Charging and swelling of cellulose films
Charging and swelling of cellulose films
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DOI：
10.1016/j.jcis.2007.02.047
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发表时间：
2007-05-15
影响因子：
9.9
通讯作者：
Werner, Carsten
中科院分区：
文献类型：
--
作者：
Freudenberg, Uwe;Zimmermann, Ralf;Werner, Carsten
纤维素在水环境中的充注和膨胀是对纤维素基产品性能和应用最感兴趣的问题。为了揭示生物聚合物水凝胶的离子化和结构特征之间的相互作用，我们比较了非交联和交联的纤维素薄膜，基于唐南电位的测定杜欣，R. Zimmermann， C. Werner， J.胶体界面科学，274(2004)3091，来自微缝电动力学（流电位/流电流）实验和来自椭圆偏振的层厚度。反映纤维素膜内羧酸基团电离的Donnan电位的pH依赖性与反映纤维素膜最上层表面特征的流动电流的相关趋势显著不同：当膜表面的羧酸基团作为孤立的官能团离解时，纤维素层内电离基团的静电相互作用导致羧酸的不完全离解（pK位移）和在碱性pH范围内的层膨胀（膨胀）。研究发现，即使在层的结构限制（交联）和溶液离子强度较低的情况下，通过进一步降低羧酸功能的解离程度，该体系也会限制其体积电荷密度。这些发现归因于纤维素的无定形区优先氧化引起的羧酸基团的局部积累和层内有序的水结构。(C) 2007爱思唯尔公司版权所有。
Charging and swelling of cellulose in aqueous environments are of highest interest with respect to the performance of cellulose based products and applications. To unravel the interplay between ionization and structural features of the biopolymer hydrogel we compared non-cross] inked and crosslinked cellulose thin films based on a determination of the Donnan potential [S.S. Dukhin, R. Zimmermann, C. Werner, J. Colloid Interface Sci. 274 (2004) 3091 from microslit electrokinetic (streaming potential/streaming current) experiments and layer thicknesses from ellipsometry in aqueous electrolyte solutions. The pH dependence of the Donnan potential, reflecting the ionization of carboxylic acid groups within the cellulose films, was found to be significantly different from the related trend of the streaming current which reflects the characteristics of the topmost surface of the layers: While carboxylic acid groups on the surface of the films dissociate as isolated functionalities, the electrostatic interactions of ionized groups within the cellulose layers cause an incomplete dissociation (pK shift) of the carboxylic acid and a layer expansion (swelling) in the alkaline pH range. The system was found to restrict its volume charge density even after structural restrictions (crosslinking) of the layer and at lower ionic strength of the solutions through a further decrease of the degree of dissociation of the carboxylic acid functions. These findings were attributed to the local accumulation of the carboxylic acid groups caused by preferential oxidation of the amorphous regions of the cellulose and to the ordered water structure within the layer. (C) 2007 Elsevier Inc. All rights reserved.