  X-ray diffraction patterns of ethanol confined in parallel-aligned channels
of approx. 10 nm diameter and 50 micrometer length in mesoporous silicon have
been recorded as a function of filling fraction, temperature and for varying
cooling and heating rates. A sorption isotherm, recorded in the liquid state,
indicates a three monolayer thick, strongly adsorbed wall layer and a capillary
condensed fraction of molecules in the pore center. Though the strongly
adsorbed film remains in an amorphous state for the entire temperature range
investigated, the capillary condensed molecules reproduce the polymorphism of
bulk solid ethanol, that is the formation of either crystalline or glass-like
states as a function of cooling rate. The critical rate necessary to achieve a
vitrification in the mesopores is, however, at least two orders of magnitude
smaller than in the bulk state. This finding can be traced both to pure
geometrical constraints and quenched disorder effects, characteristic of
confinement in mesoporous silicon.
