| 研究実績の概要 |
Drying of aqueous solutions of megamolecular polysaccharide, sacran have been observed to deposit as self-assembled anisotropic structures comprising of high orientation. Upon drying the liquid crystalline (LC) solution from a limited space of 1 mm, a thin membrane was deposited vertically in the center of the container, bridging the two glass substrates. This phenomenon of space-partitioning was first of all studied theoretically using the equation of a meniscus. The drying interface in a limited space, splits from a single meniscus, into two menisci with the deposition of the membrane. An equation for this peculiar condition was derived and the total lengths of the meniscus over the drying interface were compared. From the calculations, it was also found that splitting of meniscus provided double the area for evaporation and the center position is most favorable. Thus, the formation of the vertical membrane was justified experimentally as well as mathematically.
Next, another high molecular weight polysaccharide, xanthan gum was evaluated for the space-partitioning property. The deposition of a horizontal lid-like membrane preceding the deposition of vertical membrane was seen. As xanthan aqueous LC solution changes to isotropic phase upon increase in temperature, the deposited xanthan membranous structures could be represented as a concentration-temperature-morphology phase diagram. Introduction of cross-linking points in the dried membrane with thermal annealing, anisotropically hydrogels with reversible swelling were designed.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
1: 当初の計画以上に進展している
理由
The initial research plan was to explain such a deposition behaviour of meniscus splitting by the polysaccharide solution in a limited space under a drying environment. By studying this phenomenon mathematically and modifying the standard equation of a meniscus according to these geometrical conditions, I was able to derive a general equation. This equation justifies the splitting of a single meniscus into two, and also represents the direct proportionality between the width of the container and the meniscus length. That is, it signals toward multiple splitting during evaporation upon increasing the width in a narrow gap.
Using xanthan gum as another polysaccharide, not just the phenomenon was generalized, but also the effect of temperature on the deposition was monitored. By regulating the temperature, it was possible to control the mobility of the LC domains and thus, define their orientation. Moreover, the effect of concentration and viscosity were also clarified. It was eventually possible to obtain a hydrogel, anisotropically swelling only along its thickness, reversibly.
The effect of surfactants in the prepared solution gave interesting results as the probability of the vertical membrane formation increased even with the use of lower concentration of polysaccharide solution. Additionally, the effect of change in humidity on the deposition behavior has also been completed and the manuscript is now submitted.
I received the Best Poster Presentation Award in the 1st International Conference on 4D Materials and Systems (Yonezawa, Japan) amongst approx. 100 candidates.
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| 今後の研究の推進方策 |
The research of space-partitioning involved rod-shaped LC domains of megamolecule polysaccharide, sacran in contrast to the generally studied spherical particles of other polymeric materials. In the next step, I plan to study the effect of platelet-shaped units co-existing with the rod-shaped in the LC polysaccharide solution. The preliminary results have demonstrated the ability of such a solution to bridge a gap of 5 mm and sometimes even 8 mm. Furthermore, the vertical membrane deposited, showed high orientation along one direction when observed under microscope with a retardation plate. The process of deposition and bridging of such a wide gap is now consideration. The aim is to validate the experiments with theoretical discussions on action of capillary forces in the drying process.
Also, the research till now has used aqueous solutions only. This time I hope to prepare samples in other solvents whichever imparts solubility and then check for any bridging depositions during drying. Maintaining the drying conditions with air circulation for different solvents will be a challenge as these polysaccharides are not easily soluble in organic solvents.
The extent of the role of gravity on the deposition process is also under consideration now.
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