MOBILIZATION OF A DEPOSITED PARTICLE BY A MOVING LIQUID-LIQUID INTERFACE AND ITS MOTION BEHAVIOR

This essay reports on the investigation of the mobilization of a particle initially deposited on a flat plate by a moving liquid-liquid interface. The topic is worth investigation for that the transport of colloidal particles in porous media and moving behaviors when driven by liquid-liquid interface can affect a broad range of industrial process, which are closely related to environment protection and nature resources recovery. Our experimental approach is motivated by results of recent molecular dynamics simulations showing different dynamic regimes during the detachment of a deposited nanoparticle by a moving interface. The main objective of this work is to perform experiments that mimic most of the conditions in the simulations and determine if similar dynamic regimes are observed. A second objective is to investigate the role of surface roughness on the remobilization of deposited particles by a moving fluid interface. To achieve our objectives, we characterized different particles’ motion as a function of the volumetric flow rate. The particles investigated are polymerized ethoxylated trimethylolpropane triacrylate (ETPTA) droplets of either 150μm or 400μm diameter. We control the roughness of the particles by coating different sized silica nanoparticles (150nm, 400nm, 520nm, 700nm) to the particle surface. For the mobilization experiments, particles are placed in glass tube, the oil phase is silicone oil and the aqueous phase is a mixture of water, dimethyl sulfoxide (DMSO) and sodium thiosulfate. By changing the moving speed of the oil-water interface inside the tube, different particles show different movement characteristics. We observe that particles tend to stay on the surface at low flow rates and start moving when the flow rate increases, followed by detachment at the highest flow rates. At intermediate flow rates, we observe a dynamic regime where the liquid-liquid interface first drags the particle along and then re-deposit the particle further down the microchannel. This regime was not observed in the molecular dynamics simulations. We attempt to obtain a qualitative understanding of the role of the flow rates on particle detachment by performing a force balance on the deposited particle. The force balance suggests that the most important factor on the particle remobilization is the contact angle dependence of the volumetric flow rate. To have better silica-coated ETPTA particles, the ETPTA’s surface property and wettability were studied and during which, an abnormal surface tension increase in water and color change were observed. A brief introduction and explanation of the phenomenon was also introduced in this work