Complexations Between Lonomers And Polyelectrolytes In Dilute Solution:A Molecular Dynamics Simulation Study

Due to their universality and unique physicochemical properties,ionomers and polyelectrolytes play essential roles in life science,industrial production,and theoretical research.Previous studies have shown that oppositely charged polymers can form ordered complexation structures through electrostatic interactions in solution.Although the complexation behaviors of charged polymers have been extensively studied for many decades,the deep understanding of the microscopic mechanism for such systems still remains challenging.In experiments,various factors are nonlinearly coupled,and it is difficult to study the cooperative effects of specific factors.Molecular dynamics simulation can be used to explore the influence of various factors on the properties of such systems at the molecule level,and help the understanding on the formation mechanism of the complex effects,which provides guidance for the design and development of new relative materials.In this dissertation,we use coarse-grained molecular dynamics simulation to study the complexation between ionomer and polyelectrolyte in dilute solutions.We explore the influence of electrostatic interactions and solvent effects on the structural properties of the aggregate formed by the ionomer and polyelectrolyte.Taking the vesicles assembled by the ionomer and polyelectrolyte as an example,we further study the deformation and break of the aggregates under the external electric field.The main contents of this dissertation are as follows:(1)Complexations between ionomer and polyelectrolyte in polar solvent:We study the complexation between ionomers and polyelectrolytes in polar solvents,systematically investigate the influence of the hydrophobic strength of ionomers’backbone and the intensity of electrostatic interaction between ion components on the structure of the complex,and further explain the molecular mechanism of the complexation process.Our research shows that the formation of the aggregates results from the short-range hydrophobic attractions between ionomers induced by the longrange electrostatic interaction between ionomers and polyelectrolytes,and the electrostatic interaction and solvent properties show significant impacts on the structure of aggregates.Our study on the dynamic process shows that due to the large size of aggregates,the movement speed in the system is slow.We analyze the system’s potential energy,and the results show the stronger electrostatic interaction between the ion components can cause the formation of stable aggregating structures.(2)Complexations between ionomer and polyelectrolyte in non-polar solvent:We study the complexation between ionomers and polyelectrolytes in non-polar solvents,systematically investigate the intensity of electrostatic interaction between ion components and the number of ionomers on the structure of polyelectrolytes,and further explain the molecular mechanism of the complexation effect changing the structure of polyelectrolytes.The results show that polyelectrolytes exhibit different structures in non-polar solvents with the change in the strength of ionic electrostatic interaction.By adding ionomers,the structure of the polyelectrolyte changes significantly.As the electrostatic is strong,the counterions adsorbed around the polyelectrolyte are replaced by the ionomers.The excluded volume of the ionomer backbone makes the polyelectrolyte chain show a stretched structure,and the scale of the radius of gyration with chain length exhibits an increase;As the electrostatic is weak,the poly electrolyte and the charged group of the ionomer are adsorbed with each other,resulting in the collapse structure and scale reduction of the chain under the electrostatic interaction.In the solution of multiple polyelectrolytes,the complexation between polyelectrolyte and added ionomer weakens the aggregation of polyelectrolyte and improves the polyelectrolyte solubility.(3)Deformation and break of complexed aggregates of polyelectrolyte and ionomers under an electric field:Taking the vesicles assembled by the ionomers and polyelectrolytes as an example,we further study the deformation and break of the aggregates under the external electric field.Our study shows that under the weak electric field,the vesicle undergoes a spherical-to-ellipsoidal transition.As the electric field strength increases,the ionic side-groups of ionomers are rearranged,and the ordered structure of the vesicle surface charge is wrecked,resulting in vesicle collapse.The collapsed vesicle further disassembles into ionomer clusters or tiny ionomer aggregates,which are uniformly dispersed in the solution.The collapsed vesicle further disassembles into ionomer clusters or tiny ionomer aggregations,which are uniformly dispersed in the solution.Our simulations clarify the mechanism for the breaking process of the ionic polymeric vesicle induced by electric field application on a molecular level.