Temperature effect on adsorption properties of silica-polyacrylic acid interface

The temperature influence on the adsorption mechanism of anionic polyacrylic acid (PAA) macromolecules on the silica surface was studied. For this purpose, the following techniques were applied: spectrophotometry, thermogravimetry, potentiometric titration and microelectrophoresis. This method allowed to determine the adsorbed amounts of polymer, changes in thermal characteristic of silica surface with adsorbed PAA, surface charge density of the solid as well as zeta potential of SiO(2) particles in the presence and absence of polyacrylic acid. All measurements were carried out in the temperature range 15-35 A degrees C. The free energies of adsorption were calculated from the adsorption data fitted by the Langmuir model. The obtained results of increase of PAA adsorption and its adsorption free energies with the rising temperature suggest that adsorbed polymer conformation changes from the coiled structure to more stretched one. Moreover, the polymer adsorption on the silica surface at 25 A degrees C leads to changes in the course of thermogravimetric curves as a result of surface properties modification of the solid by bonded macromolecules.