Optorheological Studies of Sheared Confined Fluids with Mesoscopic Thickness. Soga, Iwao; Dhinojwala, Ali; Granick, Steve. Department of Materials Science and Engineering, University of Illinois, Urbana, IL, USA. Langmuir (1998), 14(5), 1156-1161. CODEN: LANGD5 ISSN: 0743-7463. Journal written in English. CAN 128:184908 AN 1998:95159 CAPLUS

Fluids of mesoscopic thickness can be sheared and their mol. orientation probed concurrently with the new instrument described in this paper. The fluid is confined between parallel optically flat windows whose spacing is controlled, using piezoelec. inchworms, from submicrometer thickness to .apprx.500 mm, with no essential lower limit apart from surface roughness. Capacitance sensors or optical interferometry is used to monitor spacing between the windows with submicrometer accuracy. Piezoelec. bimorphs are used to apply periodic shear displacements with amplitude 0.1-10 mm and frequency 0.1-700 Hz. Shear-induced mol. alignment during sinusoidal shear cycles is detd., with up to 5 ms time resoln., using step-scan time-resolved IR spectroscopy. To demonstrate capabilities of this new instrument, we describe an expt. in which shear and elec. fields were applied in orthogonal directions to 5-cyanobiphenyl (5CB), a simple nematic liq. crystal. Provided that the mol. lacked the time to relax during the period of oscillation, the mol. tilted back and forth around the equil. orientation under the action of small-amplitude oscillating shear. The shear alignment appeared to be proportional to the shear displacement, not to the effective shear rate.