Deposition Of Colloidal Particles From Electrokinetic Flow Suspension In A Microfluidic Channel

Microfluidic devices consist of microchannels and microstructures with possible integration of signal conditioning and processing circuitry that can be fabricated using microfabrication technologies. The past decade has seen academic frenzy for microfluidics research that involves multidisciplinary fields including engineering, physics, chemistry, biology, and medicine. The fast development of microfluidics mainly lies in its two important applications (i) as a new generation of instrumentation for performing chemical and biological assays, and (ii) as a platform for studying fundamental physical and biochemical processes; both applications usually involve samples that carry bio-particles such as macromolecules (e.g., protein, DNA), bacteria, cells etc. Researchers have shown that biofouling often occurs on microfluidic channel surfaces. The presence of biofouling may cause several unwanted consequences such as hindrance to the optical detection, loss of samples, change of channel surface properties, reduction of accuracy and resolution etc. From a fundamental viewpoint, the phenomenon of biofouling in a flow medium exhibits the coupling among hydrodynamics, colloidal science and surface chemistry. For simplification, a model system involving Brownian particles deposition from flowing suspension in a microchannel can be a good representative to simulate complex microfluidic fouling processes. The advantages of such a model system are multi-folds: (i) the hydrodynamic flow is well-characterized and well-controlled so that the role played by hydrodynamics in particle deposition can be explored; (ii) in the literature colloidal particles are widely used to mimic bio-particles to reveal the dynamic nature of the short-range surface forces not only between particle and the fouling surface, but also between flowing and deposited particles; and (iii) importantly the use of video-microscopic technique allows for directly visualizing particle behavior during the deposition process. Therefore, an in-depth study of particle transport and deposition in microchannels not only could provide insight into the underlying mechanisms of biofouling but also offer guidance for the optimal design and better control of microfluidic devices.In this book chapter, the physical integration of the mechanisms contributing to particle deposition is furnished. Experimental studies of particle deposition are reported under various hydrodynamic and physiochemical conditions. A mathematical model based on the Brownian Dynamic Simulation technique is presented to compute the particle trajectories and consequently, the deposition rate. The simulation results are verified through experiments. Particularly, the deposition of particles from electrokinetic flows is considered because electrokinetic flow has been widely used in microfluidic devices to offer an efficient and effective transport mode in microchannels because it posses numerous advantages over conventional pressure-driven flow including simple design, ease of fabrication and integration, no moving parts, and fine control.