(362a) Quantitative Analysis of Iron Oxide Pollen Replica Short- and Long-Range Interactions

The purpose of this study is to learn how to: i) tailor the attraction forces of three-dimensional biogenic microparticles though synthetic chemical processing and ii) apply theoretical modeling to analyze such attraction forces. Native pollen particles have been converted into 3-D magnetic oxide replicas via use of a highly-conformal, surface sol-gel (SSG) coating process. The average nanoscale crystal size of the pollen replicas was controlled via thermal treatment. The prepared replicas were attached to AFM cantilevers, and short- and long-range attraction forces between the replicas and substrates (Ni, Cu, Au, and Ni-Nd) were evaluated with the scanning probe microscope. A multi-sphere Hamaker model and a sphere-plane magnetic force model were used to model the short- and long-range interactions, respectively. A reproducible non-monotonic relationship was observed between the average crystal size of the oxide replicas and the short-range vdW interaction. This correlation was attributed to the competing effects of crystal size on vdW interaction and on the number of crystals in the vdW interaction range, and this tendency was explained by the multi-sphere Hamaker model. The long-range force was also tailored by adjusting the average crystal size, because an increase in grain size resulted in an increase in the magnetization of the replicas. The measured long-range force behavior agreed well with the sphere-plane magnetic force model. By combining native pollen structures with magnetic oxide chemistry, and controlling the average crystallite size of the ceramic pollen replicas, both short-and long range attraction forces could be tuned in a novel manner.  These bioinspired replicas have potential for a wide range of applications in sensors, catalysis, and separations processes.