Simulation On Dynamics Of Confined Polymers Under Flow

Due to its fundamental and practical importance, polymer behaviorunder confinement condition has long been an interesting research. Bothbiological polymer and synthetic polymer are under geometric constraintand tangle topologic constraint. On the one hand, geometric confinedpolymers are widely present in organisms, microflow design and porousmedium. On the other hand, as the actin form a dense net in eukaryoticcells, single actin fiber’s behavior closely relates to tangle.With the deep understanding of polymer equilibrium properties,more and more researches turn their attention to the non-equilibriumdynamics. As the biological polymer always in non-equilibrium state inliving cells, the processes are finished by biological polymernon-equilibrium dynamics in cell. Moreover, almost all of the biologicalpolymer dynamics proceed in flow. What’s more, the manufacture of thesynthetic polymer, such as mechanical process, welding, splicing,extruding, blowing, injection and so on, are completed in the flowage. So,the rheological properties of biological polymers and synthetic polymershave guiding significance to the biological process and polymerprocessing technology.In our thesis, we focus on two systems——dilute polymer solutionand polymer melt in steady shear by non-equilibrium molecular dynamicsand multi-particles collision dynamics to improve efficiency. The main results are as follows:(1) The polymer dynamic behavior in both uniform shear flow andPoiseuille flow has been studied by multi-particles collision dynamicssimulation method. We find that the behavior of the single chain inPoiseuille flow is the same to the one in the uniform shear flow. Both ofthem present sketching-orientating-recoiling-tumbling movement incircle. The chain moves to the center mainly due to the hydrodynamicinteractions between the wall and the polymer.(2) By using the multi-particles collision dynamics, we have studiedthe structural properties and dynamics behavior of the polymer absorbedon the surface both in the equilibrium and in the non-equilibrium. It isfound that the diffusion coefficient of the polymer in equilibrium issubject to the influence of surface roughness, but the radius of gyrationhas not been affected by the characteristic of the surface. The polymerwill sketch along the direction of vorticity in the small ratio, but willsketch along the flow in the large shear ratio. The different strength ofabsorption and the shear ratio, the different migration ratio of the chain.The chain will migration faster in the large shear ratio and weakerstrength of absorption. The above results demonstrate that the present ofabsorption surface has important influence on both the structuralproperties and the dynamic behavior.(3) By the non-equilibrium molecular dynamics method, we focus on the polymer melts’ scaling of shear viscosity, the first normal stressand the second normal stress with the shear ratio at the steady shear. Weobserved the shear thinning phenomenon in simulation of three differentchain lengths. Meanwhile, we found that with the increasing shear ratio,the first normal stress increased slowly at the beginning, but increasedrapidly after the critical shear ratio. Different is that the first normal stressis relevant to the length of chain, but the second normal stress isindependent of the length of chain.