A Study Of The Dynamics Of Self-electrophoretic Micromotors Near Chemically Modified Substrates

Self-propelled micromotor is a kind of colloid that can convert energy in the surrounding environment into mechanical work and perform directional motion.There is one kind micromotor called self-electrophoretic motor which is propelled by an electric field induced by chemical gradients.The mechanism of self-electrophoretic motor in the bulk solution has been studied for years and is relatively well understood.However,how these motors interact with boundaries is a newly developed research area that remains largely unexplored.On the one hand,there may be some important rules in such a system that can be used to steer motors.On the other hand,understanding how to use the interaction between motors and boundaries is crucial for future applications.In this essay,the dynamics of micromotors near boundaries of different parameters was discussed.First,by levitating motors with ultrasound,its motion in the bulk solution was compared with that near boundaries.We find that motors moved slightly more slowly near boundaries than in the bulk solution.Their directionality,however,was enhanced in the presence of substrates.Then,by hydrophobic treatment,we studied how motors responded to different surface wettability.We find that motors’ mobility was not sensitive to substrate wettability.Finally,through layer-by-layer assembly of polyelectrolyte on a substrate surface,we induced different surface charges and surface morphologies on substrates.Solution conductivity was changed because of ions leaching out of assembled polyelectrolyte.We find that both the surface roughness and solution conductivity have negative effects on motors’ mobility.In order to improve our understanding of the interaction between motors and walls,3-D simulation was performed with a numerical simulation package(COMSOL).Both the effects of the distance between motor and wall and the surface zeta potential of the substrate were studied.The simulation results show that motor’s speed increased when approaching the substrates.The compression of electric field was the main contribution.When substrate carried the same charges as motors,the induced electro-osmotic flow was in the opposite direction to motors’ movement.This effect became more remarkable as the charges increased.To summarize,this thesis has investigated the effects of different properties of boundaries on motors’ mobility and has advanced our understanding of the dynamics of motors in confined environment.In addition,it laid the foundation for future applications of self-propelled motors in confined spaces.