Abstract
We designed and synthesized high χ-low N-maltoheptaose-(triazolium+/N(SO2CF3)2–)-polyisoprene-(triazolium+/N(SO2CF3)2–)-maltoheptaose ABA triblock elastomers featuring triazolium+/N(SO2CF3)2– (TFSI–) counteranion ionic interfaces separating their constituting polymeric sub-blocks. Spin-coated and solvent-vapor-annealed (SVA) MH1.2k-(T+/TFSI–)-PI4.3k-(T+/TFSI–)-MH1.2k thin films demonstrate interface-induced charge cohesion through ca. 1 nm “thick” ionic nanochannels which facilitate the self-assembly of a perpendicularly aligned lamellar structure. Atomic force microscopy (AFM) and (grazing-incidence) small-angle X-ray scattering ((GI)SAXS) characterizations of MH1.2k-(T+/TFSI–)-PI4.3k-(T+/TFSI–)-MH1.2k and pristine triBCP analogous thin films revealed sub-10 nm block copolymer (BCP) self-assembly and unidirectionally aligned nanostructures developed over several μm2 areas. Solvated TFSI– counterions enhance the oligosaccharide sub-block packing during SVA. The overall BCP phase behavior was mapped through SAXS characterizations comparing di- vs triblock polymeric architectures, a middle PI sub-block with two different molecular masses, and TFSI– or I– counteranion effects. This work highlights the benefits of inducing single-point electrostatic interactions within chemical structures of block copolymers to master the long-range self-assembly of prescribed morphologies.
Highlights
We designed and synthesized high χ-low N-maltohep(tliaSuoOms2+eC/-(NFt3(r)iS2aO−z)o2-CmliFua3ml)to2+−h/eN(pT(taFSoSOsIe−2C)AFcBo3A)u2nt−rte)ibr-laponocilkoynieslioaospntroicemnienert-se(rtffreaiacatezusorislnieugpmatrr+aia/tizNnog-their constituting polymeric sub-blocks
We report on the effect of electrostatic interactions at charge-modified block copolymer (BCP) interfaces to control the self-assembly of oligosaccharide-based high χ-low
We provide a direct vs reciprocal space quantification of sub-10 nm Lam domain spacing (d) in thin films with atomic force microscopy (AFM)
Summary
The AFM imaging of a grain boundary with merged facing line frontiers (Figure S16) supports the claims that dotted features (Figures 3 image 4 and S17) are nonequilibrium structures within a swollen BCP thin film This is compatible with dispersity-induced PI4.3k middleblock packing frustrations which affect the evolution of the surface morphology.[32]. To the best of our knowledge, this is the first report of a long-range unidirectional alignment for a BCP Lam nanostructure induced by electrostatic interactions within ionic nanochannels defined by T+/counteranion− junctions separating polymeric sub-blocks. TFSI− solubilization during SVA of the BCP thin film together with optimized film thickness enable long-range-ordered unidirectional perpendicular Lam formation, quantified for MH1.2k-(T+/TFSI−)-PI4.3k(T+/TFSI−)-MH1.2k thin film with both real-space (AFM) and reciprocal-space (GISAXS) analyses. Long-range nanostructure orientation is conveniently achieved without shearing or relying on graphoepitaxy, highlighting how electrostatic interactions facilitate BCP domain alignment through ionic
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