Effects of shear flow on interfacial ordering in liquids: X-ray scattering studies

X-ray scattering was used to observe the effects of shear on the interfacial structures of two nonpolar/nonmetallic liquids. Unsheared tetrakis(2-ethylhexoxy)silane, a normal liquid with spherical molecules, is known to show a diffraction peak indicating the presence of approximately three layers at a solid-liquid interface. We find that the peak height drops with increasing shear rate but the peak width and position do not change, indicating a decrease in the interface area covered by the layers. With the chain-molecule liquid poly(dimethylsiloxane), where in static conditions no diffraction peak is seen, an interfacial peak appears under high shear rates - most likely because of chain disentanglement - and persists for ∼3 h after we stop applying shear.