当前位置： SCI文献检索 > PHARMACEUTICAL RESEARCH期刊下所有文献 > Distribution and effect of water content on molecular mobility in poly(vinylpyrrolidone) glasses: a molecular dynamics simulation.

Distribution and effect of water content on molecular mobility in poly(vinylpyrrolidone) glasses: a molecular dynamics simulation.

Abstract：

PURPOSE:This work explores the distribution of water and its effects on molecular mobilities in poly(vinylpyrrolidone) (PVP) glasses using molecular dynamics (MD) simulation technology. METHODS: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 micros by MD simulation. RESULTS:Increasing water content from 0.5% to 10% w/w was found to reduce the Tg 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. CONCLUSIONS: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.

journal_name

Pharm Res

journal_title

Pharmaceutical research

authors

Xiang TX,Anderson BD

doi

10.1007/s11095-005-5277-5

subject

Has Abstract

pub_date

2005-08-01 00:00:00

pages

1205-14

issue

eissn

0724-8741

issn

1573-904X

journal_volume

pub_type

杂志文章

在线工具

Distribution and effect of water content on molecular mobility in poly(vinylpyrrolidone) glasses: a molecular dynamics simulation.