<p style="text-align: justify">Deposition of microbes and microparticles on silica (sand) surface is crucial in water filtration and biofilm formation. Adsorption and detachment of such colloidal particles are the results of the competition between attractive inter-surface forces and hydrodynamic shear in the presence of pipe flow. Net adhesion force depends on the geometry and mechanical properties of the particles, the chemistry of surfaces involved, and the ionic concentration of the electrolyte. Hydrodynamic shear depends predominantly on fluid viscosity, surface roughness, rotation of particles with different geometries, and velocity gradient of the boundary layer. Quartz crystal microbalance (QCM) induces a shear resonance on the sensor surface. The QCM device, oscillating in thickness shear mode of a quartz crystal substrate, is one of the most commonly used mass sensors for a wide range of chemical and biological applications. When particles naturally attach, the additional mass leads to hydrodynamic drag, raises the vibration inertia, and thus a shift in resonance frequency. QCM is a sensitive device to calibrate minute mass attached to the surface and is easy to be combined with real-time microscopy, enabling the use of QCM as a quantitative tool for colloidal particle deposition in water filtration.</p><p style="text-align: justify">In this study, a homemade single-channel microfluidic device integrated with a glass surface coated QCM sensor is designed and fabricated using glass and PDMS to characterize the adhesion of bacterial strains. To circumvent the complex biochemistry of live cells, colloidal polystyrene particles are used as model material. Filtration efficiency as a function of ionic concentration and flow speed is investigated systematically. Micron size polystyrene particles are suspended in potassium chloride (KCl) solutions of a range of ionic concentrations before being driven through the microfluidic channel at specific flow speeds. The number of attached particles is quantified by real-time QCM frequency measurement, and the deposition is monitored by optical microscopy simultaneously. Adhesion is found to be strong at high KCl concentration and low flow speed. The classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory is used to model the intrinsic surface forces of coupled van der Waals attraction and electrostatic double-layer repulsion and their impacts on the deposition process. &nbsp;The hydrodynamic shear acting on the particle surface in the hydrodynamic boundary layer provides the particle with the capability to escape from the collector surface. Data analysis shows consistency between the model and experimental measurements. The new microfluidic device is a powerful tool to quantify particle deposition and water filtration in the presence of an electrolyte.</p>

A Novel Microfluidic Device With a Built-in Quartz Crystal Microbalance (Qcm)  to Quantify Colloidal Particle Deposition in Filtration

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.