Department of Chemistry, Polymer & Materials Chemistry, Lund University, Box 124, SE-2210 Lund, Sweden.
J Chem Phys. 2012 Jun 28;136(24):244902. doi: 10.1063/1.4729561.
The possibility of positronium induced free volume cavity expansion in some polymers above the glass transition temperature was investigated using experimental positron annihilation lifetime data from the literature for polydimethylsiloxane, polyisobutylene, and polybutadiene as function of temperature. The results suggest that free volume sites can expand towards an equilibrium size, determined as the equilibrium Ps-bubble size defined earlier for low-molecular-weight liquids. The expansion can be explained by the increase of molecular mobility and hence decrease of relaxation times, which at the higher temperatures approach the o-Ps lifetimes. Nanoscale viscosities were estimated using Navier-Stokes equation and were found to be several orders of magnitude lower than the macroscopic viscosity at the same temperature.
研究了聚二甲基硅氧烷、聚异丁烯和聚丁二烯在玻璃化转变温度以上的正电子素诱导自由体积空穴膨胀的可能性，使用文献中实验正电子湮没寿命数据作为温度的函数。结果表明，自由体积可以向平衡尺寸扩展，平衡 Ps 泡的尺寸可以由先前定义的低分子量液体来确定。这种膨胀可以用分子迁移率的增加来解释，因此弛豫时间减小，在较高温度下接近 o-Ps 寿命。使用纳维-斯托克斯方程估计了纳米级粘度，发现其在相同温度下比宏观粘度低几个数量级。
