The Structure And Diffusion Dynamics In Quasi-Two-Dimensional Colloidal Systems

Diffusion is a fundamental process ubiquitous in physics,chemistry,biology,and material sciences.The diffusion coefficient for the simplest case-the Brownian motion of a mesoscopic spherical particle in a Newtonian fluid-is well described by the Stokes-Einstein equation.In most practices,however,diffusion occurs in complex environments with dynamical structures and interactions.Examples include the diffusions of dopants in semiconductors,colloids in polymer matrices,biological molecules in cells,and defects in crystals.The relation between dynamics and structure is of fundamental importance for our understanding of various disordered materials,such as dense fluids,liquid metals,alloys materials,polymer solutions,grain,and colloids.Therefore,it is very meaningful and challenging to explore the relation between dynamics and structure and find a theory model that can quantitatively predict the diffusion coefficient of atoms or macromolecules in complex media.In this thesis,using the techniques of video microscopy and particle tracking,we systematically study the dynamic behavior of colloidal particles in complex media,both crystalline and disordered,in quasi-two-dimensional colloidal systems.In the first part of the thesis,the large polystyrene colloid particles are charged using the method of sulfonating polystyrene colloid particles with concentrated sulfuric acid.The charge of colloidal particles is tuned by varying the sulfonation reaction time and the proportion of concentrated sulfuric acid and the particles to be sulfonated.Both the charge of polystyrene colloidal particles and the distance between particles increase with the increase of sulfonation time within a certain time frame.Secondly,we study the diffusion of 200 nm probe particles with negative charge in a wide range of complex moving backgrounds,both five kinds of crystalline with different lattice constant and disordered,in quasi-two-dimensional colloidal systems.The relation between the dimensionless diffusion coefficient of probe particles and the two-body structural entropy was investigated.The previously proposed relations between the diffusion coefficient and the two-body structural entropy are tested,and it is found that none of previous modes can correctly describe the kinetic behavior of colloidal particles in complex media.A new scaling equation is proposed with consideration for the viscous friction from the solvent,which is absent in previous theoretical models,and this new universal law is verified by experiment and simulation for the first time.Finally,we introduce the relation between the dimensionless diffusion coefficient of 350 nm and 560 nm probe particles and the two-body structural entropy in a wide range of complex fixed media composed of strongly charged polystyrene colloidal particles,both crystalline and disordered,in quasi-two-dimensional systems.The previously proposed modes,which describing the relation between the diffusion coefficient and the two-body structural entropy,are tested,and it is shown that none of previous theoretical models can effectively describe current systems.The new formula proposed in chapter three is in good agreement with the experimental data and indicates that this new relation is also suitable for the probe particles in the fixed complex media.