Anomalous Phenomena Occurring during Permeation and Sorption of C1-C6 Alcohol Vapors in Teflon AF 2400
Anomalous Phenomena Occurring during Permeation and Sorption of C1-C6 Alcohol Vapors in Teflon AF 2400
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DOI：
10.1021/ie303013y
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发表时间：
2013-08-07
影响因子：
4.2
通讯作者：
Drioli, Enrico
中科院分区：
文献类型：
--
作者：
Friess, Karel;Jansen, Johannes C.;Drioli, Enrico
本文报道了 C-1-C-6 醇蒸气在高自由体积、无定形玻璃状全氟聚合物 Teflon AF 2400 中的异常扩散。在这种材料中，在时间滞后测量期间，脂肪醇的压力增加曲线的瞬态表现出非常不寻常的行为，与之前报道的永久气体和其他蒸气（例如碳氢化合物、丙酮、二氯甲烷等）的扩散不同。这种不寻常的行为可以通过动态分子聚集体的同时扩散来解释：由至少两个或三个具有不同扩散系数的分子组成的簇，其数量级与单个分子的扩散系数不同。 C-1-C-6 醇蒸汽活性越高，簇形成的可能性就越大。此外，随着分子尺寸的增加，从甲醇到戊醇的平均簇尺寸减小，因为烃链更长，因此极性更低。 Teflon AF 2400 中的弱（丁醇、戊醇）和几乎为零（己醇）的聚类能力通过 ENSIC 模型以及通过蒸气活度范围 (0.15-0.95) 内的重力吸附实验的扩散评估独立得到证实。此外，我们提出了一种处理由配备校准石英（麦克贝恩）螺旋天平的重力吸附装置记录的原始吸附动力学数据的新方法。上述处理可以消除螺旋天平的重叠机械振荡（由样品气体/蒸汽初始充入真空测量室引起），并成功重建由气体/蒸汽吸附到聚合物材料中引起的螺旋的真实伸长。这使得即使从高噪声吸附数据中也能计算出气体/蒸汽扩散系数的准确值。
This paper reports on the anomalous diffusion of C-1-C-6 alcohol vapors in the high-free-volume, amorphous glassy perfluoropolymer Teflon AF 2400. In this material, during time lag measurements, the transient in the pressure increase curve of aliphatic alcohols exhibits a quite unusual behavior, different from the previously reported diffusion of permanent gases and that of other vapors (such as hydrocarbons, acetone, dichloromethane, etc.). Such unusual behavior can be explained by the simultaneous diffusion of dynamic molecular aggregates: clusters, made of at least two or three molecules with different diffusion coefficients, differing in orders of magnitude from those of single molecules. The probability of cluster formation increases at higher C-1-C-6 alcohol vapor activities. Moreover, the average cluster size decreases from methanol to pentanol with increasing molecular size, because of the longer hydrocarbon chain and, consequently, the lower polarity. Weak (butanol, pentanol) and almost zero (hexanol) clustering ability in Teflon AF 2400 was confirmed independently by the ENSIC model and through evaluation of diffusion from gravimetric sorption experiments in the vapor activity range (0.15-0.95). In addition, we present a novel method for the treatment of raw sorption kinetic data recorded by a gravimetric sorption apparatus equipped with a calibrated quartz (McBain's) spiral balance. The mentioned treatment allows one to eliminate overlapping mechanical oscillations of the spiral balance (caused by the initial charging of the sample gas/vapor into the evacuated measuring chamber) and successfully reconstruct the real elongation of the spiral caused by gas/vapor sorption into a polymer material. This allows to calculate accurate values of the gas/vapor diffusion coefficients, even from highly noisy sorption data.