Direct measurement of fluid mechanical properties in micro space: Liquid crystal orientation under sheer

The sheer-induced molecular orientation of a nematic liquid crystal, 5CB (4 -pentyl-4'-cyanobiphenyl) was studied ill a newly-developed apparatus in wh ich the liquid crystal was confined between optical windows at a film thick ness that is continuously variable. The molecular orientation was measured in situ during shear in the presence and absence of DC electrical bias betw een the two surfaces. In this preliminary study we present findings for a s pacing of 10 mu m, which is comparable to the spacing of actual liquid crys tal display technology Fourier transform infrared time resolved spectroscop y (FTIR-TRS) synchronized with the shear motion provided the molecular orie ntation as a function of time during the shear cycle. Only a slight orienta tion along the shear direction was found in the isotropic state but, in the homeotropic state, the molecular orientations in response to shear reflect ed a competition process between orientation in orthogonal directions. Shea r promoted orientation parallel to the confining plates, and a DC bias volt age promoted orientation perpendicular to the confining plates.