Dynamic Light Scattering Study of Structural Changes of Cellulose Diacetate in Solution under Couette Flow
| Autor: | Hiroyuki Kawanishi, Yoshisuke Tsunashima, Fumitaka Horii |
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| Rok vydání: | 2000 |
| Předmět: | |
| Zdroj: | Macromolecules. 33:2092-2097 |
| ISSN: | 1520-5835 0024-9297 |
| DOI: | 10.1021/ma9913055 |
| Popis: | Dynamic light scattering (DLS) measurements were conducted under a simple shear flow, i.e., the Couette flow field, to cellulose diacetate (CDA; a typical polysaccharide) in semidilute N,N-dimethylacetamide (DMAc) solution. The shear rate y was varied from 0 to 5.25 s -1 . At quiescence, CDA showed three dynamic modes, which correspond to two kinds of associations and a single chain. In the weakly sheared system (0.402 s -1 ≤ γ ≤ 5.25 s -1 ), the three dynamic modes collapsed, and alternatively two completely different modes were observed. The fast mode experienced a transition around y = 0.81 s -1 , the decay rate distribution changing from a broader bimodal to a narrower unimodal shape with increasing shear. The slow mode had a unimodal decay rate distribution, but the length scale of fluctuations was larger by 3 orders of magnitude compared to those observed at y = 0 s -1 ; that is, the length distribution was extremely uniform irrespective of y, and the length ξ s was proportional to γ -1 . This ξ s γ -1 relation was interpreted by Taylor's treatment of the behavior of viscous drops. Thus, the repetition of the burst and the coalescence growth of the associations was suggested for the slow mode. The ξ s γ -1 relation implied that CDA was molecularly disperse in DMAc under the viscometric field in a capillary viscometer at γ = 920 s -1 . |
| Databáze: | OpenAIRE |
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