Fig. 1: Molecular structures of polymers, nanocomposite synthesis and, hybrid biaxial nematics.

a Molecular structures of PBDT and PBDI, mesophases (images from crossed polarized optical microscopy have been cropped into NMR tube shapes using Adobe Illustrator^TM), and chain secondary structures (schematic insets). PBDT has a rectilinear primary structure and adopts a prolate, rod-like secondary structure that spontaneously forms a uniaxial nematic phase in water above ≈1.9 wt.%. The PBDT rods are locally aligned along a nematic director, n_P; the solution appears bright between crossed polarizers. In contrast, the secondary structure of PBDI is a random coil globular shape with a primary structure that differs from that of PBDT only by the meta-linked isopthaloyl moiety; this substitution pattern introduces a bend into the PBDI secondary structure. PBDI solutions are isotropic and appear dark between crossed polarizers. b The water-based synthetic process to make PBDT + GO nanocomposite films. Stable PBDT + GO aqueous mixtures are obtained by simple mixing of the nematic components which on film casting and drying at 60 °C yields a nematic nanocomposite film (≈20 μm thick). c Phase stability of aqueous PBDT + GO mixtures. Nanocomposite precursor mixtures with a range of total solids concentrations (C_total = 1.7, 2.8, 4.9, and 7.1 wt.%) each with a constant GO/(PBDT + GO) mass fraction (F_GO = 0.0244). The 1.7 wt.% solution is isotropic, and the GO dispersion is metastable: Mild centrifugation (2 h at 600 RPM) results in the aggregation of flocculated GO in the lower isotropic phase (I_GO). Below C_total = 3.6 wt.%, the solutions are biphasic, e.g., centrifugation of the C_total = 2.8 wt.% mixture partitions into a PBDT-rich isotropic (I) upper phase coexisting with a birefringent PBDT + GO ^hN_b lower phase. Stable ^hN_b phases exist in nanocomposite precursor mixtures when C_total > 3.6 wt.%. d Aqueous PBDI + GO solutions, irrespective of concentration, are isotropic and mild centrifugation partitions it into an upper PBDI rich isotropic phase and a lower I_GO phase (e.g., C_total = 4.9 wt.%). The backgrounds in a, c, d have been changed from black to pink for visualization purposes.