Structure formation in films of weakly charged block polyelectrolyte solutions

Abstract

A mean-field dynamic density functional theory is used to describe a phase diagram of concentrated solutions of weakly charged flexible block polyelectrolytes in a film. Electrostatics is taken into account by applying the local electroneutrality constraint (the Donnan membrane equilibrium approach). In the Donnan limit it is assumed that a salt added to the solution perfectly screens long-range electrostatic interactions. The phase diagram of a solution of a triblock polyelectrolyte in a film as a function of the solvent concentration and the charge of the polyelectrolyte (solvophilic) block is calculated for a given film thickness. The phase behavior of the block polyelectrolyte film arises from the interplay between surface-induced alignment and the electrostatically-driven structure formation. The observed mesoscopic structures (lamellar, perforated lamellar, cylindrical, micellar, and mixed phases) are oriented parallel to the surfaces for the considered case of morphologies unfrustrated by the film thickness. Structures with connections between parallel layers (bicontinuous, etc.) are not formed. As a result of surface-induced ordering, the region of ordered phases in a film is wider than in bulk and the phase boundary between ordered and disordered phases is more diffuse. As in the case of unconfined block polyelectrolyte solution, the solution in a film does not follow the lyotropic sequence of phases of such a block copolymer upon increase in the charge of the polyelectrolyte block. Upon changing the charge of the solvophilic copolymer block, transformations of copolymer morphology take place via change in curvature of polymeric domains. Due to confinement of a polyelectrolyte film, no swelling of solvophilic domains is observed.

Microphase separation in polyelectrolytic diblock copolymer melt: Weak segregation limit

“…A number of researchers have tried to explore charged diblock systems. Some of these efforts are invested in studying dilute solutions (micelle regime) 20, 23 and others have been carried out in the concentrated regime 3,4,5,24,25 . The fundamental question is how Coulomb interactions affect the relative stabilities of ordered morphologies.…”

Predicting the Morphology of Metallo‐Supramolecular Block Copolymers with Bulky Counter Ions

“…[22][23][24] The metallo-supramolecular copolymer was modeled as a triblock polyelectrolyte ABC with two neutral (A and C) and one polyelectrolyte (B) block. The PS 20 -[Ru]-PEO 70 metallo-supramolecular copolymer was represented as A 6 B 2 C 9 Gaussian chains with different beads A (PS), B (MLC), and C (PEO), whereas a bulky (BPh 4 ) counter ion was regarded as a single charged bead D. The molecular architecture of the PS 20 -[Ru]-PEO 70 chain was chosen to mimic the relative length of each block of the PS 20 -[Ru]-PEO 70 metallosupramolecular copolymer in the experiments.…”

“…Each polymer bead in the Gaussian chain represents a number of monomers. [22,23,25] On the basis of the experimentally estimated diameter d MLC ¼ 1.49 nm of a MLC with two (BPh 4 ) counter ions, which was obtained assuming a close-shell packing of the metal complex and the counter ions, [1] and the statistical segment lengths a PS ¼ 0.68 nm [26] and a PEO ¼ 0.28 nm [27] of the PS and PEO Gaussian chains, the period of a lamellar structure was found to be around 11.8 nm. In the present simulations, all the beads have the same size, so the relative lengths of the blocks in the A 6 B 2 C 9 chain are close to those of the experimental system.…”

“…[22,23,25,[28][29][30][31] The intrinsic chemical potentials m i : dF[r i ]/dr i are defined as the functional derivatives of the free energy F. The free energy F of a block copolymer system is that for a compressible melt consisting of Gaussian chains in a mean-field environment. The free energy functional and the intrinsic chemical potentials include extra terms as a result of electrostatic interactions.…”

“…A mean-field dynamic density functional theory (DDFT) for charged systems [22][23][24] is utilized to mimic the phase behavior and kinetics of the phase separation observed in recent experiments on a PS 20 -[Ru]-PEO 70 copolymer with (BPh 4 ) counter ions. [1] The metallo-supramolecular copolymer is modeled as a triblock polyelectrolyte with two neutral outer blocks (PS and PEO) and one polyelectrolyte middle block (the MLC).…”