We report on the morphology and mechanical properties of nanocomposite films derived from aqueous, hybrid liquid crystalline mixtures of rodlike aggregates of a sulfonated, all-aromatic polyamide, poly(2,2′-disulfonyl-4,4′-benzidine terephthalamide) (PBDT), and graphene oxide (GO) platelets. An isothermal step at 200 °C facilitates in situ partial thermal reduction of GO to reduced GO (rGO) in nanocomposite films. X-ray scattering studies reveal that PBDT-rGO nanocomposites exhibit both higher in-plane alignment of PBDT (the order parameter increases from 0.79 to 0.9 at 1.8 vol % rGO) and alignment along the casting direction (from 0.1 to 0.6 at 1.8 vol % rGO). From dynamic mechanical thermal analysis, the interaction between PBDT and rGO causes the β-relaxation activation energy for PBDT to increase with rGO concentration. Modulus mapping of nanocomposites using atomic force microscopy demonstrates enhanced local stiffness, indicating reinforcement. From stress-strain analysis, the average Young's modulus increases from 16 to 37 GPa at 1.8 vol % rGO and the average tensile strength increases from 210 to 640 MPa. Despite polymer alignment along the casting direction, an average transverse tensile strength of 230 MPa is obtained.

Thermoplastic polyaryletherketones (PAEKs) exhibit excellent mechanical properties and fluid stability, but their glass transition temperatures (Tg) are low and their all-aromatic nature makes processing challenging. We will present a synthetic route toward phenylethynyl-functionalized hyperbranched PAEKs (hbPAEKs) (Tg = 151 °C) that can be cross-linked to form flexible films with high Tg's (187-237 °C) and good mechanical properties (E′ = 4 GPa, σ = 44 MPa, and ϵ = 1.76%). After cross-linking, the films are amorphous, easy to handle, and insoluble. We will report on the melt rheology of the hbPAEK precursors, with and without reactive phenylethynyl-reactive functionalities, and the thermomechanical characteristics of thin cross-linked films using dynamic mechanical thermal analysis, differential scanning calorimetry, and tensile testing. We believe that our findings can be extended to other all-aromatic structural and functional polymer architectures that are otherwise impossible to process.

We report irreversible, shear-activated gelation in liquid crystalline solutions of a rigid polyelectrolyte that forms rodlike assemblies (rods) in salt-free solution. At rest, the liquid crystalline solutions are kinetically stable against gelation and exhibit low viscosities. Under steady shear at, or above, a critical shear rate, a physically cross-linked, nematic gel network forms due to linear growth and branching of the rods. Above a critical shear rate, the time scale of gelation can be tuned from hours to nearly instantaneously by varying the shear rate and solution concentration. The shear-activated gels are distinct in their structure and rheological properties from thermoreversible gels. At a fixed concentration, the induction time prior to gelation decreases exponentially with the shear rate. This result indicates that shear-activated thermalization of the electrostatically stabilized rods overcomes the energy barrier for rod-rod contact, enabling rod fusion and subsequent irreversible network formation.