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Low‐temperature dynamic light scattering. I. Structural reorganization and physical gel formation in cellulose triacetate/methyl acetate dilute solution at −99 – 45°C
Author(s) -
Tsunashima Yoshisuke,
Ikuno Masaya,
Onodera Gen,
Horii Fumitaka
Publication year - 2006
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.20479
Subject(s) - chemistry , cellulose triacetate , intermolecular force , metastability , solvent , solubility , molecule , hydrogen bond , dipole , crystallography , cellulose , organic chemistry
Curious low‐temperature solubility of cellulose triacetates (CTA; here we use nominally “CTA,” but the sample still contains 7% of C‐6 position hydroxyls) in an organic solvent, methyl acetate (MA), was studied by a newly designed low‐temperature type of DLS apparatus, which enabled for the first time to investigate the structural change of CTA in solution from 45°C down to −100°C. A molecularly dissolved CTA was found to coexist with three types of self‐assemblies over all the temperature ranges except for the three specific temperatures T * of 30, −10, and −75°C. However, these multiple self‐assemblies are not in real thermodynamic equilibrium but in a metastable state, which could be stabilized effectively by the intermolecular hydrogen bonding (HB) with the help of the dipole interaction at low temperatures. In more detail, with decreasing temperature, these assemblies performed the structural reorganization drastically at three T *'s and would finally be frozen in a physical gel structure at −99°C; around the freezing temperature of MA, CTA molecules could be trapped homogeneously in the frozen MA. The crucial role in such structural reorganizations is played by the balance between the intermolecular HB and the dipole interaction worked in the highly electronegative solvent. Because these interactions, which are mediated by the solvent electronegativity, change drastically with temperature, they result in the control of not only the single CTA chain conformation (= the intra molecular HB) but also the binding ways of the inter molecular HBs between CTA molecules and they induce multitudinous metastable structures in solution. Here it is noted that HB could work mainly between the C‐6 position hydroxyls in the anhydroglucose units of CTA and are essentially effective at low temperatures. © 2006 Wiley Periodicals, Inc. Biopolymers 82: 222–233, 2006 This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com