Comparative Study of Different Probing Techniques for the Analysis of the Free Volume Distribution in Amorphous Glassy Perfluoropolymers
Comparative Study of Different Probing Techniques for the Analysis of the Free Volume Distribution in Amorphous Glassy Perfluoropolymers
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DOI：
10.1021/ma901244d
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发表时间：
2009-10-13
期刊：
影响因子：
5.5
通讯作者：
Drioli, Enrico
中科院分区：
文献类型：
--
作者：
Jansen, Johannes C.;Macchione, Marialuigia;Drioli, Enrico
五种不同的实验和计算方法的比较研究的整体自由体积（FV）和自由体积元（FVE）的大小和形状分布在无定形玻璃态全氟聚合物（PFPs）的表征。实验结果从光致变色探针（PCP）的方法，正电子湮没寿命谱（帕尔斯），和反气相色谱（IGC）面临的文献数据从129 NMR光谱，和实验数据进行了进一步比较，与分子动力学（MD）模拟和MD研究和著名的Bondi方法，以及修改后的Bondi方法相结合。每种方法的优点和局限性的评价。这是第一次报道的研究，如此大量的互补技术应用于一个单一的玻璃状聚合物，在这种情况下，HYPERAND AD全氟聚合物，也是第一次成功的应用光致变色探针技术在这种材料。在两种不同等级的Hypersonic AD中，发现具有最高含量的刚性环状共聚单体的聚合物具有稍大的平均FVE尺寸，但具有较低的空隙浓度，这解释了两种样品的几乎相同的密度和自由体积分数（FFV）。此外，帕尔斯证明了与熔融压制样品相比，溶液浇铸样品的类似趋势，后者具有较小尺寸但较高浓度的FVE。IGC的数据似乎与PCP方法的数据最为接近。来自各个技术的结果之间的差异主要来自于各种探测方法的根本不同的性质，但也来自于考虑FVE形状的不同能力。只有分子动力学模拟研究，使用详细的原子包装模型，可以直接深入了解FVE的空间排列。除了提供最高水平的细节，MD模拟因此可以帮助理解实验方法的可能限制。它们的自由体积分布的知识是至关重要的，以获得更多的洞察这些材料中的传质现象，相关的成功应用在新兴领域的合成膜的气体和蒸汽分离。
A comparative study of five different experimental and computational methods is presented for the characterization of the overall free volume (FV) and the free volume element (FVE) size and shape distribution in amorphous glassy perfluoropolymers (PFPs). Experimental results from the photochromic probe (PCP) method, positron annihilation lifetime spectroscopy (PALS), and inverse gas chromatography (IGC) were confronted with literature data from Xe-129 NMR spectroscopy, and the experimental data were further compared with molecular dynamics (MD) simulations and a combination of MD studies and the well-known Bondi method as well as a modified Bondi method. An evaluation of the advantages and the limits of each method is presented. This is the first reported study on a so vast number of complementary techniques applied on a single glassy polymer, in this case Hyflon AD perfluoropolymer, and is also the first successful application of the photochromic probe technique in such materials. In two different grades of Hyflon AD, the polymer with the highest content of the stiff cyclic comonomer was found to have a slightly larger average FVE size but a lower void concentration, explaining the nearly identical density and fractional free volume (FFV) of the two samples. PALS furthermore demonstrated a similar trend for solution-cast samples in comparison with melt-pressed samples, the latter having FVEs with a smaller size but a higher concentration. The data from IGC seem to correspond most closely to those of the PCP method. Differences between the results from the individual techniques derive mainly from the fundamentally diverse nature of the various probing methods but also from the different capacity to take into account the FVE shape. Only MD Simulation studies, using detailed atomistic packing models, can give such deep insight into the spatial arrangement of the FVEs directly. Besides giving the highest level of detail, MD simulations can thus help to understand the possible limits of the experimental methods. Knowledge of their free volume distribution is of fundamental importance to gain more insight into the mass transport phenomena in these materials, relevant for their successful application in the emerging Field of synthetic membranes for gas and vapor separations.