Modified by Farrell Rogers from E. R. Waclawik, M. J. Ford,
P. S. Hale, J. G. Shapter, and N. H. Voelcker, "Liquid Crystal Displays:
Fabrication and Measurment of a Twisted Nematic Liquid-Crystal Cell," J.
Chem. Educ., 81,
854 (2004) and C. Liberko and J. Shearer,
"Preparation of a Surface-Oriented Liquid Crystal," J. Chem. Educ.,
77, 1204 (2000).
In this experiment a liquid crystal is oriented
between two polarizing filters. The transparency changes when a voltage is applied.
Dissolve polyvinyl alcohol in water, heating as necessary.
Use a hotplate to evaporate the polyvinyl alcohol solution onto
the conducting side of piece of FTO glass. Prepare two pieces.
Rub the PVA layer with a cotton cloth, maintaing the same direction
for each stroke.
Make sure one edge of the glass is free of PVA by wiping with a
damp tissue. The stroke orientation for the second piece should be perpendicular
to that of the first piece.
The glass should be coated with PVA except at one edge.
Cut two strips of plastic wrap. Using the plastic wrap as a spacer,
assemble offset glass squares with PVA on the inside and the uncoated
edge extending beyond the sandwich to allow an electrical connection
to each glass piece.
Clamp using binder clips.
Use capillary action to transfer the 4’-pentyl-4-biphenyl-carbonitrile liquid
crystal into a capillary tube.
Transfer liquid crystal from the capillary tube to the space between
the glass plates.
Obtain two polarizing filters. Crossed polarizers do
not transmit light.
Add crossed polarizers, one on each side, slipping them under the
Cycle the pixel on and off by connecting and disconnecting a 9V battery.
Graph %transmittance as a function of time
when the voltage is cycled on and off.