| AVS 58th Annual International Symposium and Exhibition | |
| Surface Science Division | Tuesday Sessions |
| Session SS-TuP |
| Session: | Surface Science Poster Session |
| Presenter: | Berkem Ozkaya, University of Paderborn, Germany |
| Authors: | B. Ozkaya, University of Paderborn, Germany G. Grundmeier, University of Paderborn, Germany |
| Correspondent: | Click to Email |
Sequential adsorption of oppositely charged polyelectrolytes leads to multilayered thin films via electrostatic self-assembly. Incorporation of sheet-like inorganic nanoparticles is a promising method to improve barrier and ion transport properties, as well as mechanical properties in such films. The interface chemistry between the nanosheets and the polyelectrolyte segments plays a crucial role on design of thin coatings with tailored properties. In the present study, we have investigated the effects of pH and ionic strength on the adsorption of single polyelectrolyte molecules on natural clay (Na-Montmorillonite) platelets by means of AFM-based single molecule force spectroscopy (SMFS). SMFS is one of the few methods where in-situ experiments can be performed to obtain precise and quantitative information on interaction forces at a molecular level. In order to perform SMFS on clay platelets (lateral size: 50-300 nm), a heterogeneous model surface has been obtained via electrostatic immobilization of exfoliated clay platelets on template stripped ultra-flat Au(111) surfaces. Probe molecules (polyallylamine) were covalently attached to the gold coated AFM cantilever. Equilibrium desorption plateaus of constant force were obtained from the successive force-distance measurements. By adjusting the ion valency in the electrolyte, selective information from clay platelets could be obtained. In the presence of monovalent ions, desorption plateaus of constant force in the range of ~50 pN were obtained from pH 3 to pH 7. At pH values above the pKb value of polyallylamine,-confirmed with polarization modulation infrared reflection absorption spectroscopy (PM-IRRAS) measurements on cast polyallylamine- no detectable desorption event took place. The constant negative surface charge of clay platelets simplifies the evaluation of effects of electrical double layer and polymer line-charge density on adsorption of the polyelectrolyte molecules. Overall, the results of pH and ionic strength dependent de-adhesion measurements provide valuable information on the interplay between surface properties and polyelectrolyte adsorption giving the basis for an improved understanding of the behavior of silicate nanoparticles in polyelectrolyte films.