The formation of ordered nanostructures in block polyelectrolyte systems is governed by the interplay between electrostatic interactions and chain conformational entropy. In this study, we investigate the phase behavior of diblock copolyelectrolytes driven by complex coacervation, focusing on how ion pairing dynamics influence self-assembly pathways. Our theoretical framework extends the self-consistent field theory (SCFT) to include reversible ion pair formation between oppositely charged monomers and between charged monomers and counterions. The strength of these associations is controlled by two parameters: Kaa, representing the binding affinity between A1 and A2 blocks, and Kac, reflecting the interaction between charged monomers and small ions. By systematically varying these parameters, polymer concentration, and salt content, we construct detailed phase diagrams that reveal the intricate balance governing microphase separation.
Our results demonstrate that Kaa acts as a primary driver for phase separation. As Kaa increases, the free energy of ordered phases decreases, leading to larger domain sizes and sharper A–B interfaces. This reflects enhanced segregation due to strong electrostatic pairing between opposite charges. Spatial distributions show that A1 monomers become enriched in A-rich domains while C1 ions are depleted there, consistent with preferential pairing of A1 with A2 over C1. However, increasing Kac has the opposite effect: it suppresses phase separation by promoting ion pair formation between A1 and C1, thereby reducing the availability of charged sites for inter-block association. This leads to a more homogeneous distribution of A1 monomers and higher concentrations of free C1 ions across both domains. The competition between Kaa and Kac is further modulated by salt concentration, which screens electrostatic interactions and reduces the stability of ion pairs, particularly [A1–A2]. Consequently, high salt levels favor disordered states, even at elevated polymer concentrations.
We observe that the product of salt concentration and Kac behaves as a single control parameter, allowing us to collapse multiple phase diagrams into a normalized representation. This finding suggests that the effective ionic environment—rather than salt concentration alone—determines phase morphology. For symmetric systems (fA = 0.5), four distinct ordered phases emerge: body-centered cubic (B1), hexagonal cylinder (H1), lamellar (L), and reverse body-centered cubic (B2). At low polymer concentrations, only B1 and H1 phases are stable.HSPA1A Antibody web As p increases, L appears, followed by B2 at high p and moderate salt. Notably, re-entrant transitions are observed—such as B1 → H1 → B1—when salt concentration is increased at fixed polymer density, indicating complex non-monotonic behavior arising from competing entropic and energetic effects.
The composition of the charged block also plays a crucial role. When fA = 0.3, only B1 and H1 phases are stable, suggesting that minor charged components cannot support large-scale ordering. As fA increases to 0.5, the L phase emerges, and its stability window expands.53-86-1 Synonym At fA = 0.PMID:35092153 7, the system exhibits a rich sequence of transitions: B1 → H1 → L → H2 → B2, mirroring the phase behavior seen in neutral block copolymers when block ratio is varied. This indicates that the relative volume fraction of charged blocks controls the curvature and symmetry of self-assembled structures. Moreover, our predictions align qualitatively with experimental data from Krogstad et al. and Kim et al., where similar phase sequences were observed in triblock systems under comparable conditions.
In summary, this work establishes a predictive model for coacervate-driven self-assembly in block polyelectrolytes by incorporating ion pairing dynamics. It reveals that microphase separation is not solely determined by χ parameters but is instead governed by a delicate equilibrium among charge association, counterion release, and screening. The ability to tune phase behavior through Kaa, Kac, salt, and composition offers powerful design principles for functional nanomaterials. The model’s agreement with experimental trends underscores its utility in guiding future synthesis and characterization efforts.MedChemExpress (MCE) offers a wide range of high-quality research chemicals and biochemicals (novel life-science reagents, reference compounds and natural compounds) for scientific use. We have professionally experienced and friendly staff to meet your needs. We are a competent and trustworthy partner for your research and scientific projects.Related websites: https://www.medchemexpress.com