Experimental Study On Brownian Motion Of Particles In Complex Fluid

The phenomenon of Brownian motion has been widely existed in nature and industrial areas, used in energy, biological, chemical, medical, environmental and other industries. With the development of micro-nano technology, the study on motion of micro/nano particle has become very important. In this study, the single particle tracking(SPT) technique was used to the visualized experimental study on the Brownian motion of sub-micro particles in complex fluid. The study includes three parts as follows:As preparation of the experiment, the SPT technique was used to measure the Brownian motion of sub-micro particles at five different diameters(0.2~2?m) in water at first. A continuous laser(532nm) and an electron multiplication CCD(EMCCD) camera as well as a microscope objective with amplification of 63? were used to obtain a series of particle images in the experiments. The images were processed by using Image J software, and Video Spot Tracker software was employed to get the single-step displacement of tracer particles in adjacent two images. The mean square displacements(MSDs) of particles within a period of time were calculated, and the experimental solutions of diffusion coefficients compared with the theoretical values based on the Stokes-Einstein equation were obtained accordingly. The results show that the probability density functions(PDFs) of single-step displacement of sub-micro particles obey the Gaussian distribution, and the experimental diffusion coefficients deviate from the theoretical diffusion coefficient less than 10%. The experimental results can reflect the Brownian motion characteristics of particles in simple fluid accurately.The experimental studies on Brownian motion of particles in complex fluid were carried out on the basis of accurate measurement of Brownian motion of particles in the water. Detergent solution and glycerin which are two kinds of organic solvents were chosen to mixed with water for the preparation of complex fluid media, whose concentration ratios were from 5: 100 to 20: 100 for the former and from 5: 100 to 100: 100 for the latter, respectively. The SPT technique was employed to get the single-step displacement of fluorescent sub-micro particles at two different diameters 0.2μm and 0.52μm, respectively. The statistical analysis results show that the PDFs of single-step displacements of sub-micro particles in two kinds of complex fluid media still obey the Gaussian distributions which are consistent with the experimental results in the water. What differences from the situations in water experiments are that the MSDs of the particles in two fluid media show power law, i.e.2r(t) t?? ? ? and so the diffusion coefficients have the forms of power function as 1t?-?, which belong to the typical fractional diffusion. Because all the power coefficients, ?, satisfy the range of 1 ?? ?2, the fractional diffusions have the characteristics of super-diffusion. The statistical averages of the diffusion coefficients of two kinds of solution under different concentrations were calculated in order to observe the distributions of the diffusion coefficients with the variations of concentration. It can be seen that the diffusion coefficient of each particle has the decreasing trend with increase of the solution concentration, which indicates that the organic solutions have the restriction roles on particles diffusion.In order to obtain the statistic characteristics of Brownian motions of particles, all the ergodicity breaking(EB) of particle trajectories in water, detergent and glycerol solution were analyzed. The results show that the EB parameters of all random diffusion processes in three kinds of fluids are in the same order of magnitude( 0.1 ?E ?0.8). The experimental results indicate that the statistical characteristics of random diffusion processes of the two organic solutions which have the super-diffusion characteristics are consistent with that of the normal diffusion.