Wetting Transparency of Single-Layer Graphene on Liquid Substrates.

Graphene's wetting transparency offers promising avenues for creating multifunctional devices by allowing real-time wettability control on liquid substrates via the flow of different liquids beneath graphene. Despite its potential, direct measurement of floating graphene's wettability remains a challenge, hindering the exploration of these applications. The current study develops an experimental methodology to assess the wetting transparency of single-layer graphene (SLG) on liquid substrates. By employing contact angle measurements and Neumann's Triangle model, the challenge of evaluating the wettability of floating free-suspended single-layer graphene is addressed. The research reveals that for successful contact angle measurements, the testing and substrate liquids must be immiscible. Using diiodomethane as the testing liquid and ammonium persulfate solution as liquid substrate, the study demonstrates the near-complete wetting transparency of graphene. Furthermore, it successfully showcases the feasibility of real-time wettability control using graphene on liquid substrates. This work not only advances the understanding of graphene's interaction with liquid interfaces but also suggests a new avenue for the development of multifunctional materials and devices by exploiting the unique wetting transparency of graphene.

Doping Engineering of Single-Walled Carbon Nanotubes by Nitrogen Compounds Using Basicity and Alignment.

Charge transport properties in single-walled carbon nanotubes (SWCNTs) can be significantly modified through doping, tuning their electrical and thermoelectric properties. In our study, we used more than 40 nitrogen-bearing compounds as dopants and determined their impact on the material's electrical conductivity. The application of nitrogen compounds of diverse structures and electronic configurations enabled us to determine how the dopant nature affects the SWCNTs. The results reveal that the impact of these dopants can often be anticipated by considering their Hammett's constants and pKa values. Furthermore, the empirical observations supported by first-principles calculations indicate that the doping level can be tuned not only by changing the type and the concentration of dopants but also by varying the orientation of nitrogen compounds around SWCNTs.

Doping of carbon nanotubes by halogenated solvents.

Carbon nanotubes (CNTs) play a unique role in the area of flexible conductors as they have remarkably high electrical conductivity and bend easily without deformation. Consequently, CNTs are commonly deposited on substrates as conductive tracks/coatings. Halogenated solvents are often employed to facilitate the deposition process because they dry rapidly due to their high volatility. In this work, we report that halogenated solvents can dope CNTs considerably. The study showed that the use of dichloromethane, chloroform, or bromoform for the CNT deposition significantly impacts the chemical potential of the material, thereby modifying its charge transport characteristics. As a consequence, up to four-fold improvement in electrical conductivity is noted due to doping.

Tuning wettability and electrical conductivity of single-walled carbon nanotubes by the modified Hummers method.

Partial oxidation of nanocarbon materials is one of the most straightforward methods to improve their compatibility with other materials, which widens its application potential. This work studied how the microstructure and properties of high crystallinity single-walled carbon nanotubes (SWCNTs) can be tailored by applying the modified Hummers method. The influence of temperature (0, 18, 40 °C), reaction time (0 min to 7 h), and the amount of KMnO4 oxidant was monitored. The results showed that depending on the oxidation conditions, the electronic characteristics of the material could be adjusted. After optimizing the parameters, the SWCNTs were much more conductive (1369 ± 84 S/cm with respect to 283 ± 32 S/cm for the untreated material). At the same time, the films made from them exhibited hydrophilic character of the surface (water contact angle changed from 71° to 27°).

Enhancing thermoelectric properties of single-walled carbon nanotubes using halide compounds at room temperature and above.

Carbon nanotubes (CNTs) are materials with exceptional electrical, thermal, mechanical, and optical properties. Ever since it was demonstrated that they also possess interesting thermoelectric properties, they have been considered a promising solution for thermal energy harvesting. In this study, we present a simple method to enhance their performance. For this purpose, thin films obtained from high-quality single-walled CNTs (SWCNTs) were doped with a spectrum of inorganic and organic halide compounds. We studied how incorporating various halide species affects the electrical conductivity, the Seebeck coefficient, and the Power Factor. Since thermoelectric devices operate under non-ambient conditions, we also evaluated these materials' performance at elevated temperatures. Our research shows that appropriate dopant selection can result in almost fivefold improvement to the Power Factor compared to the pristine material. We also demonstrate that the chemical potential of the starting CNT network determines its properties, which is important for deciphering the true impact of chemical and physical functionalization of such ensembles.

Impact of Synthesis Parameters of Multi-Walled Carbon Nanotubes on their Thermoelectric Properties.

Carbon nanotubes have been intensively researched for many years because of a wide array of promising properties that they have. In this paper, we present the impact of synthesis parameters on thermoelectric properties of nanocarbon material. We conducted a number of syntheses of multi-walled carbon nanotubes (MWCNTs) at different temperatures (800 and 900 °C) using various amounts of catalyst (2%, 5.5%, and 9.6%) to facilitate the process. We also tested the influence of injection rate of precursor and the necessity of material purification on thermoelectric properties of MWCNTs. The electrical conductivity, thermal conductivity, and Seebeck coefficient were measurement for all samples. Based on these parameters, the values of Power Factor and Figure of Merit were calculated. The results show that the most important parameter in the context of thermoelectric properties is purity of employed MWCNTs. To obtain appropriate material for this purpose optimum synthesis temperature and appropriate content of the catalyst must be selected. The study also reveals that post-synthetic purification of nanocarbon is essential to produce an attractive material for thermoelectrics.

Simple Method to Improve Electrical Conductivity of Films Made from Single-Walled Carbon Nanotubes.

Despite the widespread use of sonication for individualization of nanomaterials, its destructive nature is rarely acknowledged. In this study, we demonstrated how exposure of the material to a hostile sound wave environment can be limited by the application of another preprocessing step. Single-walled carbon nanotubes (CNTs) were initially ground in a household coffee grinder, which enabled facile deagglomeration thereof. Such a simple approach enabled us to obtain high-quality CNT dispersion at reduced sonication time. Most importantly, electrical conductivity of free-standing films prepared from these dispersion was improved almost fourfold as compared with unground material eventually reaching 1067 ± 34 S/cm. This work presents a new approach as to how electrical properties of nanocarbon ensembles may be enhanced without the application of doping agents, the presence of which is often ephemeral.

Probing the mechanics of aqueous two-phase extraction using large diameter single-walled carbon nanotubes.

We have demonstrated that large diameter (1.8 ± 0.4 nm) carbon nanotubes (CNTs) can be separated by means of the aqueous two-phase extraction (ATPE). This rapid and convenient tool has enabled us to isolate fractions of particular CNT diameter distribution. We have shown how a range of parameters can be used to fine tune the characteristics of the isolated material. Interestingly, by varying the pH of the medium, we have suppressed the extraction of low diameter CNTs and only large diameter CNTs were obtained. A number of other factors such as selected surfactant concentration steps, temperature or amount of starting CNT material have been found to have a significant effect on the end result of the CNT differentiation. The findings have provided us with more insight regarding the underlying mechanics of ATPE for processing polydisperse CNT mixtures.

Unexpectedly strong hydrophilic character of free-standing thin films from carbon nanotubes.

We report on the development of a method of formation of hydrophilic carbon nanotube (CNT) films. The technique is simple, straightforward and does not require specialized equipment or use of harsh chemical compounds. Elimination of the need for oxidizing agents has paramount implications because it preserves the inherent CNT properties. A reference study, in which the traditional method of oxidation of CNTs was used to introduce functional groups, gave smaller reduction of water contact angle and made a negative influence on the surface chemistry. From the practical point of view, this method is an important step towards implementation of CNTs in the real life by making them more compatible with interface materials. Interestingly, the method gives high level of control over the surface character of CNT films and hydrophilic character can be precisely patterned where required.