ALIGNMENT OF COMPLEX FLUIDS UNDER CONFINEMENT AND FLOW

We report on a new application of the X-ray Surface Forces Apparatus [ 1-4] (XSFA) to the study of the alignment of complex fluid thin films under confinement and/or flow using synchrotron X-ray scattering. The smectic A liquid crystal 8CB (4-cyano-4'-octylbiphenyl) and the hexago nal phases of a zwitterionic polyisoprene melt and of a lyotropic liqu id crystal composed of sodium dodecyl sulfate (SDS), pentanol and wate r were investigated in the regime where the distances between the conf ining surfaces range from 0.4 to tens of microns. In this paper, we de monstrate that this new technique allows preparation of highly-oriente d complex fluid samples suitable for high resolution X-ray diffraction and scattering studies. In addition, we have directly measured forces across thin films of 8CB using the conventional Surface Forces Appara tus (SFA). The force measurements complement well the direct X-ray ima ging and provide indirect information on the sample alignment in films a few tens of Angstroms thick.