  We present the results of molecular dynamics simulations of odd alkane
impurities present within the hexane (even alkane) monolayer. We simulate
various temperatures at ca. 3%, 5%, 10%, and 15% impurities of propane,
pentane, heptane, nonane, and undecane, each having a low-temperature solid
phase belonging to a different space group as compared to hexane, to study the
effects of impurities on the various phases and phase transitions for hexane
monolayers that are well-characterized through previous experimental and
theoretical work. Based upon preferential adsorption, we provide two emerging
pictures of how impurities could affect the monolayer, for impurity chain
lengths longer and shorter than that of the hexane molecules. We provide
evidence that impurities in the monolayer, even in small proportion to the
hexane, could induce significant changes in the phase behavior and phase
transitions, and we propose that because of the size of pentane with respect to
hexane, and the nature of the solid herringbone phase, pentane impurities give
the best representation of the phase behavior observed for the pure hexane
monolayer. We find that impurities with chain lengths longer than hexane tend
to distort the sublattices of the solid herringbone phase, and hence lead to a
phase transition into an intermediate phase significantly prior to that
observed for a pure hexane monolayer. We discuss an interpretation of this
study that could be potentially useful for future experimental work.
