کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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5186431 | 1381104 | 2009 | 12 صفحه PDF | دانلود رایگان |
Interfacial interactions/dynamics were studied in silica core-poly(vinyl pyrrolidone) (PVP) shell nanoparticles with the shell thickness of 1-2 (monolayer), 2-5, 5-15, and 8-25 nm using far- and mid-IR spectroscopy and DSC activation analysis of the glass transition. Particles were prepared using a pseudo-liquid state procedure. Their geometry, structural organization and shell uniformity were characterized comprehensively by LTNA, AFM, QELS, FT-IR and densitometry techniques. As revealed, strong core-shell interfacial interactions, including hydrogen bonding and Lewis acid-base ones, resulted in the quite different, multi-modal glass transition dynamics in PVP nano shells. For 1-2 nm thick monomolecular PVP shell, only several “abnormal” modes, including constrained cooperative and non-cooperative as well as ultra-fast non-cooperative ones, constituted segmental dynamics in the glass transition; the latter covered the range from 70 to 230 °C, with varying apparent activation energy by one order of magnitude. Ultra-fast dynamic mode was caused by collapse of motional cooperativity (α- to β-relaxation transformation).
Journal: Polymer - Volume 50, Issue 3, 28 January 2009, Pages 860-871