Particle adhesion and removal in ethanol/water mixtures

Adhesion and removal of particles to and from substrates were investigated in water, ethanol and ethanol/water mixtures. Spherical polyethylene and nylon particles of 4-5 ,um in diameter were used. Plates of polyethylene, polyvinylidene chloride, polyvinylidene fluoride, polyethylene terephthalate, and nylon 6 were used as substrates. A plate was perpendicularly immersed in the suspension, and the number of particles adhering to the plate was counted using a microscope video system. Since polyvinylidene chloride (PVDC) substrate showed the maximum particle adhesion in water for both kinds of particles, the particle removal experiments were carried out using the PVDC plates. The PVDC plate to which particles in water adhered was immersed in an ethanol/water mixture. The number of particles remaining on the plate was counted, and this determined the particle removal efficiency. The number of adhering particles decreased with increasing volume ratio of ethanol in the ethanol/water mixtures, and only a few particles adhered to all the substrates in the ethanol volume ratio above 30%. The particle removal efficiency increased with increasing volume ratio of ethanol and reached 90% in the ethanol volume ratio above 30%. The experimental results obtained are discussed in terms of electrokinetic potentials, Hamaker constants, and surface free energies. The particle adhesion and removal phenomena were essentially explained in terms of the free energy changes which were estimated from the dispersive and nondispersive surface free energies of the particle, substrate and liquid.