SGER: Hydrophobic Forces in Particle Adhesion

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AbstractCTS-04014019S. Beaudoin, Purdue UniversityThe role of hydrophobic forces in particle adhesion to surfaces in aqueous environments is not adequately understood. There is a need for the collection of data that will allow the hydrophobic effect to be quantified, and also for the development of theory to describe this effect. In this proposed work, atomic force microscopy will be used to measure directly the adhesion between particles and substrates of interest in aqueous solutions. The roughness of the substrate and the roughness and geometry of the particles will be measured before and after the adhesion forces are measured. The elastic properties of the particles and substrates will also be determined. With this information, particle adhesion models developed in the Beaudoin lab at Arizona State University will be used to quantify the van der Waals (vdW) and electrostatic (ES) interaction forces acting in these systems. These models take into account the effects of deformation and nonuniform geometry and morphology on the adhesion. After the vdW and ES forces are evaluated, the remaining forces in these systems will be attributed primarily to hydrophobic phenomena. In this fashion, a systematic experimental investigation of the hydrophobic interaction force for a number of particles of different size and geometry interacting with a number of surfaces will be performed. Contact angle measurements will be performed on flat sheets of material with the same composition as the particles and substrates used in the adhesion studies, so that the interfacial energies of the materials involved in the adhesion studies will be quantified. This data will provide the basis for a systematic evaluation of hydrophobic interactions between particles and surfaces. Once the form and magnitude of the effect of hydrophobic forces on the particle interactions has been established, it will be possible to develop appropriate theory to describe these effects. The intellectual merit in this proposed work lies in the measurement of the adhesion of deformable, rough, nonuniform particles to deformable, rough surfaces in aqueous solution using an atomic force microscope, and the use of recently developed, experimentally-validated models to describe vdW and ES forces in the adhesion of these particles. This will allow hydrophobic forces to be isolated for these systems. In this fashion, realistic particle-surface interaction forces can be measured with minimal confounding effects from the measurement technique, and the hydrophobic force isolated. The resulting data set will provide a comprehensive view of hydrophobic effects on particle adhesion that will serve as the basis for model development. The broader impacts of the proposed work lie in the importance of enhanced understanding of vdW, ES, and hydrophobic forces in a spectrum of high technology applications. Understanding and controlling the relative strengths of these forces will have a profound impact on the cleaning and sterilization of medical implants, the cleaning of wafers during semiconductor processing, the design of low-fouling coatings for high performance applications, and the development of new approaches for producing highly engineered surfaces with minimal contaminant levels during the fabrication of microelectromechanical systems (MEMS). The results will be disseminated at meetings of the Adhesion Society, the NSF/SRC Center for Environmentally-Benign Semiconductor Manufacture, the American Institute of Chemical Engineers, and the Electrochemical Society. The results will be published in the Journal of Adhesion.