Paintable Carbon Nanotube Coating-Based Textronics for Sustained Holter-Type Electrocardiography.

A growing population suffering from or at high risk of developing cardiovascular diseases can benefit from rapid, precise, and readily available diagnostics. Textronics is an interdisciplinary approach for designing and manufacturing high-performance flexible electronics integrated with textiles for various applications, with electrocardiography (ECG) being the most convenient and most frequently used diagnostic technique for textronic solutions. The key challenges that still exist for textronics include expedient manufacturing, adaptation to human subjects, sustained operational stability for Holter-type data acquisition, reproducibility, and compatibility with existing solutions. The present study demonstrates conveniently paintable ECG electroconductive coatings on T-shirts woven from polyester or 70% polyamide and 30% polyester. The up to 600-µm-thick coatings encompass working electrodes of low resistivity 60 Ω sq-1 sheathed in the insulated pathways-conjugable with a wireless, multichannel ECG recorder. Long (800 µm) multiwalled carbon nanotubes, with scalable reproducibility and purity (18 g per round of synthesis), constituted the electroactive components and were embedded into a commercially available screen-printing acrylic base. The resulting paint had a viscosity of 0.75 Pa·s at 56 s-1 and 25 °C and was conveniently applied using a paintbrush, making this technique accessible to manufacturers. The amplified and nondigitally processed ECG signals were recorded under dry-skin conditions using a certified ECG recorder. The system enabled the collection of ECG signals from two channels, allowing the acquisition of cardiac electrical activity on six ECG leads with quality at par with medical diagnostics. Importantly, the Holter-type ECG allowed ambulatory recording for >24 h under various activities (sitting, sleeping, walking, and running) in three male participants. The ECG signal was stable for >5 cycles of washing, a level of stability not reported yet previously. The developed ECG-textronic application possesses acceptable and reproducible characteristics, making this technology a suitable candidate for further testing in clinical trials.

High-Performance Ionanofluids from Subzipped Carbon Nanotube Networks.

Investments in the transfer and storage of thermal energy along with renewable energy sources strengthen health and economic infrastructure. These factors intensify energy diversification and the more rapid post-COVID recovery of economies. Ionanofluids (INFs) composed of long multiwalled carbon nanotubes (MWCNTs) rich in sp2-hybridized atoms and ionic liquids (ILs) display excellent thermal conductivity enhancement with respect to the pure IL, high thermal stability, and attractive rheology. However, the influence of the morphology, physicochemistry of nanoparticles and the IL-nanostructure interactions on the mechanism of heat transfer and rheological properties of INFs remain unidentified. Here, we show that intertube nanolayer coalescence, supported by 1D geometry assembly, leads to the subzipping of MWCNT bundles and formation of thermal bridges toward 3D networks in the whole INF volume. We identified stable networks of straight and bent MWCNTs separated by a layer of ions at the junctions. We found that the interactions between the ultrasonication-induced breaking nanotubes and the cations were covalent in nature. Furthermore, we found that the ionic layer imposed by close MWCNT surfaces favored enrichment of the cis conformer of the bis(trifluoromethylsulfonyl)imide anion. Our results demonstrate how the molecular perfection of the MWCNT structure with its supramolecular arrangement affects the extraordinary thermal conductivity enhancement of INFs. Thus, we gave the realistic description of the interactions at the IL-CNT interface with its (super)structure and chemistry as well as the molecular structure of the continuous phase. We anticipate our results to be a starting point for more complex studies on the supramolecular zipping mechanism. For example, ionically functionalized MWCNTs toward polyionic systems─of projected and controlled nanolayers─could enable the design of even more efficient heat-transfer fluids and miniaturization of flexible electronics.

Biomimetically Inspired Highly Homogeneous Hydrophilization of Graphene with Poly(l-DOPA): Toward Electroconductive Coatings from Water-Processable Paints.

Water-based processing of graphene-typically considered as physicochemically incompatible with water in the macroscale-emerges as the key challenge among the central postulates of green nanotechnology. These problematic concerns are derived from the complex nature of graphene in the family of sp2-carbon nanoallotropes. Indeed, nanomaterials hidden under the common "graphene" signboard are very rich in morphological and physicochemical variants. In this work, inspired by the adhesion chemistry of mussel biomaterials, we have synthesized novel, water-processable graphene-polylevodopa (PDOPA) hybrids. Graphene and PDOPA were covalently amalgamated via the "growth-from" polymerization of l-DOPA (l-3,4-dihydroxyphenylalanine) monomer in air, yielding homogeneously PDOPA-coated (23 wt %) (of thickness 10-20 nm) hydrophilic flakes. The hybrids formed >1 year stable and water-processable aqueous dispersions and further conveniently processable paints of viscosity 0.4 Pa·s at 20 s-1 and a low yield stress τ0 up to 0.12 Pa, hence exhibiting long shelf-life stability and lacking sagging after application. Demonstrating their applicability, we have found them as surfactant-like nanoparticles stabilizing the larger, pristine graphene agglomerates in water in the optimized graphene/graphene-PDOPA weight ratio of 9:1. These characteristics enabled the manufacture of conveniently paintable coatings of low surface resistivity of 1.9 kΩ sq-1 (0.21 Ω·m) which, in turn, emerge as potentially applicable in textronics, radar-absorbing materials, or electromagnetic interference shielding.

Effect of ultrasonication time on microstructure, thermal conductivity, and viscosity of ionanofluids with originally ultra-long multi-walled carbon nanotubes.

The stability along with thermal and rheological characteristics of ionanofluids (INFs) profoundly depend on the protocol of preparation. Therefore, in this work, the effect of ultrasonication time on microstructure, thermal conductivity, and viscosity of INFs containing 0.2 wt% of originally ultra-long multi-walled carbon nanotubes (MWCNTs) and four different ILs, namely 1-propyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium thiocyanate, or 1-ethyl-3-methylimidazolium tricyanomethanide, was studied. The INFs were obtained by a two-step method using an ultrasonic probe. The ultrasonication process was performed for 1, 3, 10, or 30 min at a constant nominal power value of 200 W. The obtained results showed that for the shortest sonication time, the highest thermal conductivity enhancement of 12% was obtained. The extended sonication time from 1 to 30 min caused the cutting of MWCNTs and breaking the nanoparticle clusters, leading to a decrease in the average length of the nanotube bundles by approx. 70%. This resulted in a decline in thermal conductivity even by 7.2% and small deviations from the Newtonian behavior of INFs.

Remarkable Thermal Conductivity Enhancement in Carbon-Based Ionanofluids: Effect of Nanoparticle Morphology.

Transfer of the excellent intrinsic properties of individual carbon nanoparticles into real-life applications of the corresponding heat transfer fluids remains challenging. This process requires identification and quantification of the nanoparticle-liquid interface. Here, for the first time, we have determined geometry and properties of this interface by applying transmission electron cryomicroscopy (cryo-TEM). We have systematically investigated how the particle morphology of carbon-based nanomaterials affected the thermal conductivity, specific isobaric heat capacity, thermal diffusivity, density, and viscosity of ionanofluids and/or bucky gels, using a wide range of fillers, especially single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs), both with extreme values of aspect ratio (length to diameter ratio) from 150 to 11 000. Accordingly, hybrid systems composed of various carbon nanomaterials and ionic liquid, namely 1-ethyl-3-methylimidazolium thiocyanate [EMIM][SCN], were prepared and characterized. Most of the analyzed nanodispersions exhibited long-term stability even without any surfactant. Our study revealed that the thermal conductivity could be remarkably improved to the maximum values of 43.9% and 67.8% for ionanofluid and bucky gel (at 1 wt % loadings of MWCNTs and SWCNTs), respectively, compared to the pristine ionic liquid. As a result, the model proposed by Murshed and co-workers has been improved for realistic description of the concentration-dependent thermal conductivity of such hybrid systems. The obtained results undoubtedly indicate the potential of ionanofluids and bucky gels for energy management.

Rheological properties of kuzu starch pastes with galactomannans.

The paper describes the effects of galactomannans on viscoelastic properties of commercial Japanese white kuzu starch pastes. The study included morphological, thermal and rheological analyses of the biopolymer. The results obtained in the form of storage modulus G'(ω) and loss modulus G″(ω) were described by the modified fractional Kelvin-Voigt model with two springpot-type elements, created on the basis of differential calculus of fractional order and Fourier transform. It allowed to determine 17 material parameters providing a lot of additional information about structure and viscoelastic properties of the biopolymer in comparison to the classical analysis of oscillatory and creep tests. The study led to the conclusion that commercial Japanese white kuzu starch was so-called type II starch with a high pasting temperature of 75 °C and an average granule diameter equal to 10.9 µm. Rheological properties of the pastes depended on the galactose-to-mannose ratio in galactomannan molecule. The larger substitution degree, the higher viscosity, characteristic relaxation times, polydispersity index, gel stiffness, and the lower cross-linking density and average molecular weights. The presence of galactose side groups favored the hydration and immobilization of water molecules.

Fractional Generalizations of Maxwell and Kelvin-Voigt Models for Biopolymer Characterization.

The paper proposes a fractional generalization of the Maxwell and Kelvin-Voigt rheological models for a description of dynamic behavior of biopolymer materials. It was found that the rheological models of Maxwell-type do not work in the case of modeling of viscoelastic solids, and the model which significantly better describes the nature of changes in rheological properties of such media is the modified fractional Kelvin-Voigt model with two built-in springpots (MFKVM2). The proposed model was used to describe the experimental data from the oscillatory and creep tests of 3% (w/v) kuzu starch pastes, and to determine the values of their rheological parameters as a function of pasting time. These parameters provide a lot of additional information about structure and viscoelastic properties of the medium in comparison to the classical analysis of dynamic curves G' and G" and shear creep compliance J(t). It allowed for a comprehensive description of a wide range of properties of kuzu starch pastes, depending on the conditions of pasting process.