Calibration and error analysis of a new magnetic sphere microrheometer

Abstract

A magnetic microrheometer has been built, which can be used to study the rheological properties of materials that are available in small volumes and have distinct phases. The instrument performs creep tests (displacement in response to an imposed force), using magnetic microspheres of diameter 7 μm and larger. Displacement histories of the spheres are video-recorded and analyzed, with high resolution, using computer vision methods. In this article, results are presented for the magnetic force calibration and for a test using a Newtonian fluid to evaluate the performance of the instrument. A comprehensive analysis of the different sources of error in measuring Newtonian fluid viscosities was performed, resulting in quantitative delineation of the accuracy and precision of the microrheometer.