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Title: Computer simulation of tracer diffusion in gel network
Authors: ZHOU HUAI
Keywords: computer simualtion, tracer diffusion, polyelectrolyte gel,mesoscopic scale
Issue Date: 24-Apr-2009
Citation: ZHOU HUAI (2009-04-24). Computer simulation of tracer diffusion in gel network. ScholarBank@NUS Repository.
Abstract: Computer simulation is used to study tracer or chain diffusion in polyelectrolyte gels. Owing to the limitation of present computer power, a mesoscopic approach is adopted to handle long time dynamics in this thesis. Brownian Dynamics (BD) simulation is mainly employed to study the self-diffusion of tracer particles and polymer chain in a cross-linked gel network based on a coarse-grained bead-spring lattice model with a truncated Lennard-Jones potential representing the excluded volume effect and a screened electrostatic interaction accounting for charge effect. Several effects are investigated including the network porosity, flexibility, degree of cross-linking (for tracer particle diffusion only), and electrostatic interaction. In addition, Dissipative Particle Dynamics (DPD) method is implemented to examine hydrodynamic interaction for tracer diffusion in gel network that is ignored by BD simulation. For tracer particle diffusion, the long-time diffusivity of tracer particle is studied in both uncharged and charged system. It is interesting to find that for charged system the diffusion is further hindered by the electrostatic interaction, regardless of whether the tracer particle and the network are oppositely or similarly charged. However, there exists a difference in the hindrance mechanism between the two cases. For the polymer chain diffusion, the conformation and dynamic properties of polymer chains are examined. For uncharged system, a decrease in diffusivity of chain is observed with the decrease of the porosity of the network. The difference in diffusion behavior of an oppositely and similarly charged chain in gel network is discussed for varied charge amount or Debye length. The static properties of the chain are used to explain the difference between the two cases, such as the average bond angle, the mean-square end-to-end distance, the mean-square radius of gyration, and the three average eigenvalues of the moment of inertia tensor. Finally, the applicability of the DPD method to study the hydrodynamic interaction for the tracer diffusion in gel network is demonstrated, and the advantages or disadvantages of the DPD and BD method are also addressed. These computer simulation results based on the simplified coarse-grained model shed light on the diffusion behaviour of a tracer particle or chain at mesoscopic level. The unusual behaviour of tracer or chain caused by the attractive electrostatic force is intriguing, which can be explained by electrostatic entrapment effect. This effect is dependent on the charge, double layer thickness, and porosity.
Appears in Collections:Ph.D Theses (Open)

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