Rotational manipulation and stacking of nanosystems.
In this paper two kinds of Bragg reflections from oriented mesogenic crystals are considered. Bragg reflections behave differently for ...ABABA... and ...ABCABCA... layer stacking. We call them black and white reflections. Black reflections are characterized by the fact that they behave identical for the two kinds of stacking. Therefore, the message is the following: Black rods should not be used to identify the two kinds of stacking. By contrast, white reflections show a different behavior for ...ABABA... and ...ABCABCA... stacking and for the resulting hexagonal close-packed (hcp) and face-centered cubic (fcc) crystals. White reflections can be used to distinguish the two kinds of crystals. For an application of this method the crystals should be oriented. It will be shown that orienting by flow is possible in a Couette cell. Flow ordering occurs in all rotation cells which are often applied in rheology. The scattering presented is therefore closely related to rheology. Details and experimental results will be given in the paper.
Versmold
Heiner
H
Institut für Physikalische Chemie der RWTH, D-52052 Aachen, Germany. versmold@pc.rwth-aachen.de