Molecular Dynamics Simulation On Static And Dynamic Properties Of Comb Polymer In Solution

Taking advantages of their special physical and chemical properties, polymers have recently attracted great research interest. It is meaningful to investigate the conformation and dynamics properties of polymer solution in guiding the production and application of polymer materials.In this thesis, we investigate the static and dynamic properties of different topologies polymers by using Molecular Dynamics(MD) simulation method in solution.Polymers have very complex chain topologies, such as linear, comb-like and star-like. Linear polymers are quite similar to the comb-like polymers with long backbones but very short side chains. Star polymers are comparable to comb-like polymers with long side chains but very short backbones. Comb-like polymers can be considered as a tie polymer connecting linear and star-like polymers, which are good model polymers to reveal the relationship between polymer properties and chain topologies. In order to further analyze the property dependence on the chain topology, we investigated the dendrimer polymers which have more branched and more complex side chains. The main results are as follows:1. We studied the static and dynamic properties of linear, comb-like and star-like polymers by using molecular dynamics method. We found star-like polymers had the smallest size, and linear polymers had the largest size at the same chain length. Changing the chain topologies from linear to comb-like and star-like will lead to the great change of scaling relationship of radius of gyration on both the degree of polymerization and the number of side chains or the arms. For star polymers, the increase of the number of arms results in the decrease of the radius of gyration and increase of the diffusion coefficients. Moreover, the scaling relationship for radius of gyrations for star-like polymers and comb-like polymer is also obtained. These results may help people understand the physical insight of the topological structure dependence on the static and dynamic properties of polymer chains.2. We performed simulation on the static and dynamic properties of comb-like polymers in solution. Comb-like polymers are densely grafted polymers, with properties distinctly different from those of sparsely grafted or linear polymers. Bulky side chains are packed around the backbone, and the steric effect between neighboring side chains forces the backbone to adopt a stretched conformation. Comb-like polymers can adjust to the structure and size via changing the grafting density, and the length of backbone or side chain.In this work, we mainly investigated the impact on the static and dynamic properties of comb-like polymers, by changing the grafting density and the number of grafted side chains. We found, at different grafting density, the degree of polymerization has a similar impact on the molecular size, but the impact of side chain on the molecular size is increased with the increase of grafting density. Moreover, the radius of gyration of polymer decreased with increasing the number of side chains at the same degree of polymerization and the same numbers of grafting points. The radius of gyration decreased with increasing the numbers of side chain at the same numbers of grafting points. The degree of decrease increased with increasing the grafting density. All the studied comb-like polymers with different numbers of side chains have a similar diffusion behavior at the same grafting density. When the grafting densities are different, comb-like polymers with various numbers of side chain also have a same diffusion behavior, i.e., the diffusion coefficient decreased with increasing the degree of polymerization. The impact of degree of polymerization on the diffusion of comb-like polymers with different numbers side chain is similar, but different numbers of side chain will cause the difference of diffusion behavior.3. Structural and dynamical properties of dendrimer polymer in solution are studied by using molecular dynamic simulation. Dendrimer polymers could be applied as a typical polymeric material, which has nearly perfect molecular structure and high geometrical symmetry, strictly controlled and gradually formed by multifunctional monomer and forming a highly branched structure macromolecules. Based on the peculiar rheology behaviour offered by dendrimer polymers, it is expected that dendrimers will be extensively used as biomedical devices, gene therapeutics, optical-electronic materials and so on. It is of great importance to study the static and dynamics properties of dendrimer polymers. In this work, we investigated dendrimers’ static properties and dynamics behaviour by molecular dynamics simulations and compared with corresponding linear polymers. It is shown that both a dendrimer and a linear polymer behave as an ellipsoidal shape, and the shape of dendrimers is thick ellipsoid. The size of dendrimer is smaller than linear polymer at the same degree of polymerization. Similar molecular topology of dendrimer has a close scaling law to the linear one. With increasing degree of polymerization, the diffusion coefficient and the random motion capability decreased. For dendrimers, the random motion capability is higher than the corresponding linear polymers.