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A particle roughness analysis tool, based on electron microscopy (EM) images. The influence of various parameters on the calculated roughness was also investigated: the setting of the proper threshold, accelerating voltage, etc. The samples were gradually tilted to extend imaging information of more than only one projection. Furthermore, the measurement uncertainty of the profile roughness of particles associated to various orientations was estimated.
This study describes the motion of magnetizable particles of spherical shape with radius at most of 1 μm, also referred to as microbeads, immersed in a liquid under laminar flow conditions in a microfluidic channel. An external magnetic field is applied in part of the system such that it permeates the channel and is characterized by a spatially varying magnetic field, i.e., the gradient of the magnetic field is nonzero. The beads are superparamagnetic; hence they can reach high level of magnetization in the presence of a magnetic field, and this magnetization disappears when the field is zero. Therein lies the attractiveness of these microbeads and the potential for applications because their motion can be controlled using an external magnetic field. The motion is governed by several factors, including the magnetic force acting on microbeads (particles), the drag force due to viscosity, the interaction between particles and the fluid, as well as the interaction between particles themselves. For a single particle case, the trajectory of the motion is determined by balancing the drag and magnetic forces acting on the particle, a calculation that in general requires numerical integration. For a system consisting of an ensemble of interacting particles, several regimes of motion dominated by one of the factors are identified. Of particular interest are the systems dominated by the large number of particles in the ensemble, i.e., high particle concentration, in which cases the wake influences the flow downstream. This effect is qualitatively investigated by considering the Navier-Stokes equation with and without the magnetic force contribution.