Charging and swelling of cellulose films

• Published in: Journal of colloid and interface science 2007-05, Vol.309 (2), p.360-365
• Main Authors: Freudenberg, Uwe, Zimmermann, Ralf, Schmidt, Kati, Behrens, Sven Holger, Werner, Carsten
• Format: Article
• Language: English
• Subjects: Carboxylic Acids - chemistry; Cellulose; Cellulose - chemistry; Chemistry; Donnan potential; Electrochemistry; Exact sciences and technology; General and physical chemistry; Hydrogen-Ion Concentration; Kinetics; Membranes, Artificial; Models, Chemical; Porosity; Solutions - chemistry; Surface conductivity; Surface Properties; Swelling; Water - chemistry
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2007.02.047

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-crosslinked 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) 309] 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 (p K 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. Charging and swelling of cellulose films were studied in aqueous electrolyte solutions. For that aim the surface conductivity, Donnan potential and layer thickness were investigated by microslit electrokinetic experiments and ellipsometry.