کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
2488122 | 1114459 | 2006 | 16 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Dynamic Heat Capacity and Relaxation Time of Ultraviscous Melt and Glassy Acetaminophen
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موضوعات مرتبط
علوم پزشکی و سلامت
داروسازی، سم شناسی و علوم دارویی
اکتشاف دارویی
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چکیده انگلیسی
The real and imaginary components, Câ²p and Câ³p, of the complex heat capacity, Cpâ²=Câ²pâiCâ³p of supercooled, ultraviscous melt of acetaminophen have been measured at different temperatures during cooling through its vitrification range and during heating through its glass-softening range by using a modulation frequency of 3.3 mHz. From these data, the distribution of relaxation time parameter, β, and a characteristic (calorimetric or configurational) relaxation time, Ïcal, have been determined. A constant value of 0.65 for β fits the data, and Ïcal varies with the temperature according to the Vogel-Fulcher-Tammann equation, Ïcal = 10â12.95 exp[1813/(T â 240.5)]. This relation differs significantly from the one deduced by others in which the configurational entropy theory was used to deduce Ïcal. The Câ²p and Câ³p values measured during the cooling of its ultraviscous melt and during the heating of its glassy state show a small hysteresis only at low temperatures. These investigations also provide a comparison of calorimetric and dielectric relaxation times in ultraviscous acetaminophen and highlight the role of faster modes of relaxation at low temperatures in organic, molecular glasses that can help in a better understanding of the crystal nucleation process in glasses at T below their Tg.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Journal of Pharmaceutical Sciences - Volume 95, Issue 5, May 2006, Pages 1006-1021
Journal: Journal of Pharmaceutical Sciences - Volume 95, Issue 5, May 2006, Pages 1006-1021
نویسندگان
E. Tombari, S. Presto, G.P. Johari, Ravi M. Shanker,