Isothermal physical aging of thin PMMA films near the glass transition temperature |
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Authors: | Jung Eun Nam Jong Keun Lee Timothy C Mauldin |
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Affiliation: | 1. Department of Polymer Science and Engineering, Kumoh National Institute of Technology, Gumi, 730-701, Republic of Korea 3. Korea Institute of Materials Science, 531 Changwondaero, Changwon, Gyeongnam, 641-831, Korea 2. Department of Materials Science and Engineering, School of Engineering, Iowa State University, Ames, IA, 50011, USA
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Abstract: | Isothermal physical aging and the glass transition temperature (T
g) of PMMA thin films were investigated by means of differential scanning calorimetry (DSC). Freestanding thin films of different
molecular weights (M
w = 120,000, 350,000, 996,000 g/mol) and film thicknesses (40–667 nm) were obtained by spin coating onto a silicon wafer substrate
and then releasing the coated film using a water floating technique. The thin films were stacked in a DSC pan and isothermally
aged for different aging times (t
a = 1 and 12 h) and aging temperatures (T
a = 105, 110, and 115 °C) below but near T
g. Enthalpy relaxation (ΔH
Relax), resulting from the isothermal physical aging, initially increased with increasing ΔT (T
g − T
a, driving force of aging), reached a maximum value, and then decreased with further increase in ΔT. Below ~100 nm film thickness, ΔH
Relax of samples aged near their T
g (i.e., T
a = 110 and 115 °C) decreased with decreasing film thickness, indicating the suppression of physical aging. Up to 9.9 °C depression
in T
g was observed for thinner films (~40 nm), when compared to the thicker films (~660 nm) in this study. The decrease in ΔH
Relax with decreasing film thickness at a given T
a appears to be associated with the reduction in T
g. |
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Keywords: | |
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