Molecular Dynamics Simulation Of The Response Of Star Polyelectrolyte Brush To An External Electric Field

Compared with linear polyelectrolyte brushes,star polyelectrolyte brushes have a unique topology and more terminal monomers.As the brush graft density and the number of arms increase,internal stratification within the star brush layer emerges.The unique layering phenomenon results in the collapse of a fraction of grafted star chains near the grafted substrate,so the substrate can carry more acidic or basic functional functional groups,which is more conducive to regulating the hydrophilicity of the grafted surface,adsorption.Therefore,it can be used to fabricate bionic lubricants to improve interface lubricity.In this work,the author uses Langevin Molecular Dynamics simulation method to study the effects of different conformational parameters(arm number,arm length,average charge fraction)and different applied electric field on the conformations of star polyelectrolyte in a good solvent environment.The brush conformations and stratification are quantitatively discussed in terms of the brush average height,the overall probability density distribution,etc.in response to an external electric field.At present,people's research on charge reversal mainly focuses on free polymer chains,and we focused on the conditions and influencing factors of charge reversal of the grafting electrode by the polyelectrolyte star brushes and polyampholyte star brushes under the collapsing electric field.It was found that to induce charge reversal,the total number of charged monomers on a single grafted ordinary polyelectrolyte polymer chain or the total net charge on an amphoteric polyelectrolyte polymer chain must exceeds a certain number,and this number varies with the Bjerrum length in a decreasing fashion.The simulation results show that the thickness of the adsorption layer is basically independent of the number of arms of the star chain,the charge fraction and the arm length.The degree of charge overcompensation(the degree of the charge reversal)increases with the increase of the charge fraction.At the same time,when the Bjerrum length is large,the polyelectrolyte brush gradually shows a neutral brush characteristic,and the degree of charge overcompensation gradually decreases.That is to say,the functional relationship between the degree of overcharge compensation and the Bjerrum length is non-monotonic.