Dissipative Particle Dynamics Study of the pH-Dependent Behavior of Poly(2-vinylpyridine)-block-poly(ethylene oxide) Diblock Copolymer in Aqueous Buffers

Abstract

The paper describes the pH-dependent selfassembly of a diblock copolymer, poly(2-vinylpyridine)-blockpoly(ethylene oxide), P2VP−PEO in aqueous media using computer simulations. We employed the dissipative particle dynamics (DPD) method and found that the copolymer with electrically neutral (i.e., deprotonated) or very low-protonated P2VP blocks form multimolecular spherical core−shell micelles with insoluble P2VP cores in neutral and alkaline solutions, while protonization (ionization) of P2VP blocks exceeding 25% provokes the dissociation of micelles in single chains in acidic media. The finding that a clearly pronounced transition occurs in a restricted pH region slightly above pK A ap (where pK A ap is the apparent dissociation constant of the conjugated acid P2VPH + ) is in good agreement with the experimental data (Macromolecules 1996, 29, 6071−6073). This suggests that (i) the tested model is reasonable and the mutual relationship between the parameters used in the soft repulsive and electrostatic potentials was set appropriately and (ii) the DPD method is a suitable simulation technique for studying phenomena accompanied by pronounced changes in the global properties of complex polymer and polyelectrolyte systems. Although we studied the behavior of only one specific system, the simulation yields a generic pattern for the pH-dependent self-assembly of copolymers containing one neutral water-soluble block and one annealed (weak) polyelectrolyte block with fairly hydrophobic backbone.

Dissipative Particle Dynamics Study of Electrostatic Self-Assembly in Aqueous Mixtures of Copolymers Containing One Neutral Water-Soluble Block and One Either Positively or Negatively Charged Polyelectrolyte Block

“…13 In a recent paper, we studied the pH-dependent selfassembly of a diblock copolymer formed by a PE block with a strongly hydrophobic backbone and a readily water-soluble block, namely the poly(2-vinylpyridine)-block-(ethylene oxide) sample using both soft coarse-grained repulsion and the Coulomb interaction potentials. 14 We obtained results that compare well with the experimental data, 15 suggesting that DPD simulations (when properly applied) yield a good prediction of the global features of general trends in the behavior of complex polyelectrolyte systems and provide an explanation for these features.…”

Modeling Aggregation of Ionic Surfactants Using a Smeared Charge Approximation in Dissipative Particle Dynamics Simulations

“…The smeared charge models have been applied to complex systems and phenomena, such as bulk electrolytes, individual polyelectrolyte molecules in electrolyte solutions, polymer brushes, polyelectrolyte translocation though narrow pores, hydrated polyelectrolyte membranes, peptides, and even dendrimer interactions with lipid bilayers. [13][14][17][18][19][20][21] Nevertheless, the predictive capabilities of the soft-core smeared charge models remain DPD studies of ionic surfactants using charge smearing have been quite limited. Very recently, Posel et al 17 tested the pH-dependent self-assembly of diblock copolymer using a Slatertype smearing charge distribution.…”

“…[13][14][17][18][19][20][21] Nevertheless, the predictive capabilities of the soft-core smeared charge models remain DPD studies of ionic surfactants using charge smearing have been quite limited. Very recently, Posel et al 17 tested the pH-dependent self-assembly of diblock copolymer using a Slatertype smearing charge distribution. In order to model the dependence of ionization on pH, the authors varied the charge of the hydrophilic block according to dissociation constant (similar approach was used earlier in DPD simulations of peptides 20 ).…”

Conformational transitions of a weak polyampholyte

“…One principal advantage of polyampholytes is that their association and stabilization behavior can be easily regulated by adjusting solution pH. This leads to many potential applications 5 and considerable interest in experimental, [33][34][35][36][37][38][39][40] theoretical, 2, 28, 41-45 and simulation [46][47][48][49][50][51][52][53][54][55][56] studies of polyampholytes. The conductivity, viscosity, as well as coil size of random polyampholytes have a minimum at the isoelectric conditions where there are equal numbers of positive and negative charges on the polymer backbone.…”