The electrical properties of polymer nanocomposites containing a small amount of carbon
nanotube (CNT) are remarkably superior to those of conventional electronic composites. Based on three-dimensional (3D) statistical percolation and 3D resistor network modeling, the electrical properties of CNT nanocomposites, at and after percolation, were successfully predicted in this work. The numerical analysis was also extended to investigate the effects of the aspect ratio, the electrical conductivity, the aggregation and the shape of CNTs on the electrical properties of the nanocomposites. A simple empirical model was also established based on present numerical simulations to predict the electrical conductivity in several electronic composites with various fillers. This investigation further highlighted the importance
of theoretical and numerical analyses in the exploration of basic physical phenomena, such as percolation and conductivity in novel nanocomposites.

The electrical properties of polymer nanocomposites with carbon nanotube fillers

We present electrical conductivity measurements and modeling aspects of carbon nanotube (CNT)/polymer composites enabled via fused filament fabrication (FFF) additive manufacturing (AM). CNT/polylactic acid (PLA) and CNT/high density polyethylene (HDPE) filament feedstocks were synthesized through melt blending with controlled CNT loading to realize 3D printed polymer nanocomposites. Electrical conductivity of 3D printed CNT/PLA and CNT/HDPE composites was measured for various CNT loadings. Low percolation thresholds were obtained from measured data as 0.23 vol. % and 0.18 vol. % of CNTs for CNT/PLA and CNT/HDPE nanocomposites, respectively. Moreover, a micromechanics-based two-parameter agglomeration model was developed to predict the electrical conductivity of CNT/polymer composites. We further show that the two agglomeration parameters can also be used to describe segregated structures, wherein nanofillers are constrained to certain locations within the matrix. To the best of our knowledge, this is the first ever electrical conductivity model to account for segregation of CNTs in the matrix. A good agreement between measured conductivity and predictions demonstrates the adequacy of the proposed model. We further evince the robustness of the model by accurately capturing the conductivity measurements reported in the literature for both elastomeric and thermoplastic nanocomposites. The findings of the study would provide guidelines for the design of electro-conductive polymer nanocomposites.

Electrical conductivity of CNT/polymer composites: 3D printing, measurements and modeling

The study is focused on multifunctional performance of carbon nanotubes (CNT) and Graphene nanoplatelets (GNP) reinforced PEEK composites enabled via fused filament fabrication (FFF) additive manufacturing (AM) utilizing in-house nanoengineered filaments. Thermo-physical, mechanical and wear characteristics of electro-conductive PEEK nanocomposites are reported. The coefficient of thermal expansion (CTE) is found to decrease by 26% and 18% with the incorporation of 5 wt% GNP and 3 wt% CNT into PEEK polymer, respectively. The decrease in CTE provides better dimensional stability to resulting nanocomposite structures. Due to uniform dispersion of CNT and GNP in the PEEK matrix, the crystallization temperature and degree of crystallinity are both increased. The 3D printed PEEK nanocomposites reveal interfacial voids between the beads and intra-bead pores and thus exhibit lower density compared to that of the 3D printed neat PEEK. Young's and storage moduli are found to increase by 20% and 66% for 3 wt% CNT loading and by 23% and 72% for 5 wt% GNP loading respectively. However, the PEEK nanocomposites exhibit similar tensile strength to that of neat PEEK. The coefficient of friction obtained from fretting wear tests is found to decrease by 67% and 56% for 1 wt% CNT and 3 wt% GNP loaded PEEK nanocomposites, respectively and the decrease is attributed to reduced hardness and increased porosity. Multifunctional performance of carbon nanostructures reinforced AM-enabled PEEK composites demonstrated here makes them suitable for a range of applications such as orthopedics, oil and gas, automotive, electronics and space.

Multifunctional performance of carbon nanotubes and graphene nanoplatelets reinforced PEEK composites enabled via FFF additive manufacturing

Anti-bacterial scaffolds made of copper, bronze and silver particles filled PLA nanocomposites were realized via fused filament fabrication (FFF), additive manufacturing. The thermal, mechanical and biological characteristics including bioactivity and bactericidal properties of the scaffolds were evaluated. The incorporation of bronze particles into the neat PLA increases the elastic modulus up to 10% and 27% for samples printed in 0° and 90° configurations respectively. The stiffness increases, up to 103% for silver filled PLA nanocomposite scaffolds. The surface of scaffolds was treated with acetic acid to create a thin porous network. Significant increase (~20-25%) in the anti-bacterial properties and bioactivity (~18-100%) is attributed to the synergetic effect of reinforcement of metallic/metallic alloy particles and acid treatment. The results indicate that PLA nanocomposites could be a potential candidate for bone scaffold applications.

Microarchitected 3D printed polylactic acid (PLA) nanocomposite scaffolds for biomedical applications.

The characteristics of an electrorheological (ER) fluid, as a class of smart soft matter, can be actively and accurately tuned between a liquid- and a solid-like phase by the application of an electric field. ER materials used in ER fluids are electrically polarizable particles, which are attracting considerable attention in addition to further research. This perspective reports the latest ER materials along with their rheological understanding and provides a forward-looking summary of the potential future applications of ER technology.

Recent development of electro-responsive smart electrorheological fluids

Here, we report the electrical, mechanical and thermal properties of ultrahigh-molecular-weight polyethylene (UHMWPE) nanocomposites reinforced with 0.1 wt% to 10 wt% of graphene nanoplatelets (GNP). The electrical conductivity of GNP/UHMWPE nanocomposites shows percolation threshold at 3.0 wt% of GNP. A significant increase in electrical conductivity from 10−15 S cm−1 for neat UHMWPE to 10−5 S cm−1 at 3.0 wt% GNP loading of GNP/UHMWPE nanocomposite (i.e. 10 orders of magnitude higher) is due to the formation of an almost three-dimensional conductive network. The highest value of electrical conductivity (1.09 S cm−1) is observed at 10.0 wt% of GNP loading. The elastic modulus and yield strength increase by 30% and 21%, for the addition of 0.5 wt% and 1.0 wt% of GNP, respectively, while fracture toughness and the ultimate tensile strength decrease significantly above 0.5 wt% GNP loading. This study demonstrates the fabrication of GNP/UHMWPE bio-nanocomposites, which exhibit electrical properties useful for smart biomedical implants.

Electrical, mechanical and thermal properties of graphene nanoplatelets reinforced UHMWPE nanocomposites

Strain and damage-sensing performance of biocompatible smart CNT/UHMWPE nanocomposites

Ultra-high molecular weight polyethylene (UHMWPE)-based conductive nanocomposites with reduced percolation and tunable piezoresistive behavior were prepared via solution mixing followed by compression molding using carbon nanotubes (CNT) and graphene nanoplatelets (GNP). The effect of varying wt% of GNP with fixed CNT content (0.1 wt%) on the mechanical, electrical, thermal and piezoresistive properties of UHMWPE nanocomposites was evaluated. The combination of CNT and GNP enhanced the dispersion in UHMWPE matrix and lowered the probability of CNT aggregation as GNP acted as a spacer to separate the entanglement of CNT with each other. This has allowed the formation of an effective conductive path between GNP and CNT in UHMWPE matrix. The thermal conductivity, degree of crystallinity and degradation temperature of the nanocomposites increased with increasing GNP content. The elastic modulus and yield strength of the nanocomposites were improved by 37% and 33%, respectively, for 0.1/0.3 wt% of CNT/GNP compared to neat UHMWPE. The electrical conductivity was measured using four-probe method, and the lowest electrical percolation threshold was achieved at 0.1/0.1 wt% of CNT/GNP forming a nearly two-dimensional conductive network (critical value, t = 1.20). Such improvements in mechanical and electrical properties are attributed to the synergistic effect of the two-dimensional GNP and one-dimensional CNT which limits aggregation of CNTs enabling a more efficient conductive network at low wt% of fillers. These hybrid nanocomposites exhibited strong piezoresistive response with sensitivity factor of 6.2, 15.93 and 557.44 in the linear elastic, inelastic I and inelastic II regimes, respectively, for 0.1/0.5 wt% of CNT/GNP. This study demonstrates the fabrication method and the self-sensing performance of CNT/GNP/UHMWPE nanocomposites with improved properties useful for orthopedic implants.

M. Choosri

Papers

Electrical, mechanical and thermal properties of graphene nanoplatelets reinforced UHMWPE nanocomposites

Strain and damage-sensing performance of biocompatible smart CNT/UHMWPE nanocomposites

Self-sensing and mechanical performance of CNT/GNP/UHMWPE biocompatible nanocomposites