Study On Enhanced Brownian Motion Of Group Janus Particles Based On Dynamic Light Scattering

Janus particles are non-uniform particles that own different properties at two different sides of the particle.Due to the nature of its asymmetry,the functionalized Janus particles can make use of"fuel"in the environment to perform asymmetric physical or chemical reactions,thereby forming the gradient fields of different physical quantities,such as concentration,electric field or light intensity around the particles.The asymmetrical momentum distribution formed by the gradient performs autonomous motion,which is the so called self-propelled Janus particles.Due to the highly sensitive dependence of Janus particles'self-propelled characteristics on the reaction conditions?such as reactant concentration?and their external driving force of self-propulsion,they have a wide range of applications in water environment monitoring and repairing,life medicine,and other fields.Therefore,how to accurately and efficiently characterize the self-propelled behavior of single/collective Janus particles,such as diffusion coefficient,self-propelled speed,motion trajectory,etc.,becomes the basis for their application.The self-propulsion of Janus particles is not isolated,but interactive.From the macroscopic point of view,the self-propulsion of group Janus particles is different from the self-propulsion of individual Janus particles.Most scholars only study the self-propulsion of individual Janus particles.In this paper,the self-propelled motion of the group Janus particles is studied experimentally using Dynamic Light Scattering?DLS?.The experimental object is 1?m Pt-SiO₂ Janus particles?fabricated with electron beam evaporation and spin coating technique?.Since the micro-nano-particles are prone to aggregation,the de-aggregation of Janus particle based on DLS is studied in this paper firstly.In the experiment,the de-aggregation of Janus particles at different ultrasonic times is explored.Experimental results show that ultrasound can de-agglomerate Janus particles,and the ultrasonic de-aggregation lasting for 3 minutes is better than the ultrasonic de-aggregation lasting for 5 minutes.Then,the experimental study of de-aggregation of anti-flocculation agent NaOH and cationic surfactant?Hexadecyl trimethyl ammonium Bromide?CTAB??for 3 minutes is performed in this paper.Experimental results show that after the CTAB treatment,the Janus particles reach a monodisperse state,but the CTAB adsorbs on the solid-liquid interface of the Janus particles to form a CTAB molecular film on the surface of the Janus particles,which may affect the catalytic effect of Pt,thus making the Janus particle's self-propelled velocity decrease.Finally,the self-propelled motion of Pt-SiO₂ Janus particles with nominal diameter of 1?m in pure water and different concentrations of H₂O₂ solution is studied by DLS.The experimental results are compared with the results obtained by the SPT in the previous group research.The experimental results show that the self-propelled motion of Janus particles is manifested as enhanced Brownian motion.With the increase of the concentration of H₂O₂ solution,the effective diffusion coefficient of the population of Janus particles measured by DLS increases is larger than the diffusion coefficient of Brownian motion in pure water,but less than the effective diffusion coefficient of single Janus particle measured by SPT.In addition,in the DLS measures,a decrease in the relaxation time of the group Janus particles is found.In this paper,the mean square displacement of group Janus particles in a very short time interval is derived by inversion calculation using the autocorrelation function measured by DLS.The results show that at the same observation time interval,the mean square displacement increases with the increase of the concentration of H₂O₂ solution;in the same concentration of H₂O₂ solution,the mean square displacement increases with the increase of observation time interval.Finally,this paper compares and analyzes the difference between DLS and SPT in the study of Janus particle motion behavior,and points out that the observation time interval is an important factor influencing the experimental results of DLS and SPT.