Author ORCID Identifier

Christopher L. Wirth

Document Type


Publication Date



This article describes the simulated Brownian motion of a sphere comprising hemispheres of unequal zeta potential (i.e., “Janus” particle) very near a wall. The simulation tool was developed and used to assist in the methodology development for applying Total Internal Reflection Microscopy (TIRM) to anisotropic particles. Simulations of the trajectory of a Janus sphere with cap density matching that of the base particle very near a boundary were used to construct 3D potential energy landscapes that were subsequently used to infer particle and solution properties, as would be done in a TIRM measurement. Results showed that the potential energy landscape of a Janus sphere has a transition region at the location of the boundary between the two Janus halves, which depended on the relative zeta potential magnitude. The potential energy landscape was fit to accurately obtain the zeta potential of each hemisphere, particle size, minimum potential energy position and electrolyte concentration, or Debye length. We also determined the appropriate orientation bin size and regimes over which the potential energy landscape should be fit to obtain system properties. Our simulations showed that an experiment may require more than 106 observations to obtain a suitable potential energy landscape as a consequence of the multivariable nature of observations for an anisotropic particle. These results illustrate important considerations for conducting TIRM for anisotropic particles.

Publication Title

The Journal of Chemical Physics





First Page



NSF No. 1344954


Cleveland State University Office of Research Startup Fund; National Science Foundation (NSF)


© 2017 Author(s). Published by AIP Publishing. This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Aidin Rashidi and Christopher L. Wirth , "Motion of a Janus particle very near a wall", J. Chem. Phys. 147, 224906 (2017) and may be found at



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