A Molecular Simulation Study Of The Dissolution Behavior Of Charged Polymers

Cellulose,chitin and polyelectrolytes have essential applied value.But the dissolution of these polymers has not yet been deeply understood.The structures of soft matters can not be described by traditional theories.Computer simulation,as a new research method,is not only an auxiliary of experiment,it can also find out new physical laws.In this paper,cellulose,chitin,and alkaline polyelectrolytes was studied in different solvents by all-atom or coarse grained simulations.The introduction of charged groups will greatly affect the solubility of the polymers.Only solvents with medium polarity can dissolve charged chains well.In addition,non-equilibrium simulations were used to study the conductivity of model polyelectrolytes.The uneven distribution of charge in the system significantly reduced its conductivity.In wet membranes,the conductivity of complete flexible chains was obviously higher than that of rigid chains,which indicates the tortuous water channel has a negative impact on ion conduction.The simulation results of these polymers are summarized as follows:1.Having broad applications,cellulose and chitin were the most abundant natural biological material resource on planet.We used all-atom molecular dynamics to study them in various solvents.Lithium ions on cellulose and sodium ions on chitin were found to be specifically adsorbed.Different dissolution process was inferred,according to their distributions and interactions.Cellulose contains only hydroxyl functional groups.Hydroxide ion,as a strong hydrogen bond receptor can be directly combined to hydroxyl,destructing hydrogen bonding network in cellulose.Due to the small size of lithium ion,it can enter insider gaps of cellulose,promoting the adsorption of hydrogen Oxygen,so lithium hydroxide dissolves cellulose better.In chitin,the amide group also involves the formation of hydrogen bonds,only by additional interaction of sodium ions with amide,can the hydrogen bond network be destroyed.Dissolved.By counting the net charge of their hydration layer,we can roughly judge the stability of the solution.2.Since solvents with medium polarity stretched a polyelectrolyte chain,we tried to dissolve a typical alkaline polymer electrolyte aQAPS using mixed solvents.Most water-miscible organic solvent mixtures can dissolve aQAPS.In MD simulation,we did not observe the stretch of chains,and by energy decomposition,we speculated the driving force derived from electrostatic repulsion,further salting out experiments confirmed the dissolution state of aQAPS.3.Experimental studies have found that with suitable water added in solvent,the ion conductivity of aQAPS membrane could be significantly improved.We simulated wet film systems with different solvents,DMF or water.It was found that phase separation only occurs in water.A solvent replacement process was also simulated,but the morphology of membrane did not change much.Another film with a different backbone also has a similar result.The construction of phase separation must be done before film formed,otherwise the film should be heated to glassy state so that phase separation could continue.4.Finally,we tried to construct a new aQAPS coarse-grained model with its full atomic information,the final structure can be directly compared with TEM photos,we found many bend in the water channels.The zigzag structure derived from the sulfone group.By changing different functional groups,we may find alkaline membrane systems more suitable for ion conduction.