Microphase Separation in Sulfonated Block Copolymers Studied by Monte Carlo Simulations

Abstract

The underpinnings of microphase separation in symmetric poly(styrenesulfonate-block-methylbutylene) (PSS−PMB) copolymer melts were examined by Monte Carlo lattice simulations. The main challenge is understanding the effect of ion pairs in the PSS block on thermodynamics. We assume that experimentally determined Flory−Huggins interaction parameters are adequate for describing intermonomer interactions. Our model does not account for either electrostatic or dipolar interactions. This enables comparisons between simulated and experimentally observed microphases reported by Park and Balsara [Macromolecules 2008, 41, 3678] without resorting to any adjustable parameters. The PSS block in both experiments and theory is partially sulfonated. We quantified the effect of sequence distribution on phase behavior by using alternating and blocky PSS chains in the simulations. Depending on temperature and sequence distribution, simulations show perforated lamellae, gyroid, and hexagonally packed cylinders in addition to the lamellar phase found in simple symmetric block copolymers that do not contain ions. This is driven by extremely repulsive interactions between styrenesulfonate monomers and the uncharged species in the melts. The symmetry of the microphases and the locations of the order−disorder and order−order phase transitions are in qualitative agreement with experimental observations.

Effects of compositional asymmetry in phase behavior of ABA triblock copolymer melts from Monte Carlo simulation

“…(12), as we demonstrated in ref. [35]. At high temperatures we observe a single broad peak, characteristic of a disordered phase, but as the T * is lowered the multiple and narrow peaks develop which indicates the onset of the ODT.…”

Effects of Blockiness and Polydispersity on the Phase Behavior of Random Block Copolymers

“…One example would be poly(styrenesulfonate‐ block ‐polymethylbutylene) in which a random selection of the polystyrene monomers are sulfonated. Experimental studies as well as Monte Carlo simulations have shown that this system displays interesting phase behaviors . It would be interesting to explore the phase behavior of random copolymers with a non‐Markovian sequence distribution.…”

“…Experimental studies as well as Monte Carlo simulations have shown that this system displays interesting phase behaviors. [5][6][7] It would be interesting to explore the phase behavior of random copolymers with a non-Markovian sequence distribution.…”

Simulation of Ionic Copolymers by Molecular Dynamics

“…Computer simulations of such copolymers are more demanding because of the long-range interactions which have to be included. Some studies suggest that a minimal lattice model without longrange interactions can be used in the case of ion-containing block copolymers [16][17][18][19]. In this model the Flory interaction parameter, χ, between blocks is replaced by an effective interaction parameter that accounts for ionic interactions.…”