Thermoresponsive Hydrogel of Diblock Methylcellulose: Formation of Ribbonlike Supramolecular Nanostructures by Self-Assembly

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• 作者：Atsushi Nakagawa ; Frank Steiniger ; Walter Richter ; Andreas Koschella ; Thomas Heinze ; Hiroshi Kamitakahara
• 刊名：Langmuir
• 出版年：2012
• 出版时间：August 28, 2012
• 年：2012
• 卷：28
• 期：34
• 页码：12609-12618
• 全文大小：756K
• 年卷期：v.28,no.34(August 28, 2012)
• ISSN：1520-5827

文摘

This article provides detailed insight into the thermoresponsive gelation mechanism of industrially produced methylcellulose (MC), highlighting the importance of diblock structure with a hydrophobic sequence of 2,3,6-tri-O-methyl-glucopyranosyl units for this physicochemical property. We show herein, for the first time, that well-defined diblock MC self-assembles thermoresponsively into ribbonlike nanostructures in water. A cryogenic transmission electron microscopy (cryo-TEM) technique was used to detect the ribbonlike nanostructures formed by the diblock copolymers consisting of hydrophilic glucosyl or cellobiosyl and hydrophobic 2,3,6-tri-O-methyl-cellulosyl blocks, methyl 尾-d-glucopyranosyl-(1鈫?)-2,3,6-tri-O-methyl-celluloside 1 (G-236MC, DP_n = 10.7, DS = 2.65), and methyl 尾-d-glucopyranosyl-(1鈫?)-尾-d-glucopyranosyl-(1鈫?)-2,3,6-tri-O-methyl-celluloside 2 (GG-236MC, DP_n = 28.2, DS = 2.75). Rheological measurements revealed that the gel strength of a dispersion of GG-236MC (2, 2.0 wt %) in water at 70 掳C was 3.0 times stronger than that of commercial MC SM-8000, although the molecular weight of GG-236MC (2) having M_w = 8 脳 10³ g/mol was 50 times smaller than that of SM-8000 having M_w = 4 脳 10⁵ g/mol. Cryo-TEM observation suggested that the hydrogel formation of the diblock copolymers could be attributed to the entanglement of ribbonlike nanostructures self-assembled by the diblock copolymers in water. The cryo-TEM micrograph of GG-236MC (2) at 5 掳C showed rectangularly shaped nanostructures having a thickness from 11 to 24 nm, although G-236MC (1) at 20 掳C showed no distinct self-assembled nanostructures. The ribbonlike nanostructures of GG-236MC (2) having a length ranging from 91 to 864 nm and a thickness from 8.5 to 27.1 nm were detected above 20 掳C. Small-angle X-ray scattering measurements suggested that the ribbonlike nanostructures of GG-236MC (2) consisted of a bilayer structure with a width of ca. 40 nm. It was likely that GG-236MC (2) molecules were oriented perpendicularly to the long axis of the ribbonlike nanostructure. In addition, wide-angle X-ray scattering measurements revealed that GG-236MC (2) in its hydrogel formed the same crystalline regions as 2,3,6-tri-O-methylcellulose. The influence of the DP of diblock MC with a DS of around 2.7 on the gelation behavior will be discussed.