Confined Space Enables Spontaneous Liquid Separation by Molecular Size: Selective Absorption of Alkanes into a Polyolefin Cast Film
Confined Space Enables Spontaneous Liquid Separation by Molecular Size: Selective Absorption of Alkanes into a Polyolefin Cast Film
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DOI：
10.1021/acs.langmuir.9b02509
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发表时间：
2019-12-31
期刊：
影响因子：
3.9
通讯作者：
Akiyama, Ryo
中科院分区：
文献类型：
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作者：
Chiba, Ayano;Oshima, Akio;Akiyama, Ryo
耗尽力已被用来解释胶体系统中的相分离现象。在这里，我们表明，耗尽力不仅可以解释大胶体颗粒和小胶体颗粒的相分离，还可以解释从液态大分子和小分子混合物中优先吸收较大分子的现象。当聚烯烃流延膜浸入长链和短链正烷烃的混合物中时，较长的分子被选择性地吸收到膜中。该实验结果是从耗尽力的角度进行解释的。主要发现是利用有限空间来强调由力引起的分离趋势。一般来说，熵的增加可以作为混合分子的驱动力。然而，如果存在足够窄的孔，随着熵的增加，大分子和小分子会根据尺寸自然分离。这一发现将导致低质量分子的尺寸排阻色谱法，类似于大分子的凝胶渗透色谱法。为了证明耗尽力的影响，我们选择并实验了基于聚烯烃全同立构聚（4-甲基-1-戊烯）（P4MP1）薄膜和正构烷烃混合物的体系，并实现了高分子选择性。我们使用的 P4MP1 薄膜只需从溶液中蒸发溶剂并流延薄膜即可制备。基于Asakura-Oosawa理论，我们得出结论，自发的高分子选择性归因于薄膜中尺寸均匀的小亚纳米孔提供的耗尽力。
The depletion force has been used to explain phase separation phenomena in colloidal systems. Here, we showed that depletion force can explain not only phase separation of large and small colloidal particles but also preferential absorption of larger molecules from a mixture of large and small molecules in a liquid state. When a polyolefin cast film was immersed in a mixture of long and short normal alkanes, the longer molecules were selectively absorbed into the film. This experimental result was explained from the viewpoint of depletion force. The main finding was the use of confined space to emphasize the separation tendency caused by the force. In general, the increase in entropy may serve as a driving force to mix molecules. However, if sufficiently narrow pores are present, large and small molecules are separated naturally by size as the entropy increases. This finding will lead to size exclusion chromatography of low-mass molecules, similar to gel permeation chromatography of macromolecules. In order to demonstrate the effect of depletion force, we selected and experimented with a system based on a polyolefin isotactic poly(4-methyl-1-pentene) (P4MP1) film and a normal alkane mixture and realized high molecular selectivity. The P4MP1 film we used can be prepared simply by evaporating the solvent from the solution and casting the film. On the basis of the Asakura-Oosawa theory, we concluded that spontaneous and high molecular selectivity is attributed to the depletion force provided by the small sub-nanopores with uniform size in the film.