Merging versatile polymer chemistry with multifunctional nanoparticles: an overview of crosslinkable aromatic polyester matrix nanocomposites.

The current trend in the global advanced material market is expeditiously shifting towards more lightweight, multifunctional configurations, considering very recent developments in electrical aircraft, biomedical devices, and autonomous automobiles. Hence, the development of novel polymer nanocomposite materials is critical to advancing the current state-of-the-art of structural material technologies to address the pressing performance demands. Aiming at expanding the existing material design space, we have investigated crosslinkable aromatic polyester matrix nanocomposites. Aromatic polyesters, in the thermosetting form, are a prospective high-performance/high-temperature polymer technology, which is on a par with conventional epoxy-derivative resins and high-performance engineering thermoplastics in the range of their potential applications. The aromatic matrix-based thermosetting nanocomposites manifest greatly enhanced physical properties enabled by a chemistry-favored robust interfacial covalent coupling mechanism developed during the in situ polymerization reaction with various nanofiller particle configurations. Here, we provide a summary review of our recent efforts in developing this novel polymer nanocomposite material system. We highlight the chemical strategy, fabrication approach, and processing techniques developed to obtain various nanocomposite representations for structural, electrical, optical, biomedical, and tribological applications. The unique characteristic features emerging in the nanocomposite morphologies, along with their physicochemical effects on the multifunctional macroscale properties, are demonstrated. This unique matrix configuration introduces superior performance elements to polymer nanocomposite applications towards designing advanced composite materials.

Aromatic thermosetting copolyester bionanocomposites as reconfigurable bone substitute materials: Interfacial interactions between reinforcement particles and polymer network.

Development of porous materials consisting of polymer host matrix enriched with bioactive ceramic particles that can initiate the reproduction of cellular organisms while maintaining in vivo mechanical reliability is a long-standing challenge for synthetic bone substitutes. We present hydroxyapatite (HA) reinforced aromatic thermosetting copolyester (ATSP) matrix bionanocomposite as a potential reconfigurable bone replacement material. The nanocomposite is fabricated by solid-state mixing a matching set of precursor oligomers with biocompatible pristine HA particles. During endothermic condensation polymerization reaction, the constituent oligomers form a mechanochemically robust crosslinked aromatic backbone while incorporating the HAs into a self-generated cellular structure. The morphological analysis demonstrates near-homogenous distributions of the pristine HAs within the matrix. The HAs behave as a crack-arrester which promotes a more deformation-tolerant formation with relatively enhanced material toughness. Chain relaxation dynamics of the nanocomposite matrix during glass transition is modified via HA-induced segmental immobilization. Chemical characterization of the polymer backbone composition reveals the presence of a hydrogen-advanced covalent interfacial coupling mechanism between the HAs and ATSP matrix. This report lays the groundwork for further studies on aromatic thermosetting copolyester matrix bionanocomposites which may find applications in various artificial bone needs.

Nanofiller-conjugated percolating conductive network modified polymerization reaction characteristics of aromatic thermosetting copolyester resin.

Deliberately controlled interfacial interactions between incorporated nanofiller particles and host polymer backbone chains constitute a critical element in the realm of polymer nanocomposites with tailorable multifunctional properties. We demonstrate the physicochemical effects induced by graphene nanoplatelets (GNP) of different sizes on the condensation polymerization reaction of aromatic thermosetting copolyester (ATSP) through the formation of electrically conductive percolating networks as enabled by interfacial interactions. Carboxylic acid and acetoxy-capped precursor oligomers of ATSP are solid-state mixed with chemically pristine GNP particles at various loading levels. Upon in situ endothermic condensation polymerization reaction, crosslinked backbone of the ATSP foam matrix is formed while the carbonaceous nanofillers are incorporated into the polymer network via covalent conjugation with functional end-groups of the oligomers. The controlled GNP size promotes different electrical percolation thresholds and ultimate electrical conductivities. Microstructural analysis demonstrates GNP distributions in the matrix as well as morphological modifications induced by the formation of conductive percolating GNP networks. Cure characteristics reveal the thermochemical changes prompted in the polymerization processes for GNP content above the requirement for percolation formation. Chemical spectroscopy of the ATSP nanocomposite morphology exhibits the formation of a robust interfacial coupling mechanism between the GNPs and ATSP backbone. The findings here may guide the developmental efforts of nanocomposites through better identifying roles of the morphology and content of nanofillers in polymerization processes.

Multifunctional atomic force microscope cantilevers with Lorentz force actuation and self-heating capability.

This paper reports the development of microcantilevers capable of self-heating and Lorentz-force actuation, and demonstrates applications to thermal topography imaging. Electrical current passing through a U-shaped cantilever in the presence of a magnetic field induces a Lorentz force on the cantilever free end, resulting in cantilever actuation. This same current flowing through a resistive heater induces a controllable temperature increase. We present cantilevers designed for large actuation forces for a given cantilever temperature increase. We analyze the designs of two new cantilevers, along with a legacy cantilever design. The cantilevers are designed to have a spring constant of about 1.5 N m(-1), a resonant frequency near 100 kHz, and self-heating capability with temperature controllable over the range 25-600 °C. Compared to previous reports on self-heating cantilevers, the Lorentz-thermal cantilevers generate up to seven times as much Lorentz force and two times as much oscillation amplitude. When used for thermal topography imaging, the Lorentz-thermal cantilevers can measure topography with a vertical resolution of 0.2 nm.