Study of flow in a smectic liquid crystal in the X-ray Surface Forces Apparatus

Abstract

We describe the newly invented X-ray Surface Forces Apparatus (X-SFA) which allows the simultaneous measurement of forces and collective structures of confined complex fluids under static and flow conditions. The structure of the smectic liquid crystal 8CB (4-cyano-4{prime}-octylbiphenyl) confined between two mica surfaces with separation ranging from 4000 to 20,000 {angstrom} was measured. At small gaps and no shear, the smectic layers take on distinct stable orientations, including the bulk forbidden {open_quotes}b{close_quotes} orientation, which persist under low shear ({dot {gamma}} {<=} 30 s{sup -1}). However, at higher shear rates ({dot {gamma}} = 360 s{sup -1}), the shear acts to dramatically order and align the smectic layers into a single {open_quotes}a{close_quotes} orientation.