Scattering Enhancement Effect Of Surface Charges On Mesoscopic Spherical Particles

In the theory of particle surface electrokinetics,the surface of any particle always carries more or less charges.When the surface charge exceeds a certain threshold,the scattering behavior of mesoscopic particles will change,which will affect the accuracy of particle optical measurement.When the particle size decreases from macroscopic to mesoscopic or even microscopic,the electrostatic properties of excess surface charges will gradually affect the optical properties of the particles.When the surface charges density exceeds the critical value,the scattering behavior of the particle will be dominated by the particle itself and its surface charges simultaneously.At this time,the measurement method based on the optical theory of electrically neutral particles is no longer applicable,which directly limits the reduction of the lower limit of the optical method.Therefore,the research on the optical properties of charged particles not only has outstanding practical significance for the realization of optical precision measurement,but also provides an indispensable theoretical basis for perfecting particle optical theory and exploring the interaction between charged particles and electromagnetic waves.This dissertation establishes scattering models for charged single particle,monodisperse particles and polydisperse particles respectively,and analyzes the scattering enhancement effect of surface charges on single particle and particle systems which scales in the submicron with mesoscopic characteristics.Based on the established light energy distribution model of charged particles,the forward scattering is taken as an example to analyze the enhancement effect of surface charges on the light energy distribution of particles.Through the measurement of particles with two properties and three distribution states,the enhancement effect of surface charges on the scattering of submicron particles is qualitatively verified.The specific research content of this dissertation is as follows:1.The complex refractive index model is extended to charged particles,generally applicable to electrically neutral particles and charged particles,and the mechanism of surface charges affecting elastic scattering is explained.There are discussed that the scattering characteristics of particles with different properties and the enhancement effects of the forward and backward scattered light intensity of the surface charges,taking Mie scattering of three typical dissipative particles as an example.It's determined that the particle diameter range and the surface charge density threshold in which the enhancement effect can be produced.2.A calculation model is established used to describe the light scattering characteristics of charged monodisperse and polydisperse particles,based on the Mie theory.The composite effects are considered of particle type,number,size distribution,complex refractive index,and surface charge on scattering.In terms of mechanism,it is explained why polydisperse particles have a buffering effect on the changes of various optical coefficients.The influence of the monodisperse degree of the particle system on the scattering enhancement effect is confirmed.3.The light energy distribution calculation model of charged monodisperse and polydisperse particles is established to realize the forward deduction of light energy distribution in the actual measurement process of charged particles.Take forward scattering as an example to discuss the enhancement effect of electric charge on scattering.It is confirmed that the particle size limit of the two kinds of measured particle samples with different properties in which the forward scattering enhancement effect can be produced.4.A qualitative experiment is designed to confirm the enhancement effect of surface charges on the light scattering of particles,through the discussion of the particle charged scheme and the charge measurement scheme,as well as the analysis of the charge dissipation mechanism.The measurement was carried out on three groups of submicron particle samples with different distributions to analyze the influence of the surface charge electrostatic characteristics on the measurement process,and qualitatively verify the enhancement effect of the surface charges on the light scattering.