Weakly Charged Polyelectrolyte Adsorption to Glass and Cellulose Studied by Surface Force Technique

Abstract

Interaction forces were measured between glass surfaces and between one glass and one cellulose surface in the presence of a 10% charged, random copolymer of acrylamide and cationic [3-(2-methylpropionamido)-propyl]trimethylammonium chloride (AM-MAPTAC-10), using a noninterferometric surface force technique (MASIF). Adsorption to glass from a 1 ppm solution leads to neutralization of the substrate negative surface charge. When the bulk polymer concentration is increased to 50 ppm, a weak charge reversal occurs as indicated by the reappearance of the double-layer force. Throughout the concentration range studied (1-50 ppm), the forces measured on approach between two glass surfaces could be adequately described by the DLVO theory. The interactions between one glass and one model cellulose surface under the same conditions follow a different pattern. AM-MAPTAC-10 adopts an extended conformation upon adsorption to cellulose and steric repulsion is generated when the thick adsorbed layer is compressed. The different structure of the adsorbed layers on cellulose is explained in terms of its lower surface charge density compared to glass. This leads to fewer attachment spots on the solid surface and an increased amount of polymer loops and tails proturding into solution; i.e., thicker adsorbed layers are formed and the resulting system is sterically stabilized.