Direct Force Measurements between Cellulose Surfaces and Colloidal Silica Particles

• Published in: Biomacromolecules 2005-11, Vol.6 (6), p.3057-3066
• Main Authors: Radtchenko, Igor L, Papastavrou, Georg, Borkovec, Michal
• Format: Article
• Language: English
• Subjects: Adsorption; Algorithms; Applied sciences; Biocompatible Materials - chemistry; Carboxylic Acids - chemistry; Cellulose - chemistry; Cellulose and derivatives; Colloids - chemistry; Exact sciences and technology; Hydrogen Bonding; Hydrogen-Ion Concentration; Ions; Macromolecular Substances - chemistry; Materials Testing; Mechanics; Microscopy, Atomic Force; Models, Statistical; Molecular Conformation; Natural polymers; Physicochemistry of polymers; Pressure; Probability; Protein Binding; Silicon Dioxide - chemistry; Static Electricity; Surface Properties
• ISSN: 1525-7797; 1526-4602
• DOI: 10.1021/bm050371d

The interaction of cellulose layers with colloidal silica particles was investigated by direct force measurements with the atomic force microscope (AFM). Upon approach, repulsive forces were found between the negatively charged silica particles and the cellulose surface. The forces were interpreted quantitatively in terms of electrostatic interactions due to overlap of diffuse layers originating from negatively charged carboxylic groups on the cellulose surface. The diffuse layer charge density of cellulose was estimated to be 0.80 mC/m2 at pH 9.5 and 0.21 mC/m2 at pH 4. The forces upon retraction are characterized by molecular adhesion events, whereby individual cellulose chains desorb from the probe surface. The retraction profiles are dominated by well-defined force plateaus, which correspond to single-chain desorption forces of 35−42 pN. We surmise that adsorption of cellulose to probe surfaces is dominated by nonelectrostatic forces, probably originating from hydrogen bonding. Electrostatic contributions to desorption force could be detected only at high pH, where the silica surface is highly charged.