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A study was conducted to investigate vesicle formation and general phase behavior in the cationic mixture sodium dodecyl sulfate-didodecyldimethylammonium bromide in water. The samples were left for equilibration for a number of days before phase behavior examination. An Axioplan Universal light microscope was utilized to perform light microscopy studies. In addition, the self-diffusion coefficients of water in the isotropic solutes were obtained at 25 degrees C.

[Display omitted] Aqueous graphene dispersions are usually obtainable by treating the surface of graphene chemically or physically. In these dispersions, the rheological properties (e.g., viscosity) are governed by a direct coupling to the graphene concentration, which limits their applicability. An alternative approach for dispersing graphene is trapping them in a viscoelastic-network formed by a co-dispersed charged fibrous-clay, Sepiolite. Contrary to surface treatment, the rheological properties of these dispersions are set by the clay particles. The rheology of charged-colloidal dispersions is governed by various parameters, including interparticle interactions. Hence, the rheology of the dispersion could be modulated by changing the clay surface charge without compromising the dispersed graphene concentration. The surface charge of Sepiolite was modulated either by charge-screening (by NaCl added to the solution) or by surface-charging (by attachment of highly charged ions, e.g., HexaMetaPhosphate, HMP−) and the effect on rheology and graphene concentration was assessed. In particular, loading the dispersion with HMP− yielded low viscosity, storage, and loss moduli (two orders of magnitude lower than the corresponding HMP−-free dispersion) while the graphene concentration was maintained. We demonstrate that by this charge-modulation approach, reaching the rheological requirements of different applications without compromising on graphene concentration is plausible. [ABSTRACT FROM AUTHOR]

2D materials are of interest in various applications such as energy conversion, storage, and sensing. These materials are prepared by bottom‐up or top‐down methods that are difficult to control and suffer from low yield. Synthesis in molten salt is suggested as an alternative in which the balance between exfoliation and solubility is explored. It is demonstrated that when a pellet of 2D material is insoluble in molten salt (graphite in any salt), it is exfoliated. For low solubility (MoS2 in NaCl/KCl), the 2D material nucleates and grows into a small flowerlike structure composed of thin MoS2 sheets through Ostwald ripening. For high solubility in the molten salt (MoS2 in CsCl), it forms larger flowers. Herein, the molten salt treatment of high and low surface area MoS2 (micron‐size particles and a single large pellet, respectively) is compared. The particles yielded facet MoS2 crystals through dissolution–nucleation–recrystallization process and the pellet yielded flowers. Herein, methods for synthesizing 2D materials with controllable size and shape are promoted by simple molten salt treatment that opens an avenue to the development of soluble (MoS2) and non‐soluble (graphite) materials with different morphologies in a simple and affordable way. [ABSTRACT FROM AUTHOR]

Mechanical agitation is commonly used to fragment and disperse insoluble materials in liquids. However, here we show that when pristine single-walled carbon nanotubes pre-dispersed in water are subject to vortex-shaking for very short periods (typically 10–60 s, power density ∼0.002 W mL −1 ), re-aggregation counterintuitively occurs. The initial dispersions are produced using surfactants as dispersants and powerful tip sonication (∼1 W mL −1 ) followed by centrifugation. Detailed imaging by light and electron microscopies shows that the vortex-induced aggregates consist of loose networks (1–10 2 μm in size) of intertwined tubes and thin bundles. The average aggregate size increases with vortexing time in an apparently logarithmic manner and depends on the dispersant used, initial concentration of nanotubes and size distribution of bundles. The aggregation is, nonetheless, reversible: if the vortex-shaken dispersions are mildly bath-sonicated (∼0.03 W mL −1 ), the flocs break down and re-dispersal occurs. Molecular insight for the mechanism behind this surprising phenomenon is put forth. [ABSTRACT FROM AUTHOR]

Poly(methyl methacrylate) (PMMA)/silica/cetyltrimethylammonium bromide (CTAB) composites were prepared through surfactant catalyzed free radical polymerizations at 40 °C. Fumed silica particles controlled the morphology of the polymeric composites producing porous structures. The internal structures of the porous composite were determined using temperature-modulated differential scanning calorimetry (TMDSC). The fumed silica particles were encapsulated by an incompletely covered CTAB monolayer, with a crystallization temperature, T C,CTAB = 76 °C, and a mixed PMMA/CTAB shell, with T C,CTAB = 63 °C. The fumed silica surfaces acted as inhibitors for PMMA free radical polymerizations. Much of the PMMA formed in the composites was adsorbed on the silica, as evidenced by its elevated glass transition temperature compared to bulk. The enhanced decomposition of the initiator was catalyzed by CTAB and resulted in free radical polymerization of PMMA at 40 °C, which is considerably lower than the temperatures normally used for PMMA synthesis by free radical means with thermal initiation. These lowered polymerization temperatures allow energy efficient production of composites, which can incorporate temperature sensitive materials. [ABSTRACT FROM AUTHOR]

Highlights: [•] The kinetics of solid state hydrogenation is controlled by spillover mechanism. [•] The hydrogenation rate scales with the spillover agent concentrations. [•] Carbon nanotubes and silica fumed are efficient spillover agents. [•] Carbon nanotubes type affects the hydrogenation rate. [•] The amount of metallic catalyst could be minimized by using a spillover agent. [Copyright &y& Elsevier]

Abstract: Single walled carbon nanotubes (SWNTs) with an anisotropic morphology (rod) are currently being employed as fillers in polymer matrix to produce novel nanocomposites with enhanced properties and performance in a wide variety of applications. We investigate the effect of the addition of second isotropic (spherical) filler, antimony tin oxide (ATO) particles to the anisotropic SWNT-polymer composites. Cryogenic transmission electron microscope (cryo-TEM) and scanning electron microscope (SEM) were employed to image the aqueous dispersions of the SWNTs–ATO–Latex solution and composite thin films respectively. The SEM imaging of these films shows that SWNTs (rods) tend to aggregate in the presence of ATO clusters, indicating depletion interactions between the rods and the spheres. The difference in the value of electrical conductivity of the films measured along the radial and the tangential directions to the spinning lines is probably due to the preferred orientation of the SWNTs in the matrix during the spin coating process. [Copyright &y& Elsevier]

Abstract: Rapid strides realized in the field of ordered mesoporous silica (OMS) with a well-defined pore shape and nanometric sizes, provide new gateways for the preparation of nanostructured materials having controlled shape and size with a very narrow distribution. The focus of the current review is on the synthesis of nanostructures templated by OMS either in bulk or in thin film form. The importance of electron microscopy as an indispensable technique in the structural characterization of OMS templated nanostructures, including cryo-TEM, electron tomography and HR-SEM, is highlighted in this review. [Copyright &y& Elsevier]

The in-situ exfoliation of graphite in molten NaCl–KCl salt at 750 °C yielded a homogeneous composite, from which graphene nanoplatelets (GnP) could be easily and completely separated. The GnP product displayed relatively large-size particles (12 μm, TEM, SEM, laser diffraction) and low defect density (Raman, XPS), indicating the superiority of the molten salt exfoliation approach over the conventional liquid-phase approach for producing GnP. The mechanism of GnP production involves the formation of cavities in the molten salt, such that impregnation of the graphite by the molten material facilitated gentle exfoliation of the graphite to GnP. The methodology for the in-situ production of GnP in molten salt is highly applicable in the field of thermal energy storage, where molten inorganic salts are one of the most widely used heat-transfer fluids, such as phase-change materials. In graphite-GnP-salt composite, the thermal conductivity is enhanced by more than one order of magnitude compared to the neat salt matrix, which is essential for efficient thermal energy storage applications. [Display omitted] • In-situ exfoliation of graphite in molten NaCl–KCl yields a homogeneous composite. • Graphite exfoliation mechanism involves controllable cavity-rich melt impregnation. • Graphene nanoplatelets (GnP) product can be completely separated from the composite. • The salt-GnP composite is highly applicable for thermal management applications. [ABSTRACT FROM AUTHOR]

The effect of loading a polymer matrix with more than one filler was investigated for nanocarbon-based fillers of different dimensionalities, namely, 1D carbon nanotubes (CNTs) and 2D graphene nanoplatelets (GNPs). Since both fillers have superior intrinsic mechanical, electrical and thermal properties, their use in tandem enhanced the properties of the resulting composites. The robustness , i.e., the range of nanofiller concentrations at which a substantial enhancement is achieved (considered as a weakness in single filler systems), was dramatically increased in the hybrid system as well as the thermal and electrical conductivities due to the formation of a CNT-GNP 3D structure. These measurements were in keeping with the Kreiger-Dougherty and the effective medium models, respectively. The overall performance of the hybrid composite was compared to single filler systems (using an index of performance) demonstrating the superiority of the hybrid composite in multifunctionality and robustness. [Display omitted] • Hybrid-filler has superior performance and robustness vs single-filler composite. • CNT-GNP hybrid shows enhanced fracture toughness and thermal conductivity. • 3D-filler structure (CNT-GNP) enhances the multifunctionality of the hybrid composite. • A dimensionless number determines the overall system performance. [ABSTRACT FROM AUTHOR]

Phase Change Materials (PCM) possess high heat storage density, but commonly have low thermal conductivity that results in poor heat transfer. Another common problem is the shape stabilization of the storage medium. These problems could be solved by loading the medium with thermally conductive fillers, such as graphite, and encapsulating it in a thermally conductive polymer matrix shell, hence enhancing the thermal properties of both. We suggest a ternary system in which a graphite-epoxy composite provides an encapsulating scaffold to the paraffin, which is also loaded with graphite-based filler. Various graphite-based fillers differing in sizes and geometry were explored, aiming at optimizing their intrinsic properties, such as defect density, and consequently enhancing the thermal properties of the PCM as a whole. It was demonstrated that by judicious choice of the filler, enhancement is achieved for the thermal conductivity of: (1) the shell (epoxy-graphite flakes composite) by 4000% compared to the neat epoxy; (2) the medium (paraffin-graphite flakes composite) by > 2000% compared to the neat paraffin; and (3) the integrated PCM system (paraffin-epoxy-graphite flakes composite) by 1000% compared to that of neat paraffin. The PCM composite is completely preserved during phase change cycling. • Various graphite-based fillers differing in size and geometry were explored for PCM. • Graphite flakes (GF) were found to be the best filler for the overall properties. • Ternary paraffin-GF-epoxy thermally conductive shape-stabilized system was achieved. • Properties of the ternary system were completely preserved during thermal cycling. [ABSTRACT FROM AUTHOR]

The miniaturization, integration and compatibilization of electronic devices dictate the need for efficient thermal management to prevent heat accumulation, which may reduce the operation speed and shorten their life time. Addressing this challenge requires the development of novel polymer-based composite materials with enhanced thermal conductivity. Here, we report a compression-based (25–250 bars) approach for the preparation of polymer composites loaded with carbon-based hybrid fillers, i.e., graphene nanoplatelets and graphite flakes. The carbon-based fillers contribute significantly to the thermal conductivity of the composite while boron nitride nanoparticles inhibit the electrical conductivity to avoid short circuits. An optimal thermal conductivity of 27.5 W (m K)−1 is obtained for the compressed system (measured under atmospheric pressure) for epoxy polymer loaded with 30 wt% graphene nanoplatelets and 40 wt% graphite flakes compared to 0.2 W (m K)−1 of the neat thermoset polymer. Image 1 [ABSTRACT FROM AUTHOR]

Surfactants have been widely employed to debundle, disperse and stabilize carbon nanotubes in aqueous solvents. Yet, a thorough understanding of the dispersing mechanisms at molecular level is still warranted. Herein, we investigated the influence of the molecular structure of gemini surfactants on the dispersibility of multiwalled carbon nanotubes (MWNTs). We used dicationic n - s - n gemini surfactants, varying n and s , the number of alkyl tail and alkyl spacer carbons, respectively; for comparisons, single-tailed surfactant homologues were also studied. Detailed curves of dispersed MWNT concentration vs. surfactant concentration were obtained through a stringently controlled experimental procedure, allowing for molecular insight. The gemini are found to be much more efficient dispersants than their single-tailed homologues, i.e. lower surfactant concentration is needed to attain the maximum dispersed MWNT concentration. In general, the spacer length has a comparatively higher influence on the dispersing efficiency than the tail length. Further, scanning electron microscopy imaging shows a sizeable degree of MWNT debundling by the gemini surfactants in the obtained dispersions. Our observations also point to an adsorption process that does not entail the formation of micelle-like aggregates on the nanotube surface, but rather coverage by individual molecules, among which the ones that seem to be able to adapt best to the nanotube surface provide the highest efficiency. These studies are relevant for the rational design and choice of optimal dispersants for carbon nanomaterials and other similarly water-insoluble materials. [ABSTRACT FROM AUTHOR]

Abstract We explored the mechanical and the rheological properties of cement reinforced with graphene oxide (GO, STANDARD GRAPHENE INC.) in the presence of a superplasticizer. The GO enhanced the compressive and flexural strengths of the cement matrix by 40% and 70%, respectively, at extremely low GO concentrations (<0.05 wt%). An optimal nanomaterial concentration (ONC) was observed, above which the properties deteriorate due to the formation of voids in the composite. In a comparison of different nanofiller-reinforced systems, the superiority of the cement + GO + superplasticizer system over other previously reported systems was shown by comparing the nanofiller reinforcement efficiency and a figure of merit that combines the nanocomposite's mechanical and rheological properties. [ABSTRACT FROM AUTHOR]

Aggressive miniaturization in the electronics industry demands more efficient thermal management for electronic devices. Employing the excluded volume approach, we enhanced thermal conductivity (TC) and manipulated heat dissipation in a polymer composite loaded with a thermally conductive filler—graphene nanoplatelets (GNP)—alone or supplemented with a high-volume filler (diamonds). This yielded a maximum bulk TC of 4.5 W m−1K−1 (no compression). The heat dissipation direction could be controlled by compressing (≥50 bars) the wet composite before curing, resulting in an enhancement of the cross-plane thermal conductivity (for thermal-interface materials) to 12.3 W m−1K−1. For non-compressed samples, in-plane thermal conductivity (for circuit board conformal coatings) was dominant (8 Wm−1K−1). Our holistic approach meets diverse thermal management needs. [Display omitted] • The direction of the heat dissipation could be manipulated by compression. • Composites' preparation for various thermal management applications is provided. • Generating excluded volume enhances the thermal conductivity of polymer composites. • Compressed graphene-diamonds composites yield high vertical thermal conductivity. [ABSTRACT FROM AUTHOR]

Abstract The integration of carbon nanotubes (CNTs) into a polymer matrix strongly affects the rheological behavior that in turn may hamper the overall performance of the resulting composite. Research in this topic has focused on bulk rheological properties, while here we employ NMR diffusion experiments to explore the mobility (diffusivity) of epoxy molecules when loaded with CNTs. Rheology and light microscopy indicate percolation of CNT aggregates. Those aggregates cage a substantial amount of epoxy molecules while small angle X-ray scattering indicates some rearrangement of epoxy molecules in the vicinity of the nanotubes. NMR diffusion experiments distinguish between the slow diffusion of the caged molecules and that of the free ones, and relate the fraction of the former to the macroscopic system viscosity. The demonstrated surface-induced slowing-down of diffusion is attributed to strong intermolecular π-π interactions among the epoxy molecules, and between them and the CNT surface. These findings demonstrate the utility of NMR diffusion experiments as an additional method applied to nanocomposites. Graphical abstract Image 1 Highlights • NMR diffusion aid rationalizing the rheological trends in filler-loaded resins. • CNTs influence the rheological behavior by forming a percolating network of aggregates. • The diffusive motion of epoxy molecules confined within the aggregates is strongly reduced. • The fraction of aggregate-confined epoxy correlated with the increase in the mixture's viscosity. • The slowing-down of diffusion is attributed to strong CNT-epoxy intermolecular π-π interactions. [ABSTRACT FROM AUTHOR]

Size and morphology distributions are critical to the performance of nano-drug systems, as they determine drug pharmacokinetics and biodistribution. Therefore, comprehensive and reliable analyses of these properties are required by both the US Food and Drug Administration (FDA) and European Medicines Agency (EMA). In this study, we compare two most commonly used approaches for assessing the size distribution and morphology of liposomal nano-drug systems, namely, dynamic light scattering (DLS) and cryogenic-transmission electron microscopy (cryo-TEM); an automated quantitative analysis method was developed for the latter method. We demonstrate the advantages and disadvantages of each of these two approaches for a commercial formulation of the anti-cancer drug doxorubicin - Doxil®, in which the drug is encapsulated, mostly in the form of nano-rod crystals. With increasing drug concentration, these nano-rods change the shape of the liposomes from spherical , before drug loading, to prolate (oval), post drug loading. Cryo-TEM analysis provides a detailed size distribution of both the liposomes (minor and major axes) and the nano-rod drug. Both these values are relevant to the drug performance. In this study, we show that at elevated drug concentration (2.75 mg/ml) the drug grows mainly along the major axis and that this high concentration can result, in some cases, in liposome rupture. We show that the combination of cryo-TEM and DLS constitutes a reliable tool for demonstrating the stability of the formulation in human plasma at body temperature, a characteristic that is crucial for achieving therapeutic efficacy. [ABSTRACT FROM AUTHOR]

The kinetics of hydrogen storage in magnesium can be accelerated by nanocarbon additives. In this study, we show that loading magnesium by graphene nanoplatelets (GNP) enhances the kinetics by more than an order of magnitude. The GNP presence reduces the Mg agglomeration, induced by de/hydriding, and accelerates the kinetics by connecting between Mg particles. The GNP were prepared by top-down graphite ball-milling in the presence of various organic protective agents. We found that both the molecular structure of the protective agent and the milling energy dictated the GNP properties, namely, size, thickness, defect density and specific surface area. We demonstrated how manipulation of the GNP size has a major effect on the hydrogen storage kinetics in magnesium-GNP composites. [ABSTRACT FROM AUTHOR]

• PCM-based heat sink with plate fins and spreader for transient thermal management. • Different heat sink materials and two PCM types with similar melting temperatures. • Heat spreading, temperature evolution and detailed melting patterns in the sink. • Advantageous performance of Field's metal vs. organic paraffin in heat accumulation. • Dimensional analysis generalizing power inputs and material properties. The use of phase change materials (PCMs) has gained much attention for applications of transient thermal management of electronic systems due to their high latent heat and ability to absorb heat near-isothermally. Because of their low thermal conductivity, PCMs are usually integrated with heat sinks to be used more efficiently. In this study a PCM-based heat sink with a generic structure of plate fins was investigated experimentally and numerically. The intentionally simple fin topology allowed focusing on the effects of various material properties rather than the commonly investigated geometry effects. Hence, two types of heat sink material, copper and aluminum, were examined, and two PCMs with similar melting temperatures but distinctly different thermal properties – a metallic alloy (Field's metal) and an organic paraffin (n-Octacosane), were used. Experimental findings allowed for validation of the numerical approach, used for a comprehensive parametric numerical study. The latter facilitated a more detailed investigation of the transient heat transfer processes, such as melting patterns and heat accumulation analyses, where the superior thermal properties of the metallic PCM manifested in more efficient latent heat accumulation, resulting in reduced system peak temperatures. It was found that systems with Field's metal were able to accommodate up to 80% of the energy in the form of latent heat, which is 10 percentage points higher than achieved using the organic paraffin. A dimensional analysis accounting for power inputs and material properties was conducted, and a generalized behavior was achieved for a normalized time in terms of Fourier and Stefan numbers, and thermal diffusivities ratio. [ABSTRACT FROM AUTHOR]

Mg-nanocarbon composites demonstrate fast reversible hydriding kinetics. The kinetics is strongly correlated with the structure of the added nanocarbon allotrope. We conducted a systematic exploration of the reversible hydriding kinetics of Mg upon addition of nanocarbons with different dimensionalities, namely, 1D carbon nanotubes, 2D graphene nanoplatelets and 3D activated carbon. Our findings showed that the Mg (de)hydriding rate could be tuned by the dimensionality and defect density of the nanocarbon. The resulting kinetic enhancement was explained in terms of the hydrogen spillover mechanism. The use of nanocarbons offers an alternative to the utilization of high concentrations of expensive transition-metal catalysts for hydrogen storage. [ABSTRACT FROM AUTHOR]

[Display omitted] • Nano-additives accelerated the self-healing of the textile reinforced concrete (TRC). • Decorating the textile surface with micro silica particles accelerated the self-healing process and enhanced TRC tensile strength and toughness. • Salt-cured TRC samples showed more fine cracks than tap-water-cured which promotes the self-healing process. Textile reinforced concrete (TRC) is an attractive alternative to the classic steel rebar reinforcement since the textile is stronger, more flexible, and non-corrosive compared to steel. Moreover, the TRC approach promotes the formation of multiple thin cracks pattern upon loading instead of a few wide cracks in rebar reinforcement. We found that the self-healing of these multiple thin cracks was accelerated by modifying the concrete matrix (addition of crystalline additive and alumina nanofibers) and by decorating the carbon-based textile with micro silica particles. Exposing the TRC samples to a saturated NaCl environment (as in coastal constructions) improved the bonding strength between the textile and the matrix, hence increasing the self-healing capability (compared to samples cured in tap water). [ABSTRACT FROM AUTHOR]

The loading of individual carbon nanotubes (CNTs) in matrices provides state-of-the-art nanocomposite reinforcement at low CNT concentrations. The dispersion of the CNTs in the matrix is often assisted by surfactants (termed also dispersants), which de-bundle the CNT agglomerates. Despite the critical role of the dispersants in this process, their effect on the properties of the nanocomposite has not been sufficiently studied. In the current study, we elucidate the influence of freeze-dried dispersant-CNT on the performance of polymeric and cementitious nanocomposites. We show that the dispersant (Pluronic) is crucial for exfoliating the CNTs in both types of nanocomposite, whereas it also acts as a plasticizer – thus lowering the mixture's effective viscosity – in cementitious matrices. We identify the optimal nanomaterial concentration (ONC) in each nanocomposite system, namely, the critical filler concentration in which optimal mechanical properties are obtained, and above which they degrade dramatically due to the formation of air voids that can initiate mechanical failure. Importantly, the effect of the dispersant on the nanocomposite system – and, accordingly, the origin of the resulting air voids – is different between polymeric and cementitious matrices. In polymers , a high filler concentration increases the viscosity, and, consequently, entraps air voids in the matrix during mixing. In cement , by contrast, the dispersant stabilizes the air and leads to the formation of foam in the matrix. Taken together, our findings indicate that the behavior of the dispersant throughout the composite preparation process – both in the fresh mixture and in the hardened state – should be considered when employing dispersants for use in applicative composite systems. [ABSTRACT FROM AUTHOR]

Reinforcing a fine-grained cement-based matrix with a textile fabric is an emerging approach in civil engineering, termed Textile Reinforced Mortar (TRM). We propose to load the ultra-high-performance matrix with nano-additives, i.e., a crystalline admixture (CA) or CA plus alumina nanofibers. The mix was designed to yield flow values - in the fresh state - suitable for retrofitting, and to provide high compressive strength. Examination of the durability of the TRM elements exposed to salty environments unexpectedly showed enhanced tensile strength (<81%). This is owing to the growth of salt crystals at the matrix–textile interface resulting in stronger bond strength, as imaged by scanning electron microscopy, identified by acoustic emission measurements, and validated by pull-off tests. • The developed textile reinforced mortar composites were durable in a salty environment. • Nano-additives enhanced the mortar's compressive strength and the stress at the first crack of the textile reinforced mortar. • Textile–mortar matrix bond strength was enhanced in samples cured in NaCl solution. • Salt-cured vs. tap-water-cured textile reinforced mortars showed more fine cracks with higher energy. [ABSTRACT FROM AUTHOR]