The filtration effect of irregular-shaped, real-world particles, such as silicon, alumina, and silicon nitride particles, has been experimentally investigated using 0.1, 0.22, and 0.45-μm-rated polyvinylidence difluoride (PVDF) and 0.2-μm polytetrafluoroethylene (PTFE) membrane filters. Particle retention tests were performed by measuring particle concentrations upstream and downstream of the test filter using an automatic liquid-borne laser particle counter (LPC). The test apparatus for the particle retention studies used a pump-driven water recirculating system.
Zeta potential values play an important role in liquid filtration. The higher-charged particles, such as PSL and silicon, degraded filter efficiency during filter loading, while the lower-charged alumina and silicon nitride particles achieved complete retention over the entire range of test particle size, i.e., from 0.1 μm to 0.4 μm. Experimental results showed that if the filter and contaminant particles had a high charge of similar polarity, the electric double layers would interact in a repulsive manner, making the adsorptive deposition of the particle unfavorable and leaving sieving as the active filtration mechanism. If the contaminants had a low charge, they coagulated due to colloidal instability and were easily retained on the pore surfaces.