Competition between tubular network morphologies in diblock copolymer/homopolymer blends

Binary blends (BBs) of diblock copolymer (BCP)/homopolymer (HP) have been shown to be a more accessible way of attaining complex morphologies like Double Gyroid (Ia3d), Double Diamond (Pn3m), and Double Primitive (Im3m) over a wider compositional window. However, these phase assignments have involved either Transmission Electron Microscopy (TEM) projections (real space) that are hard to distinguish, or small angle x-ray scattering (SAXS) (reciprocal space) which are also equivocal. BBs of poly(styrene)-b-poly(isoprene) and (polystyrene)-b-poly(butadiene) (PS-b-PX) (X = PI/PB) with the respective low Tg PI or PB homopolymers (HP) were solution cast and annealed (125 C, 1 week). The HP component can occupy either the minority (channels) or majority (matrix) domains and act as wet or dry brush additives depending on the HP chain length relative to the respective block length. Real space Slice and View Scanning Electron Microscopy (SVSEM) tomography, reciprocal space 3D Fast Fourier Transform (FFT) and microfocus synchrotron SAXS are employed to unambiguously determine the tubular network structures. Experimental analysis is compared to newly computed SCFT calculations of BBs which aim to correlate thermodynamic shifts in network stability to sub-domain geometric features, including molecular packing of the BCP “host” morphology and spatial localization of the HP “guest” within it.