Department: Chemical and Biomolecular Engineering
Address: Mountaintop Campus
111 Research Drive
Bethlehem, PA 18015
Areas of Research
- Colloidal Systems
- Rheology of Dispersions
- Electrokinetic and Hydrodynamic Fractionation
Cesar Silebi focuses on research in three areas. First, he investigates interactions within colloidal systems. Most of his research involves the applications of transport phenomena principles to problems involving colloids and macromolecules. This activity includes theoretical and experimental investigations of the electrokinetic and hydrodynamic separation of colloidal dispersions using microcapillaries. Silebi collaborate with faculty from chemical engineering and other departments at Lehigh, studying both the thermodynamics and kinetics of the adsorption of polymers and their configuration on smooth planar surfaces as well as on the surface of colloidal particles. Other projects include rheological studies of aqueous colloidal dispersions and solutions of associative polymers, studies of the stability of colloidal dispersions, miniemulsion copolymerization, and interparticle transport in miniemulsions.
Second, he investigates the rheology of dispersions, using theory and experiments to elucidate the rheological behavior of solutions of water soluble associative polymers, colloidal dispersions, micellar dispersions and their mixtures. The work is primarily carried out using model systems of industrial interest. The model associative polymers used in these studies are block copolymers that are either hydroxyl (hydrophilic), or alkyl (hydrophobic) terminated backbones of poly (oxyethylene) of molecular weights ranging from 15,000 to 100,000. Efforts are aimed at developing structural models which are of great importance in interrelating the microstructure with their rheological behavior.
Lastly, Silebi's lab investigates electrokinetic and hydrodynamic fractionation of colloidal dispersions. Here, his interest is in developing models for the movement of charged colloidal particles, both spherical and non spherical, that include the forces of interaction between the particles and the surface of the capillary. In particular, the presence of electrostatic (due to the anionic surfactant present in the eluant) and steric (due to adsorbed non-ionic polymeric surfactants) repulsive forces are being systematically investigated. Current work involves studies of mixtures of anionic and non-ionic surfactants in order to provide a steric repulsive potential that will further decrease particle concentration near the surface of the capillary. The motion of the colloidal particles is achieved through either bulk fluid motion, electrokinetic forces, or external driving forces of gravitational or electrical origin. The theme of this research is a fundamental understanding of the role played by the physicochemical phenomena in the area of hydrodynamic and electrokinetic behavior of colloids and its application to fractionations. Of particular interest from a fundamental and practical viewpoint is the analysis of the colloidal particles after their separation in the flow field inside the capillary.