Study On Fabrication Of Different Colloidal Particles And Self-propelled Behavior Of Active Janus Under Varied Boundary Conditions

Active matter can harvest energy from environment and convert it into kinetic motion or useful work.Due to its importance in the fundamental research as well as potential applications,it has become a hot research area in recent years.In this thesis,we first fabricated colloidal particles used for different active systems,and then we systematically studied the behavior of anactive Janus system driven by hydrogen peroxide under different boundary conditions.Firstly,in order to characterize the rotation of rod-shaped bacteria by marking the cell surface,we fabricated smooth hollow colloidal silica particles using Pseudomonas aeruginosa as template via the Stober reaction.One optimized reaction conditions are 2.5×10¹⁰/m L concentration of bacteria,1:1 methanol-water mixture 6m L,25%ammonia water 0.5 m L,TEOS 3 m L,and the reaction was stirred at room temperature for 2 h at a rate of 420 r/min.The fabricated silica shell particles and Pseudomonas aeruginosa were mixed,and the preliminary results showed some specific binding of silica shells and bacterial cells,which laid a foundation for further analysis of the rotation behavior of Pseudomonas aeruginosa.Then,polystyrene microspheres were synthesized by dispersion polymerization and were sulfonated.Hemispherical platinized Janus particles were then prepared using polystyrene spheres as substrate and the self-propelled behavior of Janus particles driven by hydrogen peroxide was studied.By observing the movement of Janus particles among different obstacles,the relationship between the motion behavior of self-propelled microspheres and environmental factors such as the shape andsize of obstacles,as well as the concentration of hydrogen peroxide was systematically studied.The results show that Janus particles can be trapped to circular posts of different diameters（3μm,10μm,20μm）or spheres（1.0μm,1.8μm,2.4μm,7.2μm）.With the increase of hydrogen peroxide concentration（1%-4%）or obstacle particle size,Janus microspheres are more likely to be trapped and the speed become faster.However,the movement speed of the Janus particles around the obstacle is always smaller than that in the smooth plane.Compared to the Janus particle around the sphere,Janus particles are more likely to be constrained by the circular posts.And we speculate that the capture behavior will only occur when the particle size of the obstacle is at least 1μm or greater.The self-propelled particle orientated against the obstacle with orientational angle stable to be larger than 90^°during orbiting,And when the position of the Janus particles around the obstacle is determined,the orientation angle is also fixed,and this orientation force is short-range.The results of this study contribute to the understanding of the behavior of self-propelled particles around the obstacles,and provide a basis for guiding the movement of active substances through intelligent control patterns in the future,such as guiding miniatures by engraving patterns or separating swimmer’s according to the speed.