Lubrication of poly(vinyl alcohol) chain orientation by carbon nano-chips in composite tapes

3D Printing-Enabled Nanoparticle Alignment: A Review of Mechanisms and Applications

3D printing (additive manufacturing (AM)) has enormous potential for rapid tooling and mass production due to its design flexibility and significant reduction of the timeline from design to manufacturing. The current state-of-the-art in 3D printing focuses on material manufacturability and engineering applications. However, there still exists the bottleneck of low printing resolution and processing rates, especially when nanomaterials need tailorable orders at different scales. An interesting phenomenon is the preferential alignment of nanoparticles that enhance material properties. Therefore, this review emphasizes the landscape of nanoparticle alignment in the context of 3D printing. Herein, a brief overview of 3D printing is provided, followed by a comprehensive summary of the 3D printing-enabled nanoparticle alignment in well-established and in-house customized 3D printing mechanisms that can lead to selective deposition and preferential orientation of nanoparticles. Subsequently, it is listed that typical applications that utilized the properties of ordered nanoparticles (e.g., structural composites, heat conductors, chemo-resistive sensors, engineered surfaces, tissue scaffolds, and actuators based on structural and functional property improvement). This review's emphasis is on the particle alignment methodology and the performance of composites incorporating aligned nanoparticles. In the end, significant limitations of current 3D printing techniques are identified together with future perspectives.

In situ alignment of graphene nanoplatelets in poly(vinyl alcohol) nanocomposite fibers with controlled stepwise interfacial exfoliation

Hierarchically microstructured tri-axial poly(vinyl alcohol)/graphene nanoplatelet (PVA/GNP) composite fibers were fabricated using a dry-jet wet spinning technique. The composites with distinct PVA/GNPs/PVA phases led to highly oriented and evenly distributed graphene nanoplatelets (GNPs) as a result of molecular chain-assisted interfacial exfoliation. With a concentration of 3.3 wt% continuously aligned GNPs, the composite achieved a ∼73.5% increase in Young's modulus (∼38 GPa), as compared to the pure PVA fiber, and an electrical conductivity of ∼0.38 S m^-1, one of the best mechanical/electrical properties reported for polymer/GNP nanocomposite fibers. This study has broader impacts on textile engineering, wearable robotics, smart sensors, and optoelectronic devices.

Exfoliated Graphene Leads to Exceptional Mechanical Properties of Polymer Composite Films

Polymers with superior mechanical properties are desirable in many applications. In this work, polyethylene (PE) films reinforced with exfoliated thermally reduced graphene oxide (TrGO) fabricated using a roll-to-roll hot-drawing process are shown to have outstanding mechanical properties. The specific ultimate tensile strength and Young's modulus of PE/TrGO films increased monotonically with the drawing ratio and TrGO filler fraction, reaching up to 3.2 ± 0.5 and 109.3 ± 12.7 GPa, respectively, with a drawing ratio of 60× and a very low TrGO weight fraction of 1%. These values represent by far the highest reported to date for a polymer/graphene composite. Experimental characterizations indicate that as the polymer films are drawn, TrGO fillers are exfoliated, which is further confirmed by molecular dynamics (MD) simulations. Exfoliation increases the specific area of the TrGO fillers in contact with the PE matrix molecules. Molecular dynamics simulations show that the PE-TrGO interaction is stronger than the PE-PE intermolecular van der Waals interaction, which enhances load transfer from PE to TrGO and leverages the ultrahigh mechanical properties of TrGO.

Spray-Coated Halloysite-Epoxy Composites: A Means To Create Mechanically Robust, Vertically Aligned Nanotube Composites

Halloysite nanotube-filled epoxy composites were fabricated using spray-coating methods. The halloysite nanotubes (HNTs) were aligned by the hydrodynamic flow conditions at the spray nozzle, and the polymer viscosity helped to preserve this preferential orientation in the final coatings on the target substrates. Electron microscopy demonstrated a consistent trend of higher orientation degree in the nanocomposite coatings as viscosity increased. The nanoindentation mechanical performances of these coatings were studied using a Hysitron TriboIndenter device. Composites showed improvements up to ∼50% in modulus and ∼100% in hardness as compared to pure epoxy, and the largest improvements in mechanical performance correlated with higher alignment of HNTs along the plane-normal direction. Achieving this nanotube alignment using a simple spray-coating method suggests potential for large-scale production of multifunctional anisotropic nanocomposite coatings on a variety of rigid and deformable substrates.

Using Low Concentrations of Nano-Carbons to Induce Polymer Self-Reinforcement of Composites for High-Performance Applications

The current study focuses on the influence of low nano-carbon loading in polymer based composite fibers to modify matrix microstructure. With regards to the processing–structure–property relationship, post-spinning heat treatments (i.e., drawing, annealing without tension, and annealing with tension) was used to track microstructural development and associated mechanical property changes. Drawing and annealing procedures were found to influence the interphase volume fraction, fibril dimensions, sub-fibrillar lamellae, and sub-lamellae grain size for each sample. Annealing at 160 °C was found to have the largest impact on interphase percentage, fibril length, and grain packing density. These improvements corresponded to excellent mechanical properties for both control and composite fibers. Understanding the relationship between processing and property provides a novel perspective for producing high-performance composite materials from flexible polymers by only minimal amounts of carbon nano-fillers.

Structural Polymer-Based Carbon Nanotube Composite Fibers: Understanding the Processing-Structure-Performance Relationship

Among the many potential applications of carbon nanotubes (CNT), its usage to strengthen polymers has been paid considerable attention due to the exceptional stiffness, excellent strength, and the low density of CNT. This has provided numerous opportunities for the invention of new material systems for applications requiring high strength and high modulus. Precise control over processing factors, including preserving intact CNT structure, uniform dispersion of CNT within the polymer matrix, effective filler–matrix interfacial interactions, and alignment/orientation of polymer chains/CNT, contribute to the composite fibers’ superior properties. For this reason, fabrication methods play an important role in determining the composite fibers’ microstructure and ultimate mechanical behavior. The current state-of-the-art polymer/CNT high-performance composite fibers, especially in regards to processing–structure–performance, are reviewed in this contribution. Future needs for material by design approaches for processing these nano-composite systems are also discussed.

Tailoring polyacrylonitrile interfacial morphological structure by crystallization in the presence of single-wall carbon nanotubes

In order to improve stress transfer between polymer matrixes and nanofillers, controlling the structure development in the interphase region during composite processing is a necessity. For polyacrylonitrile (PAN)/single-wall carbon nanotubes (SWNT) composites, the formation of the PAN interphase in the presence of the SWNT as a function of processing conditions is studied. Under these conditions, three distinct interfacial coating morphologies of PAN are observed on SWNT. In the semidilute polymer concentration regime subjected to shearing, PAN extended-chain tubular coatings are formed on SWNT. Dilute PAN/SWNT quiescent solutions subjected to cooling yields hybrid periodic shish-kebab structures (first observation for PAN polymer), and dilute PAN/SWNT quiescent solutions subjected to rapid cooling results in the formation of an irregular PAN crystalline coating on the SWNT.