The mechanism of light gas transport through configurational free volume in glassy polymers
The mechanism of light gas transport through configurational free volume in glassy polymers
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DOI：
10.1016/j.memsci.2022.120608
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发表时间：
2022-05-24
影响因子：
9.5
通讯作者：
Galizia, Michele
中科院分区：
文献类型：
--
作者：
Box, William J.;Huang, Zihan;Galizia, Michele
提出了包含构型自由体积（即三蝶烯部分）的玻璃状聚合物膜中小分子运输的可能机制。为此，选择了一系列含有三蝶烯的聚苯并恶唑 (TPBO)，其三蝶烯单元的摩尔量在 25% 至 100% 范围内系统变化，用于进行轻质气体（N-2、CH4 和 CO2）基本吸附传输研究。双模式吸附迁移率模型用于分离构型自由体积对渗透剂传输的影响。 CO2 和 CH4 Henry 和 Langmuir 模式扩散系数被估计并用于量化 Henry 和 Langmuir 对 CO2/CH4 扩散选择性的贡献，作为 TPBO 中三蝶烯摩尔含量的函数。有趣的是，虽然 Henry 的 CO2/CH4 扩散率-选择性随着构型自由体积的增加而变化很小，但当聚合物中三蝶烯摩尔浓度为 75% 或更高时，Langmuir 的 CO2/CH4 扩散率-选择性增加到无穷大，这表明当更多的构型自由体积纳入聚合物中时，较大分子（即 CH4）的扩散相对于较小分子（即 CO2）的扩散越来越受到阻碍。聚合物。与此形成鲜明对比的是，纯气体和混合气体吸附以及溶解度选择性基本上不受三蝶烯摩尔含量的影响。根据该物理图，CO2吸附等量热分析表明TPBOs的塑化阻力与三苯乙烯含量无关。
A possible mechanism of small molecule transport in glassy polymer membranes containing configurational free volume (i.e., triptycene moieties) is proposed. To this aim, a family of triptycene-containing polybenzoxazoles (TPBOs) exhibiting systematically varied molar amount of triptycene units, ranging from 25% to 100%, was selected to perform a light gas (N-2, CH4 and CO2) fundamental sorption-transport study. The dual mode sorption-mobility model was used to isolate the effect of configurational free volume on penetrant transport. CO2 and CH4 Henry's and Langmuir's mode diffusion coefficients were estimated and used to quantify the Henry's and Langmuir's contributions to CO2/CH4 diffusivity-selectivity as a function of the triptycene molar content in TPBOs. Interestingly, while the Henry's CO2/CH4 diffusivity-selectivity changes little with increasing amount of configurational free volume, the Langmuir's CO2/CH4 diffusivity-selectivity increases up to infinity when the molar triptycene concentration in the polymer is 75% or higher, showing that the diffusion of larger molecules (i. e., CH4) is increasingly hindered relative to smaller molecules (i.e. CO2) diffusion when more configurational free volume is incorporated in the polymer. In sharp contrast, pure-and mixed-gas sorption, as well as solubility-selectivity, is essentially unaffected by the triptycene molar content. According with this physical picture, the analysis of isosteric heats of CO2 sorption indicates that TPBOs plasticization resistance is independent of trip-tycene content.