2, ATSP Innovations, Urbana, Illinois, United States
3, Tallinn University of Technology, Tallinn, , Estonia
4, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
5, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
The realization of a robust interfacial attachment mechanism between nanofillers and host polymer matrix holds great promise to enhance overall macroscale properties of nanocomposites. With this regard, the formation of periodically functionalized and crystalline texture shish-kebab architectures on matrix-embedded nanostrands through utilizing intrinsic characteristics of semicrystalline polymer systems represents a facile interfacial coupling scheme. In particular, successful protocols for the development of periodically assembled shish-kebab structures have been demonstrated on CNTs employing numerous semicrystalline polymer systems. Yet, the functionalized nano-hybrid shish-kebab configurations are essentially established via intrinsically semicrystalline thermoplastics which genuinely constitute inferior physical properties for high-performance demanding applications. Aromatic thermosetting copolyester (ATSP), introduced in the late 1990s, utilizes low cost, easily processable and highly crosslinkable oligomers to develop a high-performance polymer system. The crosslinked morphology of ATSP formed by an aromatic polyester backbone interconnected via covalent oxygen bonds enables strong physical properties and outstanding chemical inertness. Here, we report on in situ epitaxial step-growth polymerization driven interfacial functionalization of ATSP with multi-layered graphene wrapped alumina nanofiber (ANFC) surface. Unidirectionally oriented ANFC bundles are dip-coated with both dilute and concentrated ATSP oligomer solutions. During a thermal condensation polymerization, ATSP dip-coated fiber strands develop a nano-hybrid shish-kebab structure with periodically assembled and off-surface grown micron-scale lamella ATSP domains. The nano-hybrid ATSP-ANFC system is composed of the ANFC strand as “shish” and the ATSP lamellae as “kebab” in the nanocomposite structure, which also clearly highlights the epitaxial growth induced localized lamellae formation. The condensation polymerized thermoset nature of the lamellae also presents a unique synthetic route as compared to previously reported shish-kebab structures. We propose a mechanism combining the Plateau-Rayleigh instability, the Marangoni effect and the epitaxial growth phenomena to elucidate controlling parameters in the process. X-ray Diffraction measurements clearly demonstrate the formation of mesomorphic lamella phase not present within either the neat ATSP or pristine fiber samples. Results of solid-state Nuclear Magnetic Resonance and Thermogravimetric Analysis reveal the development of an interfacial coupling between the graphene-coated ceramic nanofibers and the ATSP matrix. This study lays the groundwork to initiate further analyses of the ATSP with various other nanofiller reinforcements on the in situ surface functionalization.