Measurement of apparent Brownian motion diffusion coefficient under finite spatial and temporal detector resolution

  • Adrielle Theresa DL. Cusi National Institute of Physics, University of the Philippines Diliman
  • Giovanni A. Tapang National Institute of Physics, University of the Philippines Diliman
  • Caesar A. Saloma National Institute of Physics, University of the Philippines Diliman

Abstract

We investigate the effect of binning size, N, and sampling interval, τ, on the accuracy of the measured diffusion coefficient via extensive Brownian motion analysis of solid probe particles (radius = 0.5μm) in a liquid of viscosity 0.95mPa-s at 300.65K. The theoretical diffusion coefficient is 0.46μm2/s as calculated using Stokes-Einstein relation while the apparent (observed) diffusion coefficient value which is based on the binned Brownian motion trajectories is determined using mean-squared-displacement analysis. We have observed a nonlinear increase in the apparent coefficient value with N and a decrease with longer τ values (lower frame sampling rates) with N ≥ 2 sizes leading to ≥ 1% deviations and N ≥ 3 sizes leading to ≥ 5% deviations at τ ≤ 0.5s. A maximum of 5% deviation was observed at around τ ≥ 4.0s, regardless of N. Our results indicate that detectors with greater spatial resolution are more desirable over detectors with faster sampling rates when measuring an accurate diffusion coefficient using Brownian motion analysis.

Published
2019-05-22
How to Cite
[1]
A. T. Cusi, G. Tapang, and C. Saloma. Measurement of apparent Brownian motion diffusion coefficient under finite spatial and temporal detector resolution, Proceedings of the Samahang Pisika ng Pilipinas 37, SPP-2019-1C-02 (2019). URL: https://paperview.spp-online.org/proceedings/article/view/SPP-2019-1C-02.
Section
Instrumentation, Imaging, and Signal Processing