Self-Assembly of Partially Charged Diblock Copolymer-Homopolymer Ternary Blends

Ternary blends comprising a diblock copolymer and the corresponding homopolymers provide ready access to a variety of morphologies, but the impact of charge on their phase behavior has not been studied extensively. Here, three partially charged ternary blends consisting of symmetric poly[(oligo(ethylene glycol) methyl ether methacrylate-co-oligo(ethylene glycol) propyl sodium sulfonate methacrylate)] (POEGMA#), polystyrene (PS), and POEGMA#-PS with different charge fractions were prepared, where # denotes the mole fraction of charged monomers in the POEGMA chain. The phase behavior was systematically studied using small-angle X-ray scattering, and isothermal phase diagrams at 120 °C were constructed. The resulting isothermal planes contain a wide lamellar phase window with a slight deviation from symmetry for ion-containing ternary blends due to the homopolymer size difference. Given the absence of any significant change in the phase diagrams as the charge fraction increases, the role of charge is primarily to increase the segregation strength in the ternary system, as in the case of partially charged diblock polymers. In addition, examination of the increase in domain size along the volumetrically symmetric isopleth reveals a "dry-brush"-like swelling behavior of homopolymers in all three blends, presumably due to the space-filling nature of the oligomeric ethylene glycol side chains on POEGMA.