The Effect Of Self-Propelling On Phase Transition In 2D Colloidal Systems

In this thesis, we study numerically the process of 2D phase transition in the mixtures of active and passive particles.We first introduce colloids, active particles, Kosterlitz-Thouless-Halperin-Nelson-Young theory and the criterion for 2D transition. In chapter two, we give an introduction to the progress in colloids and some interesting phenomenon in active systems, such as clustering, vortex, phase separation, and self-assembly.Then we introduce our model for simulation and results. In our model, the active particles are the same with passive particles except self-propelled forces. We calculate the orientational correlation function, the global bond orienta-tional order parameter and its susceptibility, and present the Temperature-Self-propelling phase diagram. We show that active particles enhance the additional fluctuations of the system. And the transitional points shift with the increasing number of active particles as well as self-propelling force. Self-propelling effects extend the range of the state between the isotropic liquid phase and solid phase. At last, we calculate the distributions of active and passive particles and the de-fects. It is found that two kind of particles distribute uniformly, and the defects decrease with decreasing of temperature.