2,929 research outputs found
Efficient sampling of reversible cross-linking polymers: Self-assembly of single-chain polymeric nanoparticles
We present a new simulation technique to study systems of polymers
functionalized by reactive sites that bind/unbind forming reversible linkages.
Functionalized polymers feature self-assembly and responsive properties that
are unmatched by systems lacking selective interactions. The scales at which
the functional properties of these materials emerge are difficult to model,
especially in the reversible regime where such properties result from many
binding/unbinding events. This difficulty is related to large entropic barriers
associated with the formation of intra-molecular loops. In this work we present
a simulation scheme that sidesteps configurational costs by dedicated Monte
Carlo moves capable of binding/unbinding reactive sites in a single step.
Cross-linking reactions are implemented by trial moves that reconstruct chain
sections attempting, at the same time, a dimerization reaction between pairs of
reactive sites. The model is parametrized by the reaction equilibrium constant
of the reactive species free in solution. This quantity can be obtained by
means of experiments or atomistic/quantum simulations. We use the proposed
methodology to study self-assembly of single--chain polymeric nanoparticles,
starting from flexible precursors carrying regularly or randomly distributed
reactive sites. During a single run, almost all pairs of reactive monomers
interact at least once. We focus on understanding differences in the morphology
of chain nanoparticles when linkages are reversible as compared to the well
studied case of irreversible reactions. Intriguingly, we find that the size of
regularly functionalsized chains, in good solvent conditions, is non-monotonous
as a function of the degree of functionalization. We clarify how this result
follows from excluded volume interactions and is peculiar of reversible
linkages and regular functionalizations.Comment: to appear in The Journal of Chemical Physic
Equilibrium properties of charged microgels: a Poisson-Boltzmann-Flory approach
The equilibrium properties of ionic microgels are investigated using a
combination of the Poisson-Boltzmann and Flory theories. Swelling behavior,
density profiles, and effective charges are all calculated in a self-consistent
way. Special attention is given to the effects of salinity on these quantities.
It is found that the equilibrium microgel size is strongly influenced by the
amount of added salt. Increasing the salt concentration leads to a considerable
reduction of the microgel volume, which therefore releases its internal
material -- solvent molecules and dissociated ions -- into the solution.
Finally, the question of charge renormalization of ionic microgels in the
context of the cell model is briefly addressed
- âŠ