Microfiber suspensions for the removal of adhered colloids from surfaces, microdevices, and cavities

Abstract

Effective methods for cleaning surfaces are important for applications including dentistry, healthcare, micro-devices, and the manufacturing of electronic components and semiconductors. For example, surgical and dental instruments are susceptible to accumulation of aggregates and biofilm formation, which can lead to cross-contamination when ineffectively cleaned and reused. Complex fluids such as micro-fibrillated cellulose (MFC) can greatly assist in mechanically cleaning surfaces by removing strongly adhered aggregates without abrading the underlying material. We demonstrate that the heterogeneous structure of micro-fibrillated cellulose is effective in removing adhered particulates from surfaces and we characterize the cleaning efficiency of MFC suspensions in representative flow configurations. The experiments reported here involve flowing MFC solutions at various concentrations and at controlled shear rates through a rectangular microfluidic channel. Fluorescence microscopy is used to measure the removal of fluorescent particles that are adhered to the glass surface of the microfluidic device by electrostatic and surface forces. The particle removal with time is analyzed for each concentration of the MFC suspension and each shear rate to determine cleaning effectiveness. The rheology of the MFC solutions is also characterized and correlated to cleaning performance. We find that cleaning effectiveness increases with increasing fiber concentration and with increasing shear rate. Additionally, we compared the cleaning performance of the MFC suspensions with fluids that share similar rheological properties to highlight the role of shear thinning, elasticity, and tribology. Finally, we examine how sharp corners/edges within a microfluidic channel hinder cleaning and identify strategies for mitigating this hindrance.