Abstract
Charged block copolymers are of great interest due to their unique self-assembly and physicochemical properties. Understanding of the phase behavior of charged block copolymers, however, is still at a primitive stage. Here we report the discovery of an intriguing superlattice morphology from compositionally symmetric charged block copolymers, poly[(oligo(ethylene glycol) methyl ether methacrylate–co–oligo(ethylene glycol) propyl sodium sulfonate methacrylate)]–b–polystyrene (POEGMA–PS), achieved by systematic variation of the molecular structure in general, and the charge content in particular. POEGMA–PS self-assembles into a superlattice lamellar morphology, a previously unknown class of diblock nanostructures, but strikingly similar to oxygen-deficient perovskite derivatives, when the fraction of charged groups in the POEGMA block is about 5–25%. The charge fraction and the tethering of the ionic groups both play critical roles in driving the superlattice formation. This study highlights the accessibility of superlattice morphologies by introducing charges in a controlled manner.
Highlights
Charged block copolymers are of great interest due to their unique self-assembly and physicochemical properties
Several recent reports have been directed toward unveiling the thermodynamics and self-assembly of ioncontaining block copolymer systems, including both salt-doped block copolymers[3,4,5,6,7], and intrinsically charged block copolymers containing both charged and neutral blocks[8,9,10,11,12,13]
Glimpses of the powerful role played by polymer-bound charges have been revealed by Park[24,25,26,27,28] and Balsara[29,30] and their coworkers, who demonstrated that the introduction of charged functional groups in either the PS or PEO blocks of poly(styrene)–b–poly(methylbutylene) (PS–PMB) and poly(styrene)–b–poly(ethylene oxide) (PS–PEO) diblock copolymers yields a variety of self-assembled morphologies, even from compositionally symmetric diblock systems
Summary
Charged block copolymers are of great interest due to their unique self-assembly and physicochemical properties. By manipulating the Coulombic cohesion of the system through the alteration of charge density and counterion properties, drastic shifts in the diblock-phase portraits were predicted, thereby anticipating potentially useful morphologies inaccessible with traditional neutral diblocks[20,21,22,23] Such theoretical predictions have not been experimentally elucidated yet, in part due to the difficulties in designing well-defined charged block copolymer model systems with precisely tuned charge fractions, and in part due to the broad parameter spaces to explore. Small-angle X-ray scattering (SAXS) experiments reveal the discovery of a superlattice state, located in phase space between the classical disordered and periodic lamellar morphologies as a function of the concentration of charge This finding points to fascinating and versatile approaches for manipulating the nanoscale structure and properties of soft materials
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