Using the Multiasperity Models to Investigate the Effect of Cylindrical Micro/Nanoparticle Roughness on the Critical Manipulation Forces

In this paper, the process of moving rough cylindrical bacteria micro/nanoparticles on a smooth substrate by means of an atomic force microscope's (AFM) probe has been investigated. For this purpose, three common adhesion models of Rumpf, Rabinovich, and Cooper have been further developed in the form of multiasperity contact models and with regards to the cylindrical geometry of bacteria nanoparticles. The number of asperities in contact and also the areas of contact between nanoparticle/substrate and nanoparticle/AFM probe tip have been calculated. Then, a dynamic model for simulating rough cylindrical nanoparticles displacement on a smooth substrate has been presented and adhesive forces obtained from the aforementioned three models have been employed in this model to determine the critical force and time values for onset of rolling and sliding of particles on the substrate. Then, the effect of geometrical and roughness parameters on critical forces has been investigated. The simulation results have shown that critical forces required for pushing a rough particle are less than a smooth one. Also, the simulation results indicated that with increasing particle radius, the critical sliding force increases while the critical rolling force diminishes. For the results to be more realistic, simulations have been performed based on the roughness and geometrical parameters extracted from topographical images of bacteria micro/nanoparticles. For this purpose, two different bacteria samples were obtained and after preparing them, the topographic images of these samples were acquired by means of the AFM. Then, the roughness and geometrical parameters of these particles were extracted from the topographic images and using these parameters the manipulation process was simulated for these particles. The simulation results indicate that the maximum difference between Rumpf and Rabinovich models is 8%, so these model results are in a good agreement. Finally, the models developed in this research were validated by comparing the results with the findings of a research on gold nanoparticles.