Shear alignment of a poly(styrene-butadiene-styrene) triblock copolymer/MWCNT nanocomposite

Electrical Conductivity and In Situ SAXS Probing of Block Copolymer Nanocomposites Under Mechanical Stretching

Elastomers based on block copolymers can self-organize into ordered nanoscale structures, making them attractive for use as flexible conductive nanocomposites. Understanding how ordered structures impact electrical properties is essential for practical applications. This study investigated the morphological evolution of flexible conductive elastomers based on polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (SEBS) block copolymers with aligned single- or multi-wall carbon nanotubes (SWCNTs or MWCNTs) and their electrical conductivity under large deformations. Oriented nanocomposites were obtained through injection molding and characterized using two different setups: tensile testing monitored by in situ small-angle X-ray scattering (SAXS) and tensile testing with simultaneous electrical conductivity measurements. Our findings demonstrate that structural orientation significantly influences electrical conductivity, with higher conductivity in the longitudinal direction due to the preferred orientation of carbon nanotubes. Tensile testing demonstrated that carbon nanotubes accelerate the process of realignment of the ordered structure. As a consequence, higher deformations reduced the conductivity of samples with longitudinal alignment due to the disruption of percolation contacts between nanotubes, while in samples with a transverse alignment the process promoted the formation of a new conductive network, increasing electrical conductivity.

Microphase separation assisted reduction in the percolation threshold of MWCNT/block polymer composites

Block copolymers continue to attract a great deal of interest since they allow the formation of microphase-separated domains, useful for nanopatterning/templating. Herein, we present the drastic effect of microphase separation of a diblock copolymer on the electrical properties of polymer nanocomposites. Microphase-separated poly(styrene-b-2-ethylhexyl acrylate) (P(St-b-EHA)) block copolymers having different block lengths were synthesized and utilized as templates for multi-walled carbon nanotubes (MWCNTs). The percolation threshold of the films decreased from 0.46 to 0.19 vol% with decreasing styrene phase fraction. More importantly, we observed a non-linear and unique reduction in percolation threshold with transforming the phase into lamellar structures.

Medical-Grade Polyamide 12 Nanocomposite Materials for Enhanced Mechanical and Antibacterial Performance in 3D Printing Applications

During the COVID-19 pandemic, wide use of 3D printing technologies has been enabled. Fused filament fabrication (FFF) is the most widely used technique in 3D printing communities worldwide for the fabrication of medical components such as face shields and respiratory valves. In the current study, the potential of Polyamide 12 (PA12) silver-doped antibacterial nanopowder (AgDANP) nanocomposites is evaluated for everyday FFF usage. Filling loadings of 1.0-2.0-3.0 and 4.0 wt.% were selected for nanocomposite preparation. Mechanical performance analysis was conducted on the basis of tensile, flexural, impact, and Vickers microhardness measurements in FFF 3D-printed specimens. Scanning Electron Microscopy (SEM) images were used for morphology and processing evaluation, as well as thermal performance measurements, conducted by Thermogravimetric Analysis (TGA) tests. Finally, the antibacterial performance was tested using the agar-well diffusion screening method, and the shape effect of the specimens was also investigated. The addition of 2.0 wt.% AgDANPs resulted in an enhancement of approximately 27% for both tensile and flexural stresses, while the antibacterial performance was sufficiently high among the nanocomposites tested. The shape effect exhibited the potential for antibacterial performance at low filling ratios, while the effect was diminished with increasing filler of AgDANPs.

Mechanical Performance of Fused Filament Fabricated and 3D-Printed Polycarbonate Polymer and Polycarbonate/Cellulose Nanofiber Nanocomposites

In this study, nanocomposites were fabricated with polycarbonate (PC) as the matrix material. Cellulose Nanofiber (CNF) at low filler loadings (0.5 wt.% and 1.0 wt.%) was used as the filler. Samples were produced using melt mixing extrusion with the Fused Filament Fabrication (FFF) process. The optimum 3D-printing parameters were experimentally determined and the required specimens for each tested material were manufactured using FFF 3D printing. Tests conducted for mechanical performance were tensile, flexural, impact, and Dynamic Mechanical Analysis (DMA) tests, while images of the side and the fracture area of the specimens were acquired using Scanning Electron Microscopy (SEM), aiming to determine the morphology of the specimens and the fracture mechanism. It was concluded that the filler’s ratio addition of 0.5 wt.% created the optimum performance when compared to pure PC and PC CNF 1.0 wt.% nanocomposite material.

Design, Development and Evaluation of Thermal Properties of Polysulphone-CNT/GNP Nanocomposites

Polysulphone (PSU) composites with carbon nanotubes (PSU-CNT) and graphene nanoplatelets (PSU-GNP) were developed through the solution casting process, using various weight load percentages of 1, 3, 5, and 10 wt% of CNT and GNP nanofillers. The microstructural and thermal properties of the PSU-based composites were compared. The microstructural characterisation of both composites (PSU-CNTs and PSU-GNPs) showed a strong matrix–filler interfacial interaction and uniform dispersion of CNTs and GNPs in the PSU matrix. The analysis demonstrated that both the thermal conductivity and effusivity improved with the increase in the weight percentage (wt%) of CNTs and GNPs because of the percolation effect. The polysulphone-based composite containing 10 wt% CNTs showed a remarkably high thermal conductivity value of 1.13 (W/m·K), which is 163% times higher than pure PSU. While the glass transition temperature (Tg) was shifted to a higher temperature, the thermal expansion was reduced in all the PSU-CNT and PSU-GNP composites. Interestingly, the CNTs allowed homogeneous distribution and a reasonably good interfacial network of interaction with the PSU matrix, leading to better microstructural characteristics and thermal properties than those of the PSU-GNP composites. The findings highlight the importance of controlling the nature, distribution, and content of fillers within the polymeric matrix.

Three-Dimensional (3D) Conductive Network of CNT-Modified Short Jute Fiber-Reinforced Natural Rubber: Hierarchical CNT-Enabled Thermoelectric and Electrically Conductive Composite Interfaces

Jute fibers (JFs) coated with multiwall carbon nanotubes (MWCNTs) have been introduced in a natural rubber (NR) matrix creating a three-dimensional (3D) electrically conductive percolated network. The JF-CNT endowed electrical conductivity and thermoelectric properties to the final composites. CNT networks fully covered the fiber surfaces as shown by the corresponding scanning electron microscopy (SEM) analysis. NR/JF-CNT composites, at 10, 20 and 30 phr (parts per hundred gram of rubber) have been manufactured using a two-roll mixing process. The highest value of electrical conductivity (σ) was 81 S/m for the 30 phr composite. Thermoelectric measurements revealed slight differences in the Seebeck coefficient (S), while the highest power factor (PF) was 1.80 × 10⁻² μW/m K⁻² for the 30 phr loading. The micromechanical properties and electrical response of the composite’s conductive interface have been studied in peak force tapping quantitative nanomechanical (PFT QNM) and conductive atomic force microscopy (c-AFM) mode. The JF-CNT create an electrically percolated network at all fiber loadings endowing electrical and thermoelectric properties to the NR matrix, considered thus as promising thermoelectric stretchable materials.

A flexible carbon nanotube-modified poly(styrene-butadiene)-based dopamine sensor

In this work, a multi-walled carbon nanotube-modified flexible poly(styrene-butadiene) fiber membrane material was prepared for the sensitive and selective electrochemical detection of dopamine (DA) in human serum and DA injection. The flexible fiber membrane prepared by electrospinning technology is expected to realize its application in wearable devices. The obtained conductive film-based electrochemical sensor can effectively minimize interference caused by ascorbic acid and uric acid. Under the optimized experimental conditions of differential pulse voltammetry, DA gives a linear response in the range of 1-650 μM (R² = 0.996). The detection limit of DA (signal-to noise ratio = 3) was determined to be 0.062 μM.

The Role of Synergies of MWCNTs and Carbon Black in the Enhancement of the Electrical and Mechanical Response of Modified Epoxy Resins

Nano-reinforced composites are widely studied by the scientific community. The main factors affecting the final nanocomposite performance are the filler type and content, as well as the duration of the dispersion. In this work, we report the effects of Multi-Walled Carbon Nano Tubes (MWCNTs) and milled Carbon Black (CB) dispersion in epoxy resin on the electrical and mechanical properties of the resulting composites. Impedance Spectroscopy (IS) was utilized to assess the dielectric properties of the specimens. The mechanical properties were evaluated by fracture toughness tests, while Scanning Electron Microscopy (SEM) was performed to study the influence of the reinforcement on the failure mechanisms acting on the fracture surfaces of the specimens. IS results for epoxy/CNT systems revealed the creation of a 3D conductive network for concentrations above 0.3 wt. %, while CB did not result in the formation of such a network for filler contents up to 2 wt. %. However, the synergistic effect of CNTs/CB was successfully manifested by both the optimal electrical properties and the 81% enhanced fracture toughness in comparison to the neat resin. Fractography confirmed the aforementioned results and revealed the fracture mechanisms of all systems, such as crack pinning and deflection, and particle pull-out phenomena.

An Experimental Study on the Shear Behaviors of Polymer-Sand Composite Materials after Immersion

Sand mixed with geotextile/fiber/cement/lime or non-traditional chemical additives to form composite materials is recognized as an effective method for improving the sand properties. In this work, the variation in properties of composite materials after immersion is reported which has rarely appeared in the literature. The focus of this study is to evaluate the shear behaviors of polymer-sand composite material after immersion with direct shear tests. Several factors which may influence the shear behaviors after immersion are analyzed. The results demonstrate that this composite material still has good shear behaviors after immersion when compared to the purely sand material. The shear behaviors are improved with an increment in the curing time, polymer content and sand dry density while there is a decrease in the shear behaviors with increasing immersion time. The interaction between sand particles and the polymer are analyzed with Scanning Electron Microscope (SEM). The polymer membranes are formed by polymer enwrapping and connected sand particles to build an elastic and viscous structure in the sand that increases the interlocking forces between sand particles and decreases the void ratio of this material. The membranes are softened in water resulting in a decrease in the shear strength. Moreover, other factors affect the shear behaviors by improving the completeness and stability of this structure.

Construction of a Different Polymer Chain Structure to Study π-π Interaction between Polymer and Reduced Graphene Oxide

In this work, a different polymer chain structure was synthesized to study π-π interactions between polymer and reduced graphene oxide (RGO). Polymers with different chain structures were obtained from free radical copolymerization of styrene with 4-cyanostyrene (containing substituted phenyl rings) and 2-vinylnaphthalene (containing naphthalene rings). In this work, the polystyrene, poly(styrene-co-4-cyanostyrene) and poly(styrene-co-2-vinylnaphthalene) were named as PS, PSCN and PSNP, respectively. RGO was prepared through modified Hummers' method and further thermal reduction, and nanocomposites were prepared by solution blending. Thus, different π-π interactions were formed between polymers and RGO. Raman and thermal gravimetric analysis (TGA) were used to characterize the interfacial interaction, showing that the trend of the interfacial interaction should be in the order of RGO/PSCN, RGO/PS, and RGO/PSNP. The differential scanning calorimetry (DSC) measurement showed that, compared with polymer matrix, the glass transition temperature (Tg) of RGO/PS, RGO/PSCN and RGO/PSNP nanocomposites with the addition of 4.0 wt% RGO are increased by 14.3 °C, 25.2 °C and 4.4 °C, respectively. Compared with π-π interaction only formed through aromatic rings, substituent groups changed the densities of electron clouds on the phenyl rings. This change resulted in the formation of donor-acceptor interaction and reinforcement of the π-π interaction at the interface, which leads to increased value of Tg. This comparative study can be useful for selecting appropriate interaction groups, as well as suitable monomers, to prepare high performance nanocomposites.