title: Direct force measurements between cellulose surfaces and colloidal silica particles.
abstract: 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.
authors.affiliation: Department of Inorganic, Analytical and Applied Chemistry, University of Geneva, Sciences II, 30, Quai Ernest-Ansermet, Geneva 1211, Switzerland.
authors.forename: Igor L
authors.initials: IL
authors.lastname: Radtchenko
authors.forename: Georg
authors.initials: G
authors.lastname: Papastavrou
authors.forename: Michal
authors.initials: M
authors.lastname: Borkovec
mesh_terms: D000327:Adsorption; D000465:Algorithms; D001672:Biocompatible Materials / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry; D002482:Cellulose / Q000737:chemistry*; D003102:Colloids / Q000737:chemistry*; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D007477:Ions; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D019563:Mechanics; D018625:Microscopy, Atomic Force; D015233:Models, Statistical; D008968:Molecular Conformation; D011312:Pressure; D011336:Probability; D011485:Protein Binding; D012822:Silicon Dioxide / Q000737:chemistry*; D055672:Static Electricity; D013499:Surface Properties
chemical_list: D001672:Biocompatible Materials; D002264:Carboxylic Acids; D003102:Colloids; D007477:Ions; D046911:Macromolecular Substances; D012822:Silicon Dioxide; D002482:Cellulose