Observation of low heat capacities for vapor-deposited glasses of indomethacin as determined by AC nanocalorimetry

Journal Article · Wed Jul 07 00:00:00 EDT 2010 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.3442416· OSTI ID:21559877

Kearns, Kenneth L; Whitaker, Katherine R; Ediger, M D ^[1]; Huth, Heiko; Schick, Christoph ^[2]

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1. Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
2. Institute of Physics, University of Rostock, Rostock 18051 (Germany)

Highly stable glass films of indomethacin (IMC) with thicknesses ranging from 75 to 2900 nm were prepared by physical vapor deposition. Alternating current (AC) nanocalorimetry was used to evaluate the heat capacity and kinetic stability of the glasses as a function of thickness. Glasses deposited at a substrate temperature of 0.84T{sub g} displayed heat capacities that were approximately 19 J/(mol K) (4.5%) lower than glasses deposited at T{sub g} (315 K) or the ordinary glass prepared by cooling the liquid. This difference in heat capacity was observed over the entire thickness range and is significantly larger than the {approx}2 J/(mol K) (0.3%) difference previously observed between aged and ordinary glasses. The vapor-deposited glasses were isothermally transformed into the supercooled liquid above T{sub g}. Glasses with low heat capacities exhibited high kinetic stability. The transformation time increased by an order of magnitude as the film thickness increased from 75 to 600 nm and was independent of film thickness for the thickest films. We interpret these results to indicate that the transformation of stable glass into supercooled liquid can occur by either a surface-initiated or bulk mechanism. In these experiments, the structural relaxation time of the IMC supercooled liquid was observed to be nearly independent of sample thickness.

• OSTI ID: 21559877
• Journal Information: Journal of Chemical Physics, Vol. 133, Issue 1; Other Information: DOI: 10.1063/1.3442416; (c) 2010 American Institute of Physics; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
AGING
ALTERNATING CURRENT
CALORIMETRY
FILMS
GLASS
LIQUIDS
NANOSTRUCTURES
ORGANIC COMPOUNDS
PHASE TRANSFORMATIONS
PHYSICAL VAPOR DEPOSITION
RELAXATION TIME
SOLIDS
SPECIFIC HEAT
STABILITY
SUBSTRATES
THICKNESS
TRANSFORMATIONS
TRANSITION HEAT
VAPOR DEPOSITED COATINGS
VAPORS
COATINGS
CURRENTS
DEPOSITION
DIMENSIONS
ELECTRIC CURRENTS
ENTHALPY
FLUIDS
GASES
PHYSICAL PROPERTIES
SURFACE COATING
THERMODYNAMIC PROPERTIES