Simulation And Experimental Studies Of Self-propelled Micromotors Based On Gradients

Self-powered micromotors are a kind of intelligent biomimetic materials which can convert energy in the surrounding environment into autonomous motion. Based on the above features, micromotors can be applied in biomedicine, environmental monitoring, bicochemical analysing and other fields. The working mechanisms of micromotros based on gradients are relatively well-understood among various micro/nano- motors. In addition, these micromotors can dynamically self-assemble at microscale in a way slimilar to natural microorganisms such as bacteria. Compared to microorganisms, advantages such as uniformity and controllability in size/shape make the gradients-propelled micromotors a good model system for studying self-assembly. Furthermore, the study of interaction between micromotors and dynamic/static structures is significant for understanding collective behaviors in nature as well as for the synthesis of low-dimensional materials.Many types of gradients-propelled micromotors have emerged in the last decade. Among them, bimetallic rod micromotors have been studied for the longest time, while their propulsion mechanism is complicated involving the coupling of multiple physics fields. In this thesis, 2D axisymmetric and 3D numerical models of bimetallic rod motor based on self-electrophoresis were built with COMSOL software package to study the motor-structure and motor-motor interactions. Based on these models, the relationship between motor velocity and the motor geometry parameters was studied. In addition, the acceleration of motors in microchannels was studied, and various parameters such as channel diameters, motor lengths and motor surface reaction rates were investigated. Simulation results indicate that the squeezing of electric field around the motor plays an important role in the motor acceleration. Besides, the relationship between interaction forces and relative distances of two motors as well as motor-passive particle were studied. By comparing the simulation results with experimental results, we provide the preliminary confirmation on the validity of the model.The popular study of collective behaviors at microscale also calls for novel synthetic micromotors of rich kinetics. Inspired by the self-electrophoretic COMSOL model, a similar model of Janus motor based on self-diffusiophoresis was built, and PMMA-Ag and PMMA-AgCl Janus motors were fabricated based on the model. In our experiments, we observed periodic pulsing motion of PMMA-Ag motors in H2 O2 and KCl solution under UV light, and the effect of various parameters on the periodicity of motion was also studied. A preliminary mechanism involving oscillating chemical reactions which lead to self-diffusiophoresis of Janus motors was proposed based on simulation results. In addition, motion of PMMA-Ag Cl Janus motor was achieved in DI water irradiated by UV light, and the velocity and mean square displacement of these motors were also measured in different concentrations of KNO3.The results from this thesis improved the understanding of the propulsion mechanism and interactions of self-electrophoretic micromotors, and also produced more varieties of gradients-propelled micromotors that are useful as model systems to study active matter.