| Due to the excellent mechanical property and diversity of polymer materials, a wide range of applications has been caused in various fields. Star polymers have extensive applications due to their important and particular features. Therefore, further studies on the structure and performance of the polymer materials are necessary. The research of the polymer chain movement is one of the core problem in polymer physics. There leaves many problems to be solved in the research of the dynamics and structural effect of the polymer in the confined condition. For the polymer translocation through a narrow channel or a nanopore, it is fundamental to the biological systems, examples including the transportation of DNA and RNA through nuclear pore complexes, motions of protein across membrane channels, and injection of viruses into the host cell nucleus. These researches can help us to deeply understand the complex transport processes and bring various potential technological applications, which are significant to the novel technology improvements, such as rapid DNA sequencing, gene therapy, controlling drug delivery, and designing nanopore sequencing device.Computer simulations can visualize these physical processes directly, which is effective to monitor the dynamic process in the confined condition. Computer simulation is neither experiment method nor theory method, which is based on the experiment through the basic principle, to construct the model and algorithm, and calculate the reasonable molecular structure and molecular behavior. With the development of computer hardware and the improvement of new simulation technology and model, computer simulation is playing a more and more important role in studying polymers.In Chapter3, We established two theories to describe the dynamics of the translocation process of linear and star polymers, that is the Nucleation and Growth Theory and de Gennes’s Blob Model. Both of them show linear relationship between the translocation time τ and the total number of beads Ntot and it makes good agreement with our simulation result of three arms star polymers. The translocation time τ, which is defined as the time that the chain moves through the nanpore channel completely in the direction of the fluid field, draws the most attention.In Chapter4, in the light of the above theory, We study the conformational changes and dynamic properties of star polymer chains during the translocation process accompanied by hydrodynamic interaction in three dimensions with the help of dissipative particle dynamics (DPD) simulation approach, focusing on the dependence of the translocation time on the polymer chain length and intermediate conformations, in order to captures the essential physical and chemical properties of the systems. DPD technique is a mesoscopic method that can well developed to describe the hydrodynamic behavior and correctly represents specific monomer/solvent interactions, which is an effective simulation method for understand the conformational and dynamic behaviors of polymer during the translocation processes. The influences of the chain length N and the chain conformations on the translocation time are evaluated. The translocation time scales with the total number of beads of star polymer as τ～Ntot1.09±0.04。Several different intermediate conformations are observed and they are closely related to the translocation time. We divide the whole translocation process into two stages. The dynamics in the first stage is similar to the nucleation. In the second stage, translocation time τ’ is weakly dependent on the forward arms fin and increases with the backward arms fout according to our theories and simulations. The above results demonstrate that the present of the hydrodynamic flow field, the chain length, and the topology properties exert considerable influence on the dynamic behaviors of star polymer during its translocation through a nanopore channel. |
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