Molecular spring as the driving force of cellulose and wood swelling
セルロースおよび木材膨潤の原動力としての分子バネ
Résumé
Dry cellulose and wood undergo exothermal swelling by water, which is problematic for
conventional material but also confers potential for actuating material. In the early 20th century, colloid chemists established the potential work of such swelling, which attains the order of kiloJoules per kg dry material, experimentally and theoretically. The origin of this swelling is not due to sorption sites or strong interaction between water and cellulose. Instead, semi-rigid polymers such as cellulose store internal energy as conformational energy during the drying as they reduce the surface energy. Sorption would reduce the surface energy, allowing the release of some of this stored internal energy to exert the swelling pressure. The conversion between surface energy and
internal stress depends on the spatial arrangement of molecules, which is crucial in controlling the swelling behavior of cellulosic materials.
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