2018, Mendes, R.G., Wróbel, P.S., Bachmatiuk, A., Sun, J., Gemming, T., Liu, Z., Rümmeli, M.H.

The various forms of carbon nanostructures are providing extraordinary new opportunities that can revolutionize the way gas sensors, electrochemical sensors and biosensors are engineered. The great potential of carbon nanostructures as a sensing platform is exciting due to their unique electrical and chemical properties, highly scalable, biocompatible and particularly interesting due to the almost infinite possibility of functionalization with a wide variety of inorganic nanostructured materials and biomolecules. This opens a whole new pallet of specificity into sensors that can be extremely sensitive, durable and that can be incorporated into the ongoing new generation of wearable technology. Within this context, carbon-based nanostructures are amongst the most promising structures to be incorporated in a multi-functional platform for sensing. The present review discusses the various 1D, 2D and 3D carbon nanostructure forms incorporated into different sensor types as well as the novel functionalization approaches that allow such multi-functionality.

2019, Krause, Beate, Rzeczkowski, Piotr, Pötschke, Petra

Melt-mixed composites based on polypropylene (PP) with various carbon-based fillers were investigated with regard to their thermal conductivity and electrical resistivity. The composites were filled with up to three fillers by selecting combinations of graphite nanoplatelets (GNP), carbon fibers (CF), carbon nanotubes (CNT), carbon black (CB), and graphite (G) at a constant filler content of 7.5 vol%. The thermal conductivity of PP (0.26 W/(m·K)) improved most using graphite nanoplatelets, whereas electrical resistivity was the lowest when using multiwalled CNT. Synergistic effects could be observed for different filler combinations. The PP composite, which contains a mixture of GNP, CNT, and highly structured CB, simultaneously had high thermal conductivity (0.5 W/(m·K)) and the lowest electrical volume resistivity (4 Ohm·cm).

2019, Mičušík, Matej, Chatzimanolis, Christos, Tabačiarová, Jana, Kollár, Jozef, Kyritsis, Apostolos, Pissis, Polycarpos, Pionteck, Jürgen, Vegso, Karol, Siffalovic, Peter, Majkova, Eva, Omastová, Mária

Polymeric composites of the linear triblock copolymer poly(styrene-co-ethylene/butylene-co-styrene) grafted with maleic anhydride units (SEBS-MA) or MA modified by hydrophilic polyethylene glycol (PEG) and containing various amounts of multiwall carbon nanotubes (MWCNTs) as conducting filler—were prepared by solvent casting. The MWCNT surface was modified by a non-covalent approach with a pyrene-based surfactant to achieve a homogeneous dispersion of the conducting filler within the polymeric matrix. The dispersion of the unmodified and surfactant-modified MWCNTs within the elastomeric SEBS-MA and SEBS-MA-PEG matrices was characterized by studying the morphology by TEM and SAXS. Dynamical mechanical analysis was used to evaluate the interaction between the MWCNTs and copolymer matrix. The electrical conductivity of the prepared composites was measured by dielectric relaxation spectroscopy, and the percolation threshold was calculated. The prepared elastomeric composites were characterized and studied as humidity sensor. Our results demonstrated that at MWCNTs concentration slightly above the percolation threshold could result in large signal changes. In our system, good results were obtained for MWCNT loading of 2 wt% and an ~0.1 mm thin composite film. The thickness of the tested elastomeric composites and the source current appear to be very important factors that influence the sensing performance. © 2019 Mičušík, Chatzimanolis, Tabačiarová, Kollár, Kyritsis, Pissis, Pionteck, Vegso, Siffalovic, Majkova and Omastová.

2011, Mahanandia, P., Schneider, J.J., Engel, M., Stühn, B., Subramanyam, S.V., Nanda, K.K.

We report the synthesis of aligned arrays of millimeter long carbon nanotubes (CNTs), from benzene and ferrocene as the molecular precursor and catalyst respectively, by a one-step chemical vapor deposition technique. The length of the grown CNTs depends on the reaction temperature and increases from ~85 μm to ~1.4 mm when the synthesis temperature is raised from 650 to 1100°C, while the tube diameter is almost independent of the preparation temperature and is ~80 nm. The parallel arrangement of the CNTs, as well as their tube diameter can be verified spectroscopically by small angle X-ray scattering (SAXS) studies. Based on electron diffraction scattering (EDS) studies of the top and the base of the CNT films, a root growth process can be deduced.

2013, Botelho, E.C., Costa, M.L., Braga, C.I., Burkhart, T., Laukee, B.

Nanostructured polymer composites have opened up new perspectives for multi-functional materials. In particular, carbon nanotubes (CNTs) have the potential applications in order to improve mechanical and electrical performance in composites with aerospace application. This study focuses on the viscoelastic evaluation of phenolic resin reinforced carbon nanotubes, processed by using two techniques: aqueous-surfactant solution and three roll calender (TRC) process. According to our results a relative small amount of CNTs in a phenolic resin matrix is capable of enhancing the viscoelastic properties significantly and to modify the thermal stability. Also has been observed that when is used TRC process, the incorporation and distribution of CNT into phenolic resin is more effective when compared with aqueous solution dispersion process.

2019, Staudinger, Ulrike, Satapathy, Bhabani K., Jehnichen, Dieter

A nanostructured linear triblock copolymer based on styrene and butadiene with lamellar morphology is filled with multiwalled carbon nanotubes (MWCNTs) of up to 1 wt% by melt compounding. This study deals with the dispersability of the MWCNTs within the nanostructured matrix and its consequent impact on block copolymer (BCP) morphology, deformation behavior, and the electrical conductivity of composites. By adjusting the processing parameters during melt mixing, the dispersion of the MWCNTs within the BCP matrix are optimized. In this study, the morphology and glass transition temperatures (Tg) of the hard and soft phase are not significantly influenced by the incorporation of MWCNTs. However, processing-induced orientation effects of the BCP structure are reduced by the addition of MWCNT accompanied by a decrease in lamella size. The stress-strain behavior of the triblock copolymer/MWCNT composites indicate higher Young’s modulus and pronounced yield point while retaining high ductility (strain at break ~ 400%). At a MWCNT content of 1 wt%, the nanocomposites are electrically conductive, exhibiting a volume resistivity below 3 × 103 Ω·cm. Accordingly, the study offers approaches for the development of mechanically flexible functional materials while maintaining a remarkable structural property profile.

2014, Qi, H., Liu, J., Mäder, E.

Smart multi-walled carbon nanotube (MWCNT)-coated cellulose fibers with a unique sensing ability were manufactured by a simple dip coating process. The formation of electrically-conducting MWCNT networks on cellulose mono- and multi-filament fiber surfaces was confirmed by electrical resistance measurements and visualized by scanning electron microscopy. The interaction between MWCNT networks and cellulose fiber was investigated by Raman spectroscopy. The piezoresistivity of these fibers for strain sensing was investigated. The MWCNT-coated cellulose fibers exhibited a unique linear strain-dependent electrical resistance change up to 18% strain, with good reversibility and repeatability. In addition, the sensing behavior of these fibers to volatile molecules (including vapors of methanol, ethanol, acetone, chloroform and tetrahydrofuran) was investigated. The results revealed a rapid response, high sensitivity and good reproducibility for these chemical vapors. Besides, they showed good selectivity to different vapors. It is suggested that the intrinsic physical and chemical features of cellulose fiber, well-formed MWCNT networks and favorable MWCNT-cellulose interaction caused the unique and excellent sensing ability of the MWCNT-coated cellulose fibers, which have the potential to be used as smart materials.

2013, Giusca, C.E., Stolojan, V., Sloan, J., Börrnert, F., Shiozawa, H., Sader, K., Rümmeli, M.H., Büchner, B., Silva, S.R.P.

The demand for high-density memory in tandem with limitations imposed by the minimum feature size of current storage devices has created a need for new materials that can store information in smaller volumes than currently possible. Successfully employed in commercial optical data storage products, phase-change materials, that can reversibly and rapidly change from an amorphous phase to a crystalline phase when subject to heating or cooling have been identified for the development of the next generation electronic memories. There are limitations to the miniaturization of these devices due to current synthesis and theoretical considerations that place a lower limit of 2 nm on the minimum bit size, below which the material does not transform in the structural phase. We show here that by using carbon nanotubes of less than 2 nm diameter as templates phase-change nanowires confined to their smallest conceivable scale are obtained. Contrary to previous experimental evidence and theoretical expectations, the nanowires are found to crystallize at this scale and display amorphous-to-crystalline phase changes, fulfilling an important prerequisite of a memory element. We show evidence for the smallest phase-change material, extending thus the size limit to explore phase-change memory devices at extreme scales.

2018, Ghunaim, R., Damm, C., Wolf, D., Lubk, A., Büchner, B., Mertig, M., Hampel, S.

In the present work, different synthesis procedures have been demonstrated to fill carbon nanotubes (CNTs) with Fe1-xNix alloy nanoparticles (x = 0.33, 0.5). CNTs act as templates for the encapsulation of magnetic nanoparticles, and provide a protective shield against oxidation as well as prevent nanoparticles agglomeration. By variation of the reaction parameters, the purity of the samples, degree of filling, the composition and size of filling nanoparticles have been tailored and therefore the magnetic properties. The samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Bright-field (BF) TEM tomography, X-ray powder diffraction, superconducting quantum interference device (SQUID) and thermogravimetric analysis (TGA). The Fe1-x Nix-filled CNTs show a huge enhancement in the coercive fields compared to the corresponding bulk materials, which make them excellent candidates for several applications such as magnetic storage devices.

2018, Ghunaim, R., Scholz, M., Damm, C., Rellinghaus, B., Klingeler, R., Büchner, B., Mertig, M., Hampel, S.

In the present work, we demonstrate different synthesis procedures for filling carbon nanotubes (CNTs) with equimolar binary nanoparticles of the type Fe-Co. The CNTs act as templates for the encapsulation of magnetic nanoparticles and provide a protective shield against oxidation as well as prevent nanoparticle agglomeration. By variation of the reaction parameters, we were able to tailor the sample purity, degree of filling, the composition and size of the filling particles, and therefore, the magnetic properties. The samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), superconducting quantum interference device (SQUID) and thermogravimetric analysis (TGA). The Fe-Co-filled CNTs show significant enhancement in the coercive field as compared to the corresponding bulk material, which make them excellent candidates for several applications such as magnetic storage devices.