Democratization of fungal highway columns as a tool to investigate bacteria associated with soil fungi.

Bacteria-fungi interactions (BFIs) are essential in ecosystem functioning. These interactions are modulated not only by local nutritional conditions but also by the physicochemical constraints and 3D structure of the environmental niche. In soils, the unsaturated and complex nature of the substrate restricts the dispersal and activity of bacteria. Under unsaturated conditions, some bacteria engage with filamentous fungi in an interaction (fungal highways) in which they use fungal hyphae to disperse. Based on a previous experimental device to enrich pairs of organisms engaging in this interaction in soils, we present here the design and validation of a modified version of this sampling system constructed using additive printing. The 3D printed devices were tested using a novel application in which a target fungus, the common coprophilous fungus Coprinopsis cinerea, was used as bait to recruit and identify bacterial partners using its mycelium for dispersal. Bacteria of the genera Pseudomonas, Sphingobacterium and Stenotrophomonas were highly enriched in association with C. cinerea. Developing and producing these new easy-to-use tools to investigate how bacteria overcome dispersal limitations in cooperation with fungi is important to unravel the mechanisms by which BFIs affect processes at an ecosystem scale in soils and other unsaturated environments.

Cryogenic-temperature electron microscopy direct imaging of carbon nanotubes and graphene solutions in superacids.

Cryogenic electron microscopy (cryo-EM) is a powerful tool for imaging liquid and semiliquid systems. While cryogenic transmission electron microscopy (cryo-TEM) is a standard technique in many fields, cryogenic scanning electron microscopy (cryo-SEM) is still not that widely used and is far less developed. The vast majority of systems under investigation by cryo-EM involve either water or organic components. In this paper, we introduce the use of novel cryo-TEM and cryo-SEM specimen preparation and imaging methodologies, suitable for highly acidic and very reactive systems. Both preserve the native nanostructure in the system, while not harming the expensive equipment or the user. We present examples of direct imaging of single-walled, multiwalled carbon nanotubes and graphene, dissolved in chlorosulfonic acid and oleum. Moreover, we demonstrate the ability of these new cryo-TEM and cryo-SEM methodologies to follow phase transitions in carbon nanotube (CNT)/superacid systems, starting from dilute solutions up to the concentrated nematic liquid-crystalline CNT phases, used as the 'dope' for all-carbon-fibre spinning. Originally developed for direct imaging of CNTs and graphene dissolution and self-assembly in superacids, these methodologies can be implemented for a variety of highly acidic systems, paving a way for a new field of nonaqueous cryogenic electron microscopy.

Role of surfactants and salt in aqueous two-phase separation of carbon nanotubes toward simple chirality isolation.

Aqueous two-phase extraction has recently been demonstrated as a new method to separate single-wall carbon nanotubes (SWCNTs). In this work, we determined that the mechanism of separation is driven by the hydrophobicity of the surfactant, or combination of surfactants, at the SWCNT surface. This knowledge allowed us to develop a simple approach for obtaining highly enriched single-chirality suspensions in only 1 or 2 steps. These results were obtained by strategically combining multiple surfactants with different diameter-dependent binding affinities for SWCNTs and salts that readjust the surfactant structure within the mixed micelle surrounding the SWCNTs. The procedure is successfully applied to SWCNTs from different sources (CoMoCAT and HiPco) with various diameter distributions (from 0.53 to 1.2 nm). Each separation step is characterized by optical absorption, resonant Raman, and photoluminescence excitation spectroscopies. By determining the SWCNT sorting mechanism, we were able to develop a new set of parameters that separated another chirality.

Metrological Investigation of the (6,5) Carbon Nanotube Absorption Cross Section.

Using single-nanotube absorption microscopy, we measured the absorption cross section of (6,5) carbon nanotubes at their second-order optical transition. We obtained a value of 3.2 × 10(-17) cm(2)/C atom with a precision of 15% and an accuracy below 20%. This constitutes the first metrological investigation of the absorption cross section of chirality-identified nanotubes. Correlative absorption-luminescence microscopies performed on long nanotubes reveal a direct manifestation of exciton diffusion in the nanotube.

Nanoscale Thermotropic Phase Transitions Enhancing Photothermal Microscopy Signals.

The photothermal heterodyne imaging technique enables studies of individual weakly absorbing nano-objects in various environments. It uses a photoinduced change in the refractive index of the environment. Taking advantage of the dramatic index of refraction change occurring around a thermotropic liquid-crystalline phase transition, we demonstrate a 40-fold signal-to-noise ratio enhancement for gold nanoparticles imaged in 4-cyano-4'-pentylbiphenyl (5CB) liquid crystals over those in a water environment. We studied the photothermal signal as a function of probe laser polarization, heating power, and sample temperature quantifying the optimal enhancement. This study established photothermal microscopy as a valuable technique for inducing and/or detecting local phase transitions at the nanometer scales.

Direct imaging of carbon nanotubes spontaneously filled with solvent.

For the first time, cryo-TEM imaging is used to directly show spontaneous filling of carbon nanotubes immersed in a solvent in the native state at ambient conditions. Multi-walled carbon nanotubes are dissolved in chlorosulfonic acid, and the high contrast between the acid and the carbon shows the difference between filled and unfilled nanotubes.

Spontaneous dissolution of ultralong single- and multiwalled carbon nanotubes.

We report that chlorosulfonic acid is a true solvent for a wide range of carbon nanotubes (CNTs), including single-walled (SWNTs), double-walled (DWNTs), multiwalled carbon nanotubes (MWNTs), and CNTs hundreds of micrometers long. The CNTs dissolve as individuals at low concentrations, as determined by cryo-TEM (cryogenic transmission electron microscopy), and form liquid-crystalline phases at high concentrations. The mechanism of dissolution is electrostatic stabilization through reversible protonation of the CNT side walls, as previously established for SWNTs. CNTs with highly defective side walls do not protonate sufficiently and, hence, do not dissolve. The dissolution and liquid-crystallinity of ultralong CNTs are critical advances in the liquid-phase processing of macroscopic CNT-based materials, such as fibers and films.

Diameter-dependent solubility of single-walled carbon nanotubes.

We study the solubility and dispersibility of as-produced and purified HiPco single-walled carbon nanotubes (SWNTs). Variation in specific operating conditions of the HiPco process are found to lead to significant differences in the respective SWNT solubilities in oleum and surfactant suspensions. The diameter distributions of SWNTs dispersed in surfactant solutions are batch-dependent, as evidenced by luminescence and Raman spectroscopies, but are identical for metallic and semiconducting SWNTs within a batch. We thus find that small diameter SWNTs disperse at higher concentration in aqueous surfactants and dissolve at higher concentration in oleum than do large-diameter SWNTs. These results highlight the importance of controlling SWNT synthesis methods in order to optimize processes dependent on solubility, including macroscopic processing such as fiber spinning, material reinforcement, and films production, as well as for fundamental research in type selective chemistry, optoelectronics, and nanophotonics.

Spontaneous high-concentration dispersions and liquid crystals of graphene.

Graphene combines unique electronic properties and surprising quantum effects with outstanding thermal and mechanical properties. Many potential applications, including electronics and nanocomposites, require that graphene be dispersed and processed in a fluid phase. Here, we show that graphite spontaneously exfoliates into single-layer graphene in chlorosulphonic acid, and dissolves at isotropic concentrations as high as approximately 2 mg ml(-1), which is an order of magnitude higher than previously reported values. This occurs without the need for covalent functionalization, surfactant stabilization, or sonication, which can compromise the properties of graphene or reduce flake size. We also report spontaneous formation of liquid-crystalline phases at high concentrations ( approximately 20-30 mg ml(-1)). Transparent, conducting films are produced from these dispersions at 1,000 Omega square(-1) and approximately 80% transparency. High-concentration solutions, both isotropic and liquid crystalline, could be particularly useful for making flexible electronics as well as multifunctional fibres.

True solutions of single-walled carbon nanotubes for assembly into macroscopic materials.

Translating the unique characteristics of individual single-walled carbon nanotubes into macroscopic materials such as fibres and sheets has been hindered by ineffective assembly. Fluid-phase assembly is particularly attractive, but the ability to dissolve nanotubes in solvents has eluded researchers for over a decade. Here, we show that single-walled nanotubes form true thermodynamic solutions in superacids, and report the full phase diagram, allowing the rational design of fluid-phase assembly processes. Single-walled nanotubes dissolve spontaneously in chlorosulphonic acid at weight concentrations of up to 0.5 wt%, 1,000 times higher than previously reported in other acids. At higher concentrations, they form liquid-crystal phases that can be readily processed into fibres and sheets of controlled morphology. These results lay the foundation for bottom-up assembly of nanotubes and nanorods into functional materials.

Modeling the phase behavior of polydisperse rigid rods with attractive interactions with applications to single-walled carbon nanotubes in superacids.

The phase behavior of rodlike molecules with polydisperse length and solvent-mediated attraction and repulsion is described by an extension of the Onsager theory for rigid rods. A phenomenological square-well potential is used to model these long-range interactions, and the model is used to compute phase separation and length fractionation as a function of well depth and rod concentration. The model closely captures experimental data points for isotropic/liquid crystalline phase coexistence of single-walled carbon nanotubes (SWCNTs) in superacids. The model also predicts that the isotropic-biphasic boundary approaches zero as the acid strength diminishes, with the possibility of coexistence of isotropic and liquid crystalline phases at very low concentrations; this counterintuitive prediction is confirmed experimentally. Experimental deviations from classical theories for rodlike liquid crystals are explained in terms of polydispersity and the balance between short-range repulsion and long-range attractions. The predictions of the model also hold practical importance for applications of SWCNT/superacid solutions, particularly in the processing of fibers and films from liquid crystalline SWCNT/superacid mixtures.

Alignment dynamics of single-walled carbon nanotubes in pulsed ultrahigh magnetic fields.

We have measured the dynamic alignment properties of single-walled carbon nanotube (SWNT) suspensions in pulsed high magnetic fields through linear dichroism spectroscopy. Millisecond-duration pulsed high magnetic fields up to 56 T as well as microsecond-duration pulsed ultrahigh magnetic fields up to 166 T were used. Because of their anisotropic magnetic properties, SWNTs align in an applied magnetic field, and because of their anisotropic optical properties, aligned SWNTs show linear dichroism. The characteristics of their overall alignment depend on several factors, including the viscosity and temperature of the suspending solvent, the degree of anisotropy of nanotube magnetic susceptibilities, the nanotube length distribution, the degree of nanotube bundling, and the strength and duration of the applied magnetic field. To explain our data, we have developed a theoretical model based on the Smoluchowski equation for rigid rods that accurately reproduces the salient features of the experimental data.

Stable luminescence from individual carbon nanotubes in acidic, basic, and biological environments.

Aqueous surfactant suspensions of single walled carbon nanotubes (SWNTs) are very sensitive to environmental conditions. For example, the photoluminescence of semiconducting SWNTs varies significantly with concentration, pH, or salinity. In most cases, these factors restrict the range of applicability of SWNT suspensions. Here, we report a simple strategy to obtain stable and highly luminescent individualized SWNTs at pH values ranging from 1 to 11, as well as in highly saline buffers. This strategy relies on combining SWNTs previously suspended in sodium dodecylbenzene sulfonate (SDBS) with biocompatible poly(vinyl pyrrolidone) (PVP), which can be polymerized in situ to entrap the SWNT-SDBS micelles. We present a model that accounts for the photoluminescence stability of these suspensions based on PVP morphological changes at different pH values. Moreover, we demonstrate the effectiveness of these highly stable suspensions by imaging individual luminescent SWNTs on the surface of live human embryonic kidney cells (HEK cells).

Dispersions of functionalized single-walled carbon nanotubes in strong acids: solubility and rheology.

The manipulation and processing of single-wall carbon nanotubes (SWNTs) is limited by their poor solubility in most common solvents. Covalent sidewall functionalization of SWNTs provides an excellent route to improve their solubility. Here we have studied the relationship between sidewall functionalization and phase behavior of solutions of functionalized SWNTs (f-SWNTs) in strong acids. We use centrifugation in conjunction with UV-Vis-nlR spectroscopy to quantify the solubility of f-SWNTs in strong acids. We image the dispersions of functionalized tubes by polarized light microscopy. We find that adding butyl groups increases marginally the solubility of SWNTs in 102% sulfuric acid in the isotropic phase; adding 9-nonadecyne groups roughly doubles the solubility of SWNTs. Viscosity measurements in dilute solutions are sensitive to de-bundling. We compare the viscosity-concentration dependence of dilute pristine and f-SWNTs to assess whether and how functionalization promotes de-bundling and stabilizes the tubes. The phase behavior and rheology of these f-SWNTs parallels with that of pristine SWNTs; 9-nonadecylated SWNTs have higher solubility and should be easier to process.

Molecular motion of tethered molecules in bulk and surface-functionalized materials: a comparative study of confinement.

Achieving high degrees of molecular confinement in materials is a difficult synthetic challenge that is critical for understanding supramolecular chemistry on solid surfaces and control of host-guest complexation for selective adsorption and heterogeneous catalysis. In this Article, using 2H MAS NMR spectroscopy of tethered carbamates as a molecular probe, we systematically investigate the degree of steric confinement within three types of materials: two-dimensional silica surface, bulk amorphous microporous silica, and bulk amorphous mesoporous silica. The resulting NMR spectra are described with a simple two-site hopping model for motion and prove that the bulk silica network severely limits the molecular mobility of the immobilized carbamate at room temperature to the same degree as surface-functionalized materials at low-temperatures (approximately 210 K). Raising the temperature of the bulk materials to 413 K still demonstrates the effect of confinement, as manifested in significantly longer characteristic times for the immobilized carbamate relative to surface-functionalized materials at room temperature. The environment surrounding the carbonyl functionality of the immobilized carbamate is investigated using FT-IR spectroscopy, which shows the carbonyl stretching band to be equally shifted for all materials to lower wavenumbers relative to its noninteracting value in carbon tetrachloride solvent. These results suggest that electrostatic interactions between the carbonyl of the immobilized carbamate and silica surface may play an important role in confining the immobilized carbamate and nucleating the formation of a pore wall close to the immobilized carbamate during bulk materials synthesis.

Isotropic-nematic phase transition of single-walled carbon nanotubes in strong acids.

We present the first quantitative assessment of the maximum amount of nanotubes that can exist in the isotropic phase () of single-walled carbon nanotubes (SWNTs) in Brønsted-Lowry acids. We employ a centrifugation technique in conjunction with UV-vis-nIR spectroscopy to quantify , which is also the critical concentration of the isotropic-nematic transition of SWNTs in strong acids. Centrifugation of biphasic dispersions of SWNTs, that is, acid dispersions consisting of an isotropic phase in equilibrium with an ordered nematic liquid crystalline phase, results in a clear phase separation, where the isotropic phase is supernatant. Dilution of the isotropic phase with a known amount of acid followed by UV-vis-nIR absorbance measurements yields , that is, the maximum concentration of SWNTs that can exist in the isotropic phase in a given acid for a given SWNTs' length distribution. At low SWNT concentration (below 200 ppm) in superacids, light absorbance in the range from 400 to 1400 nm scales linearly with concentration. This Beer's law behavior yields calibration curves for measuring SWNTs' concentration in acids. We find that the critical concentration of the isotropic-nematic transition increases with acid strength in accordance with the previously proposed sidewall protonation mechanism for dispersing SWNTs in acids.

Macroscopic, neat, single-walled carbon nanotube fibers.

Well-aligned macroscopic fibers composed solely of single-walled carbon nanotubes (SWNTs) were produced by conventional spinning. Fuming sulfuric acid charges SWNTs and promotes their ordering into an aligned phase of individual mobile SWNTs surrounded by acid anions. This ordered dispersion was extruded via solution spinning into continuous lengths of macroscopic neat SWNT fibers. Such fibers possess interesting structural composition and physical properties.