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首页> 外文期刊>The Journal of Chemical Physics >A nest of structures in dynamics of cellulose diacetate in N,N-dimethylacetamide in quiescent solution state studied by dynamic light scattering
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A nest of structures in dynamics of cellulose diacetate in N,N-dimethylacetamide in quiescent solution state studied by dynamic light scattering

机译：通过动态光散射研究静态溶液状态下N，N-二甲基乙酰胺中二乙酸纤维素的动力学结构嵌套

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In the quiescent state, dynamic light scattering measurements were performed for a polysaccharide, cellulose diacetate (CDA, the degree of substitution 2.40), in a liquid-crystalline promoting solvent N, N-dimethylacetamide (DMAc) in the range from dilute to crossover concentrations. Three modes of motions were detected simultaneously over all concentrations measured. They are in a nest of structures, which are caused by long-range interactions acting between OH groups of glucose units in a highly dielectric-constant solvent DMAc. Denoting these modes as Mode I, II, and III from fast to slow motions, the decay rates Gamma of each mode showed the squared scattering-vector dependence at lower angles, i.e., the diffusion nature. In dilute solution, fast Mode I is the translational diffusion of a single CDA chain and others represent the dissipation of locally associated CDA clouds which grow by the interactions specified above. Mode II is related to a coarse cloud formed in a limited time but spread over a wide space A, while Mode III is related to a dense cloud created with a very small space B inside A. The tentative increase in CDA concentrations in the spaces A and B relaxes to the level of bulk concentration with a large decay rate TLI for Mode II and a small TUI for Mode III. With the increase of c, the number of A and the bulk concentration increase, and the decay rate Gamma(III) for dissipating B becomes smaller than that in dilute solution. Above the crossover concentration c*, however, the space A becomes close each other and almost all the CDA are packed in A. Then fast Mode I represents the relaxation of concentration fluctuations, or cooperative diffusion, with the length scale as small as a single CDA chain, xi(I). Mode II represents another cooperative diffusion, which is originated by the relaxation of concentration fluctuations effective only in A of the correlation length xi(II) Mode III is related to the time-spade fluctuation in the distribution of A, which emerges as another cooperative diffusion of much larger correlation length xi(III). Mode II was contaminated by a self-diffusionlike (SF) motion, though both were separated into two branches in more concentrated regions. The SF mode is assigned to a reptation motion of CDA, which can be described by the constrained translational motion of a stiff chain in the tube with interacting wall. The dynamical feature of these modes of motions are influenced strongly by strength and nature of long-range interactions between unsubstituted OH groups in glucose residues, or the hydrogen bonds in solvents of high electronegativity. (C) 1998 American Institute of Physics. [S0021-9606(98)50448-5]. [References: 14]
机译：在静止状态下，在液晶促进溶剂N，N-二甲基乙酰胺（DMAc）中，对稀乙酸至交叉浓度的多糖双乙酸纤维素（CDA，取代度2.40）进行动态光散射测量。 。在所有测量浓度下，同时检测到三种运动模式。它们处于结构的巢中，这是由于在高介电常数溶剂DMAc中葡萄糖单元的OH基团之间的远程相互作用所引起的。将这些模式从快到慢分别表示为模式I，II和III，每种模式的衰减率Gamma在较低角度（即扩散性质）下显示出平方的散射矢量依赖性。在稀溶液中，快速模式I是单个CDA链的平移扩散，其他模式表示通过以上指定的相互作用而增长的局部关联CDA云的消散。模式II与在有限的时间内形成但分布在宽广的空间A上的粗糙云有关，而模式III与在A内的空间B非常小的情况下创建的密集云有关。空间A中CDA浓度的暂时增加B放宽到总体浓度水平，模式II的衰减率TLI大，模式III的TUI小。随着c的增加，A的数量和体积浓度增加，消散B的衰减率Gamma（III）变得比稀溶液小。但是，在交换浓度c *之上，空间A变得彼此靠近，几乎所有CDA都堆积在A中。然后，快速模式I表示浓度波动或协同扩散的缓和，其长度尺度小至单个CDA链xi（I）。模式II表示另一种合作扩散，其起因于仅在相关长度xi（II）的A中有效的浓度波动的缓和。模式III与A分布的时空波动有关，这是另一种合作扩散相关长度xi（III）更大。模式II受自扩散样（SF）运动的污染，尽管两者都在更集中的区域中分成了两个分支。 SF模式被分配给CDA的复制运动，这可以通过管中具有相互作用壁的刚性链的约束平移运动来描述。这些运动方式的动力学特征受葡萄糖残基中未取代的OH基团或高电负性溶剂中的氢键之间的长距离相互作用的强度和性质的强烈影响。 （C）1998美国物理研究所。 [S0021-9606（98）50448-5]。 [参考：14]

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