Proposal of a New Liquid Separation Method Using Sub-Nanopores ―Separation of Alkanes with Different Chain Lengths Using the Internal Pores of Polyolefin Crystal―
January 15, 2020 Keio University Kyushu University
Assistant Professor Ayano Chiba of the Keio University Faculty of Science and Associate Professor Ryo Akiyama and Akio Oshima (graduate school student; completed master's program in 2019) of the Kyushu University Faculty of Science discovered a liquid separation method that makes use of crystalline polyolefin film and proposed a theory on its mechanism. In general, liquid separation refers to the extraction of specific molecules from a mixture containing multiple types of molecules. In liquid separation using a conventional porous film, a strategy of only allowing molecules smaller than the pores to pass through is employed. In this study, however, it was revealed that there is a strong tendency for large molecules to selectively enter a porous medium in a liquid mixture. This can be explained by a statistical mechanics theory called the Asakura-Oosawa model. In fact, when a crystalline film made of polyolefin called isotactic poly(4-methyl-1-pentene) was immersed in a binary mixture of normal (straight-chain) alkanes, the longer of the normal alkanes were selectively absorbed by the pores in the crystal. This can be thought to be a spontaneous liquid separation due to molecular volume. Of the conventional separation methods based on volume, a method called gel permeation chromatography (GPC), which separates macromolecules based on the degree of polymerization, that is, the effective volume, is well known. This study provides a new perspective on separating low-mass molecules by their volume.
The outcomes of this research were published in the online version of the American scientific journal "Langmuir" on November 18 (Mon.), 2019 (US time), ahead of its publication in the printed version of the same journal.
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