[SY-N7] Simulations of Branched Polyelectrolytes
Polyelectrolytes (PEs) are polymers with ionizable groups. Under suitable conditions, PEs are soluble in aqueous media. This property makes them attractive for biological, medicinal and environment-friendly applications that require organization of matter at nanoscale. The applications of PEs range from drug carriers, water pollutants removal, oil recovery to sea water desalination. In some of them, e.g. as thickening agents or super-absorbents in diapers, they have already reached mass production.
In this contribution a general and efficient simulation technique based on hybrid Monte Carlo (HMC) method will be described. HMC uses dynamics for evolution, but dynamics of a long polymer with N beads is itself slow (Rouse time ∝N2). For this reason we use a faster unphysical evolution with a modified Hamiltonian while still efficiently Monte Carlo sampling the Boltzmann distribution with the original one. The resulting simulation is much faster than molecular dynamics and other methods. It is
also well suited for simulations of coarse-grained models of PEs and allows for using reaction and other ensemble [F. Uhlik et al. Macromolecules 47 (2014) 4004].
Results for several types of branched PEs (e.g., stars and combs) for different conditions of solvent quality, Bjerrum and Debye lengths will be given. While strong PEs remain fully ionized, the degree of ionization of weak PEs can be influenced by both changing pH and ionic strength. This results in a responsiveness to external stimuli needed in many applications. The conformations of weak PEs are coupled with charge redistribution and this can lead to unexpectedly complex behavior. For example, strong PE stars in marginally poor solvents form bundles while weak PE stars redistribute charge and form core-shell structures with some arms uncharged and collapsed and others charged and extended. Behavior of other branching types as well as formation of inter-polyelectrolyte complexes will be also discussed.
In this contribution a general and efficient simulation technique based on hybrid Monte Carlo (HMC) method will be described. HMC uses dynamics for evolution, but dynamics of a long polymer with N beads is itself slow (Rouse time ∝N2). For this reason we use a faster unphysical evolution with a modified Hamiltonian while still efficiently Monte Carlo sampling the Boltzmann distribution with the original one. The resulting simulation is much faster than molecular dynamics and other methods. It is
also well suited for simulations of coarse-grained models of PEs and allows for using reaction and other ensemble [F. Uhlik et al. Macromolecules 47 (2014) 4004].
Results for several types of branched PEs (e.g., stars and combs) for different conditions of solvent quality, Bjerrum and Debye lengths will be given. While strong PEs remain fully ionized, the degree of ionization of weak PEs can be influenced by both changing pH and ionic strength. This results in a responsiveness to external stimuli needed in many applications. The conformations of weak PEs are coupled with charge redistribution and this can lead to unexpectedly complex behavior. For example, strong PE stars in marginally poor solvents form bundles while weak PE stars redistribute charge and form core-shell structures with some arms uncharged and collapsed and others charged and extended. Behavior of other branching types as well as formation of inter-polyelectrolyte complexes will be also discussed.