کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
9694105 1459639 2005 5 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Gel-sol transition of poly(vinyl alcohol) hydrogels formed by freezing and thawing
موضوعات مرتبط
مهندسی و علوم پایه مهندسی شیمی جریان سیال و فرایندهای انتقال
پیش نمایش صفحه اول مقاله
Gel-sol transition of poly(vinyl alcohol) hydrogels formed by freezing and thawing
چکیده انگلیسی
Poly(vinyl alcohol) (PVA) hydrogels were prepared by freezing and thawing. Freezing and thawing cycle (n) was varied from 1 to 5. Gel-sol transition of the above hydrogels was measured using a highly sensitive differential scanning calorimeter (DSC). Phase transition of hydrogels was also investigated by simultaneous X-ray diffractometry (XRD) and DSC. Gel-sol transition temperature was observed in a temperature range from 55 to ca. 90 °C. Enthalpy of gel-sol transition was varied in a range from ca. 0.4 to 2 J g−1. Peak temperature and enthalpy of gel-sol transition increased with increasing n. By simultaneous measurement of X-ray diffractometry (XRD) and DSC, it is confirmed that no structural change is observed for either ice or water before and after gel formation. It is concluded that PVA molecules are aggregated during ice formation and hydrogen bonding is established between molecular chains. By increase of freezing and thawing cycle, residual free molecular chains are successively included in junction zones.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Thermochimica Acta - Volume 431, Issues 1–2, 15 June 2005, Pages 144-148
نویسندگان
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