Molecular Orientation in Stable Glasses of Indomethacin.

Spectroscopic ellipsometry has been used to measure the properties of indomethacin prepared by physical vapor deposition at Tsubstrate/Tg = 0.78, 0.84, and 0.90. The as-deposited glasses exhibited high kinetic stability and had densities 0.8-1.2% higher than the ordinary glass prepared by cooling the liquid at 1 K/min. Deposition at the higher temperatures yielded glasses with positive birefringence (up to Δn = 0.028), while the lowest-temperature sample was negatively birefringent (Δn = -0.015). These results indicate that substrate temperature can be used to manipulate molecular orientation in high-density and high-stability glasses. The data for the supercooled liquid and the ordinary glass of indomethacin are reasonably consistent with the Lorentz-Lorenz equation, but significant deviations are noted with the as-deposited materials.