Theoretical Studies Of Diffusion Dynamics In Confinement,Porous And Active Environments

With the development of life and nanotechnology science,the diffusion dynamics in mesoscopic scale(Generally,the range of mesoscope is 10nm?1?m)gained more and more attentions due to its significance.Generally,mesoscopic systems have very complex inner structures and motion characteristics(such as cells,ion channels)which lead to many interesting dynamics behaviours,such as particle directional transport,polymer anomalous diffusion and phase separation of colloids.We need to use the appropriate models combining with theories to simulate and study such issues because they cannot be described and analyzed by simple statistical physical equations.In the present paper,we use the theory combining with simulation to study the influence of complex environments such as confinement,porous and active particles on the diffusion dynamics of nanometer substances.?Particle diffusion dynamics in confined spacesIn the last three decades,the studies of particle diffusion in confined space always are the frontier issues of physcial,chemical and living science fields due to their importance and applications in real mesoscopic systems.In soft condense and living systems,the substances must arrive to specific places to realize some special functions by traversing the narrow and long channels.In the present paper,we mainly focus on two important dynamics behaviours of nanoparticles in time-changing channels,entropic stochastic resonance and particle directional transport.The results demonstrate that the intensity of stochastic resonance and the velocity of particle directional transport both depend on gravity non-monotonically,such phenomena cannot be observed in static channels.By using the coarse-grained description,we find that an effective entropic force was exerted on the particles.Furthermore,we have studied the influence of other physical quantities on the entropic stochastic resonance and particle transport,such as oscillation amplitude,frequency,phase lag,asymmetry.?Polymer diffusion dynamics in complex environmentsThere are vast substances in complex environments,such as actin fibers,ribosomes,t-RNAs and m-RNAs.These substances would affect the diffusional and structural dynamics of macromolecules dramatically.For example,the obstacles therein could reduce the activity of enzymes,stabilize RNAs and hinder the movement of DNA-binding proteins.And the studies of diffusion of macromolecules in complex environments with a mass of substances are one of the important issues in biological physics and chemistry.In the present paper,we have studied the diffusional and structural dynamical behaviours of macromolecules in porous media by combining the mode-coupling theroy and generalize langevin equation.It is found that macromolecules have an anomolous diffusion and the power-law relaxtion of end-to-end distance fluctuation auto-correlation in porous media.We also find that existence of matrix particles is the main reason which lead to the subdiffusion of macromolecules.?Nonequilibrium dynamics in active particle systemsActive particles are synthetic nanoparticles which could transform the surrounding energy to the driven force to make the particles move directionally.In recent years,various active particles have been prepared.Due to the non-equilibrium features of systems,the active particles systems could lead to many interesting phenomena,such as active swaring,larger scale vortex formation,phase separation,etc.,both experimentally and simulatively.Now,ones begin to study how the activity of particles influences the glass transition point,espeically the dynamics heterogeneity.In the present paper,we use the lagevin equation to simulate active particle systems in order to study systematically the influences of activity on the dynamics heterogeneity.We find that the degree of dynamics heterogeneity depends non-monotonically on the activity of particles,it also has a non-monotonical relationship with the volume fraction of particles under large activities.These non-trivial phenomena suggest that the activity of particles plays two roles in these systems:one is inducing a higher effective temperature,the other one is inducing an effective attractive interaction between particles.