Rigid Effect Of Middle Block On Physical Gelation In Triblock Copolymer Solutions: A Monte Carlo Simulation

Polymer gel exists in our lives widely because of their widespread industrial applications,such as rubber products,contact lenses,human skin cells,dual-core phospholipids membranes, etc. Some new research methods should be introduced , We use Monte Carlo simulation and change persistence lengths to investigate the structure and properties of physical gelation in polymer solutions in this thesis, all of which have important scientific significance and potential value.Once polymer chains cross-linked,either chemically or noncovalently, they lose their individual identity and become part of a large three-dimensional interconnected network pervading through the entire solution volume. The polymeric gels can be divided into chemical gels which are cross-linked by covalent bond through the irreversible gelation processes, and physical gels which are trapped by physical interactions such as van der Waals interaction, electrostatic interaction, hydrophobic force and hydrogen bond etc., formed through reversible physical gelation processes. Polymeric gels have attracted a lot of attentions in recent years because of their unique mechanical properties and strong response to temperature, pressure, electric current, and magnetic field.The flexibility of the polymer chain can strongly influence the nature of polymer solution, and the behavior of Physical Gelation is rooted in the nature of polymer solution, so chain flexibility may become an important factor during physical gelation.However,chain flexibility may be often ignored in theoretical and simulation research work( most researchers consider polymer chains as completely flexible),but we know that different polymer chain has its own persistence length(Persistence length is a characteristic parameter that can describe the elastic properties and the chain flexibility of both synthetic and natural polymers.).I think it is necessary to study the effects of chain flexibility on polymer gelation in order to reveal the structure and rheological properties of polymeric gels .because we do not know that whether polymer solution or not is his real system under ignoring chain flexibility conditions?We use improved eight-site bond fluctuation model to study polymer solution, and prove this model right by scaling relationship between mean-square end-to-end distance < R2> and chain length N. At the same time,we use this model to study rigid effect on physical gelation in copolymer solution using Monte Carlo simulation.The result of specific research as follows:(1). I get the plot of the chain conformation changing with chain flexibility by Monte Carlo simulation in polymer dilute solution,its concentration is 0.05. Monte Carlo simulation is performed in a cubic lattice ,which volume is 200 3,N is the number of monomer ,which varies from 10 to 200.The system consists of a polymer A[N].All the interactions are null except that the interaction pairs between the monomer in polymer chains and the solvent molecule have an attractive potential of -0.1kBT.Two monomers can interact only when distance between them is no more than 6 ,which ensure that first peak of correlation function is encompassed within the range of potential.All the polymer chains and solvent molecules are evenly dispersed in the simulation lattice,each monomer of polymer chains has trial to move 5×105MCS(Monte Carlo Steps)without any interactions ,and again run 2×106MCS under thermodynamic equilibrium.All of the simulation results are collected from parallel samples under thermodynamic equilibrium.The system was equilibrated through motion of bond-fluctuation model.The attempted relaxation motions were realized by the random diffusion of any monomer of polymer chain,The relaxation must be governed by Metropolis principle and persistence length restrictions.In summary,our results show that Rh∝Rg∝RF∝Nν((νeaqul to0.588)under different persistence length.at the same time ,we get the plog of the dependence of the Rg/Rh and Rg/RF on lp/Nc .(2).I also simulate that rigidity produces an effect on sol- gel transition. Monte carlo simulation is performed in a cubic lattice ,which volume is 1283 with periodic boundary conditions in all directions,N is the number of monomer ,which is 50.The system consists of a polymer A5B45A5, Interactions between monomers is–0.8kBT,the rest interactions is 0.Two monomers can interact only when distance between them is no more than 6 ,which ensure that first peak of correlation function is encompassed within the range of potential.All the polymer chains and solvent molecules are evenly dispersed in the simulation lattice,each monomer of polymer chains has trial to move 5×105MCS(Monte Carlo Steps)without any interactions ,and again run 2×106MCS under thermodynamic equilibrium.All of the simulation results are collected from parallel samples under thermodynamic equilibrium. The system was equilibrated through motion of bond-fluctuation model.The attempted relaxation motions were realized by the random diffusion of any monomer of polymer chain,The relaxation must be governed by Metropolis principle and persistence length restrictions,I improve chain flexibilities by changing the angle between neighboring B bond vectors in polymer chains ,while A is soft completely.by this way ,we will understand how persistence lengths produce an effect on sol- gel transition.In this system,results show that the bigger rigity gets, the lower sol-gel transformation concentration gets. At the same time, The populations of the chains with different conformations illuminate that micelles get togther by bridge chain,so cluster size will get big to percolate rapidly before gel formation;The loop conformations dominate the micells growing after after gel formation.