The Structures And Dynamics Of Colloidal Systems In Energy Landscape And Mixed Systems

Colloidal systems have become one of the most ideal experimental models in soft condensed matter physics research,because their size is suitable for microscopic observation and the interaction between particles is easy to control.Traditional colloidal physics research mainly focus on the diffusion behavior of colloidal particles on smooth substrates,or on the structure and dynamic behavior of colloidal systems made of spherical particles.However,it is well-known that the environment in a colloidal system is usually complicated,and the atomic and molecular systems are usually consist of anisotropic,non-spherical particles.Therefore,the structure and dynamic behavior of(1)colloidal systems in complex environments and/or(2)colloidal systems of anisotropic particles,have gradually attracted the attention of more and more researchers.In this paper,we mainly study the structure and dynamics of colloidal systems in two kinds complex environments through physical experiments.We first design different energy landscape substrate as sample cells,and study the effects of energy landscape on the structure and dynamics of colloidal systems.The mixed model of isotropic spherical particles and anisotropic ellipsoidal particles was chosen as a model to study the evolution of the structure and dynamic behavior of the glass transition process as the area fraction increases.The main contents of the research and the results are summarized as follows:(1)Dynamics of colloidal system on energy landscape substrate.In this study,a layer of periodically ordered colloidal particles was fixed on a glass slide to provide a periodic energy substrate for the subsequently settled colloids.By changing the size of the underlying fixed particles to change the energy landscape,we found that the particles are tend to be confined to the local minimum of energy landscape on the substrate.This behavior results in a slower dynamics of the colloidal system,which is similar to the dynamics slowing in concentrated colloidal suspension.In addition,the chain-like cooperative rearrangement regions are inhibited by the energy landscape,and the dynamic heterogeneity of the system is weakened,which is very different from the enhancement of dynamic heterogeneity concentrated colloidal suspension.(2)Glass transition in a mixture of colloidal ellipsoids and spheresIn this study,we experimentally investigate the glass transition of a mixture of colloidal ellipsoids and spheres by video microscopy and particle tracking.Through the analysis of radial distribution function,Voronoi diagram and local order parameter,it is found that the ellipsoid can effectively inhibit the crystallization of spheres,and the structure of the system remains disordered when increasing the area fraction.For dynamics,the mean square displacement(MSD)and self-intermediate scattering function are calculated.We find the dynamics of the system slows down substantially when increasing the area fraction,and the relaxation time of the system increases rapidly and diverges close to the glass transition point predicted by the mode coupling theory(MCT).Moreover,we analyze the fast particles that participate in cooperative rearrangement regions(CRRs);the result shows that the shape,size and position of CRR are closely related to the existence of ellipsoids in the system.