet is visible for the hydrophilic interface, which becomes more pronounced under shear, indicative for an ordering and layering of the liquid. In contrast, only a weak Bragg sheet is visible for the hydrophobic interface, which becomes even weaker under shear.
This is an impressive demonstration of how liquid ordering depends on the nature of the solid – liquid interface.
(Courtesy of M. Wolff).