Phase Behavior of Ionic Block Copolymers Studied by a Minimal Lattice Model with Short-Range Interactions

Abstract

We present the results of Monte Carlo lattice simulations of a model symmetric diblock copolymer wherein a fraction of segments of one block, p, corresponds to ionic species, and the other block does not contain ions. We use experimentally determined Flory−Huggins interaction parameters, χ, to quantify the interactions between ionic and nonionic monomers. Analysis of the experimental data indicate that χ between poly(styrenesulfonate) and polystyrene is about 5, a value that is orders of magnitude larger than that obtained in mixtures of nonionic polymers. Our model predicts that clustering of ionic monomers in the disordered state results in stabilization of the disordered phase and the product p 2 χN is well above the mean-field value of 10.5 at the order−disorder transition (N is the total number of monomers per chain). Network morphologies and hexagonally packed cylinders are observed in the ordered state at large p values while more traditional lamellar phases are found at small values of p.

Self‐Assembly of Poly(vinylpyridine‐b‐oligo(ethylene glycol) methyl ether methacrylate) Diblock Copolymers

“…There have been several different approaches to modeling the phase behavior of low dielectric constant block copolymers with salt or charge, which have resulted in different predictions for the expected phase behavior. Knychala et al used a Monte Carlo simulation approach where six χ parameters were defined between three different monomers (two uncharged, one charged) with the highest values of χ between the charged and uncharged monomers; they found that the effective interaction depended on the square of the fraction of charged monomers ( p ) and that the strong segregation regime was dominated by lamellar phases caused by a high degree of chain stretching ( p χN values of 40 and above for the compositions studied here), inconsistent with our experimental observations. Goswami et al and Sing et al both developed approaches that account for Coulombic interactions: Goswami using an explicit Coulomb potential in a Brownian dynamics simulation and Sing by using a coupled liquid state and self‐consistent field theory simulation.…”

“…Brownian dynamics simulations of a block copolymer where the charged block accounts for 25% of the component monomers match the results of the field theory simulations when the dielectric constant is low; however, for high dielectric constant materials, increased charge promotes phase mixing . Lattice Monte Carlo simulations for symmetric diblocks show the presence of cylindrical, gyroid, hexagonally perforated lamellar, and lamellar phases depending on the degree of charge, the value of χ , and the overall chain length …”

Cubosomes from hierarchical self-assembly of poly(ionic liquid) block copolymers

“…The controlled addition of water to a THF solution of PAA- b -PIL generated conditions where the hydrophobic PIL block became insoluble while the PAA block was still soluble, and the polymers started to aggregate to form centric multilamellar structures. The lamellar particles had low degree of long range order, which might be attributed to the strong segregation between the ionic and nonionic blocks66. On the other hand, the bulky asymmetric structure and charge delocalization of the imidazolium ring and non-coordinating Tf 2 N − led to large anion-cation distance, weak electrostatic interaction, and thus the short range anion-cation ordering was expected to be low67.…”

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.…”