Effects of pollen and metal oxide pollen replica morphology on tailorable dry and wet adhesion

Abstract

The surface adhesion of micro-particles has been investigated with respect to many natural and environmental phenomena as well as engineering applications including drug delivery, coating, paints, separations, and sensors. Especially, the surface adhesion of smooth micro-particles with simple shapes (spheres, cylinders, hexahedrons) has been well-studied for the last four or five decades. However, there are far fewer studies of the adhesion of micro-particles with complex surface morphology. In this study, pollen grains are used as experimental samples and bio-templates since the pollen grains have chemically and physically stable surface with wide shape diversity. The purpose of this study is to understand the dry and wet adhesive mechanisms of pollen and pollen replica adhesion to tailor the magnitude and rate-dependence of the adhesion. During the investigation of the mechanisms, we have learned: i) how to analyze quantitatively and model the attraction force of micro-particles with complex surface micro- and nano-scale morphology ii) the effects of both particle morphology and liquid physical properties on wet adhesion of micro-particles on surfaces iii) how to tune the rate-dependence of the wet adhesion via control of surface morphology and the structure of liquid phases. Not only do these discoveries offer insight into the mechanisms operative in Nature, but they also offer inspiration for new adhesion mechanisms for micro-particles, particularly those that are responsive to the dynamics of particle detachment speed.