Jun 12, 2020 | |
Vapor-sensitive materials with self-assembling twisted microstructure(Nanowerk News) Researchers at Japan Advanced Institute of Science and Technology (JAIST): graduate student Kulisara Budpud, Assoc. Prof. Kosuke Okeyoshi, Dr. Maiko Okajima and, Prof. Tatsuo Kaneko reveal a unique polysaccharide fiber in a twisted structure forming under drying process which showed spring-like behavior. |
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The spring-like behavior of twisted structures is practically used as a reinforced structure in a vapor-sensitive film with millisecond-scale response time. | |
This work is published in Small ("Vapor-Sensitive Materials from Polysaccharide Fibers with Self-Assembling Twisted Microstructures"). | |
Figure 1. Optical microscopy image of a single fiber of self-assembled polysaccharide in snaking, twisted, and straight structures. (Image: JAIST) | |
Polysaccharides play a variety of roles in nature, including molecular recognition and water retention. Still, there is a lack of study in vitro microscale structures of polysaccharides because of the difficulties in regulating self-assembled structures. | |
If the self-assembled structures of these natural polysaccharides can be reconstructed in vitro, it will lead not only to an increased understanding of the morphological changes involved in polysaccharide self-assembly in water but also to the development of a new class of bio-inspired materials, which exhibit regulated structures on a nanometer scale. | |
In this research, it is demonstrated that a cyanobacterial polysaccharide named sacran, can hierarchically self-assemble as twisted fibers from nanoscale to microscale with diameters of ∼1 µm and lengths >800 µm. this is remarkably larger than polysaccharides previously reported. | |
Unlike other rigid fibrillar polysaccharides such as cellulose, the sacran fiber is capable of flexibly transforming into two-dimensional snaking and three-dimensional twisted structures at an evaporative air-water interface (Fig.1). This twisted sacran fiber behaves like a mechanical spring under a humid environment. | |
To optimize the condition of the twisted structure is formed by controlling drying speeds. Actually, the drying speed and the capillary force are the dominant factors in creating these formations. | |
To show the potential use of this spring-like polysaccharide fibers, a crosslinked polysaccharide film is prepared as a vapor-sensitive material and the effects of the microfiber's spring behaviors in an environment with humidity gradient are demonstrated (Fig.2). | |
Figure 2. Schematic illustration of the humido-sensitive film composed of a snaking/twisted fiber network. (Image: JAIST) | |
The film reversibly and quickly switched between flat and bent states within 300-800 ms. This repulsive motion displayed by the film is caused by the snaking and twisted structures of the fibers responding to the change of moisture. The sacran film shows a fast response to the water drop retreating, changing from the bent state to the flat state. Because the extended sacran fibers have extension stress like a spring, the network could quickly release water by shrinking. | |
As a result, the bent film becomes flat immediately. Thus, the snaking and twisted fiber network enable millisecond bending and stretching responses to changes in local humidity. | |
From the simple method, JAIST researchers could create unique micro-spring from natural polysaccharide which is practically used as a vapor-sensitive material. Besides, by introducing functional molecules into the microfiber, it would be possible to prepare a variety of soft actuators responding to other changes in the external environment, such as light, pH, and temperature. | |
The method for preparing vapor sensors developed by this study not only improves understanding of how the motion of self-assembled structures responds to stimuli. But also contributes toward the design of environmentally adaptive materials with a high potential for sustainable use. |
Source: Japan Advanced Institute of Science and Technology | |
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