To design long-lived liquid crystal devices, it is important to unders
tand how liquid crystal properties change as the material degrades. Th
e liquid crystal 4'-octyl-4-cyanobiphenyl (8CB) is known to form well-
ordered, epitaxial monolayers on graphite. We have found that adding t
wo oxidation products (to mimic the effects of air oxidation or pyroly
sis) changes the surface ordering of 8CB, causing it to form monolayer
s on graphite which possess good short-range order but only moderate l
ong-range order, indicating the existence of many nonepitaxial domains
. Although the unit cell dimensions of domains within these monolayers
are identical to the unit cell dimensions of one of the oxidation pro
ducts, both pure oxidation products were found to form epitaxial monol
ayers on graphite, as did all binary mixtures of these materials. Thus
the loss of epitaxy seen in the 8CB mixtures is a consequence of inte
ractions between all three components (8CB and two oxidation products)
. The observed behavior of these 8CB mixtures is consistent with segre
gation of two components at domain walls separating domains of the pur
e third component.