NDLI: Distribution and Effect of Water Content on Molecular Mobility in Poly(vinylpyrrolidone) Glasses: A Molecular Dynamics Simulation

Content Provider	SpringerLink
Author	Xiang, Tian Xiang Anderson, Bradley D.
Copyright Year	2005
Abstract	This work explores the distribution of water and its effects on molecular mobilities in poly(vinylpyrrolidone) (PVP) glasses using molecular dynamics (MD) simulation technology.PVP glasses containing 0.5% and 10% w/w water and a small amount of ammonia and Phe-Asn-Gly were generated. Physical aging processes and associated structural and dynamic properties were monitored vs. time for periods up to 0.1 μs by MD simulation.Increasing water content from 0.5% to 10% w/w was found to reduce the T$_{g}$ by about 90 K and increase the rates of volume and enthalpy relaxation. At 0.5% w/w, water molecules are mostly isolated and uniformly distributed while at 10% w/w, water distribution is markedly heterogeneous, with strands of water molecules occupying channels between the polymer chains. At 10% w/w, each water molecule has an average of 2.0 neighboring water molecules. The plasticization effects of water were revealed in diffusion coefficient increases of 3.7-, 7.3-, and 7.6-fold for water, ammonia, and the individual polyvinylpyrrolidone segments, respectively, and in shorter relaxation times (37- to 47-fold) for rotation of polymer segments with an elevation in water content from 0.5% to 10% w/w. Water diffusivity was found to linearly correlate with the number of neighboring water molecules. Rotation of the PVP segments is comprised of a fast wobble motion within a highly restrained cavity and a slow rotation over a wider angular space. Only the slow rotation was shown to be significantly affected by water content.Water distribution in the PVP glass is highly heterogeneous at 10% w/w water, reflecting the formation of water strands or small clusters rather than complete phase separation. Local enhancement of mobility with increasing water content has been demonstrated using MD simulations.
Starting Page	1205
Ending Page	1214
Page Count	10
File Format	PDF
ISSN	07248741
Journal	Pharmaceutical Research
Volume Number	22
Issue Number	8
e-ISSN	1573904X
Language	English
Publisher	Springer-Verlag
Publisher Date	2005-08-03
Publisher Place	New York
Access Restriction	Subscribed
Subject Keyword	amorphous polymers diffusion molecular dynamics simulation molecular mobility PVP solid-state stability water uptake Pharmacology/Toxicology Pharmacy Biochemistry Medical Law Biomedical Engineering
Content Type	Text
Resource Type	Article
Subject	Pharmaceutical Science Pharmacology (medical) Molecular Medicine Biotechnology Pharmacology Organic Chemistry

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