Poly(styrenesulfonate)−Poly(diallyldimethylammonium) Mixtures: Toward the Understanding of Polyelectrolyte Complexes and Multilayers via Atomistic Simulations

Abstract

Explicit solvent all-atom molecular dynamics simulations of mixtures of poly(styrenesulfonate)-(PSS) and poly(diallyldimethylammonium) (PDADMA) polyelectrolytes at various salt (NaCl) concentrations are performed. We characterize the formed polyelectrolyte complexes (PECs) and relate the observed physical properties of PSS-PDADMA PECs to the properties found in polyelectrolyte multilayers (PEMs) made of the same compositions. Our results reveal a change in the way charges are compensated upon the addition of salt, namely from an intrinsic mechanism (polyanions pair with polycations) toward an extrinsic one (polyions pair with salt ions). The probability of the intrinsic compensating mechanism decreases from about 90% to about 60% when the salt concentration increases from 0.168 to 1 mol/L. The interaction energies of the ion-pairing follow the order of Na-Cl>PSS-Na>PDADMA-Cl=PSS-PDADMA. Furthermore, we investigate thoroughly the water distribution and study the hydration mechanisms in our system. Water is found to be homogeneously distributed inside our investigated systems, while we find a negligible difference between the hydration ability of (PDADMA þ Cl -) and (PSS þ Na þ ). This lack of asymmetric behavior demonstrates that the observed swelling-shrinking switch during the buildup of PEMs cannot be related to the hydration behavior, and we suggest that the presence of a substrate has to play a critical role. A further analysis of the water structure shows that the dielectric constant inside such mixtures is roughly 1 order of magnitude lower than in bulk water, and our determined values compare favorably with experimental measurements. Finally the diffusion of water molecules inside the PE mixtures is found to be 2 orders of magnitude slower than that in pure water.

Atomistic simulation of PDADMAC/PSS oligoelectrolyte multilayers: overall comparison of tri- and tetra-layer systems

“…Inspired by the considerations discussed above, we introduced several pioneering works on the fully atomistic simulation of OEs complexes 65 , monolayers 66 and bilayers 67,68 . The latter were obtained by following a simulation protocol that mimics the experimental LbL deposition method.…”

Potential of mean force and transient states in polyelectrolyte pair complexation

“…Examples include atomistically-resolved systems [23][24][25][26][27][28] as well as coarse-grained models [29][30][31][32][33][34]. In addition to detailed structural and topological insights into the final complexed state, those studies indicate that the primary driving forces of PE complexation for weakly-charged PEs arises as expected from electrostatic attraction.…”

Coarse-grained simulations of polyelectrolyte complexes: MARTINI models for poly(styrene sulfonate) and poly(diallyldimethylammonium)

“…2,3 and slightly modified in Ref. 4. For a final comparison, we chose the model and the simulations presented in Ref.…”

“…For a final comparison, we chose the model and the simulations presented in Ref. 4. In addition, we developed our own PSS and PDADMA atomistic models which are based on the generalized AM-BER force field (GAFF) 5 with the help of the acpype routine 6 and the ANTECHAMBER suite 7 .…”

“…In addition, we developed our own PSS and PDADMA atomistic models which are based on the generalized AM-BER force field (GAFF) 5 with the help of the acpype routine 6 and the ANTECHAMBER suite 7 . Using two atomistic force fields (GAFF and OPLS-AA) in combination with different water models was motivated by the reference atomistic OPLS-AA PDADMA and PSS approach 4 in presence of SPC/E water 8 instead of TIP3P or TIP4P water 9 as it was originally recommended 1 . Hence, for the mapping of the MARTINI CG scheme, we chose four different atomistic force field combinations: i) PDADMA/PSS (OPLS-AA) + SPC/E water (as in Ref.…”