Molecular dynamics simulations of poly(vinyl methyl ether) in aqueous solution with weight concentration c_w = 30% were performed in a wide temperature range by simulated cooling between 400 and 175 K. A shift of glass transition temperature due to plasticization effect is observed with the decrease of simulated T_g^MD by 25 K as compared to pure PVME at the same simulated cooling rate. The free volume is computed by using different probe radii (R_p). The free volume computed with R_p = 0.5 Å reproduces free volume amounts at the glass transition temperature from the free volume theories as well as thermal expansivity of the excess free volume given as α_L – α_G. A portion of 90% of the free volume is formed by molecular bodies of both polymer and water molecules. In the presence of water molecules, the free volume of polymer ends shows only a miniscule increase by 7% as compared to the free volume around main-chain monomer units. The free volume around hydrophilic polymer groups involved in hydrogen-bonding formation is decreased, in agreement with the predicted relation between mobility and free volume. A picture hinting why percolation of the free volume is naturally connected with glass transition temperature is provided. By using the computed free volumes, we predicted a value of the orthopositronium (o-Ps) lifetime in the structure to be τ₃ = 1.31 ns (40.1 ± 0.5 ų) in cavities formed solely by monomer units, and τ₃ = 2.03 ns for the average cavity in the structure.

中文翻译：

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PVME聚合物-水溶液中的自由体积

通过在400至175 K之间进行模拟冷却，在较宽的温度范围内对重量浓度为c _w = 30％的水溶液中的聚乙烯（乙烯基甲基醚）进行了分子动力学模拟。观察到由于增塑作用，玻璃化转变温度发生了变化。与纯PVME相比，在相同的模拟冷却速率下，模拟T _g ^MD降低了25K。通过使用不同的探针半径（R _p）计算自由体积。的自由体积与计算- [R _p = 0.5的再现给定为α在从自由体积的理论玻璃化转变温度的自由体积的量以及过量的自由体积的热膨胀_大号- α _ģ。90％的自由体积是由聚合物和水分子的分子体形成的。在水分子的存在下，聚合物末端的自由体积与主链单体单元周围的自由体积相比仅增加了7％。与氢键形成有关的亲水性聚合物基团周围的自由体积减少，这与迁移率和自由体积之间的预测关系一致。提供了图片，说明了为什么自由体积的渗滤与玻璃化转变温度自然相关。通过使用所计算的自由体积，我们在结构预测orthopositronium（邻- Ps）的寿命的值设定为τ ₃ = 1.31纳秒（40.1±0.5埃³）在空腔由单体单元单独形成的，和τ ₃ = 2.03纳秒用于该结构中的平均腔。