Models of rebound and capture for oblique microparticle impacts

Simple algebraic, rigid body impact models using coefficients of restitution and coefficient of friction have been used extensively in the study of the impact of microparticles with surfaces. Recent work by the authors has shown that rigid body impact theory can be extended to include an adhesion coefficient to model oblique impacts of microparticles with surfaces in the presence of molecular level forces. In this paper, the model is fully described and exploited for engineering applications. The behavior of coefficients is investigated both analytically and experimentally as initial impact velocity and angel of incidence vary. As the initial velocity of microparticles grows smaller and smaller, the significance of adhesion forces increases, eventually reaching a point where no rebound occurs and the particle is captured. Equations for this region of the growth of the influence of adhesion, designed for empirically fitting, are presented. They are capable of representing the behavior of the material restitution coefficient and the adhesion coefficient for a wide variety of materials and conditions. Experimental results of several investigators are examined using these empirical equations. They not only do a remarkable job of representing adhesion in the transition from rebound to capture but are capable of explicitly determing the capture velocity. The paper also contains a study of the sensitivity of the impact coefficients to small changes in the angle of incidence. The dependence of the capture velocity on microsphere radius also is examined. (C) 1998 American Association for Aerosol Research.