期刊
JOURNAL OF PHYSICAL CHEMISTRY B
卷 119, 期 15, 页码 5071-5078出版社
AMER CHEMICAL SOC
DOI: 10.1021/jp5127464
关键词
-
资金
- NSF [DMR-1206724]
Surface self-diffusion coefficients have been measured for the model molecular glass o-terphenyl (OTP) through surface-grating decay driven by capillarity. The decay mechanism transitions from viscous flow at high temperatures to surface diffusion at low temperatures; for 1000 nm wavelength gratings, the transition occurs at T-g + 11 K. The surface diffusion of OTP is 10(8) times faster than bulk diffusion at T-g and even faster at lower temperatures because of its weaker temperature dependence. At T-g, OTP has approximately the same bulk diffusivity as the previously studied molecular liquid indomethacin, but its surface diffusion is 100 times faster. While the molecular glass-formers exhibit transitions from viscous flow to surface diffusion as the mechanism of capillarity-driven surface flattening, polystyrenes and silicates show no such transition under comparable conditions, suggesting slower surface diffusion on these materials and a general dependence of surface diffusion on intermolecular forces. The velocity of surface crystal growth on molecular glasses is proportional to surface diffusivity, indicating a common kinetic barrier for both processes for temperatures below T-g.
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