Current Nanoscience - Volume 6, Issue 2, 2010

The combination of patterning techniques, such as scanning probe based lithography, with the “grafting from” approach of polymer brushes opens the possibility to create structured functional substrates for the fabrication of sensors, electronic devices and others. The use of the surface-initiated ring-opening polymerization furthermore allows the introduction of biodegradable and technologically relevant polymer systems. These surface templates were obtained by the electro-oxidation of an n-octadecyltrichlorosilane coated silicon substrate and were subsequently functionalized with a second functional trichlorosilane, self-assembled onto the oxidized areas. A two step reaction sequence led to the formation of -OH functionalities. These hydroxy moieties served as covalently linked initiator templates for the ring-opening polymerization of L-lactide. Via this technique polymer brushes could be obtained with a height in the order of 30 nm. The created structures were further characterized by FT-IR and XPS spectroscopy as well as AFM microscopy.

Investigations on gas adsorption in nanostructures are important for potential applications such as fuel cell, gas sensor, hydrogen storage etc. Of all nanomaterials, carbon (CNTs) and boron nitride nanotubes (BNNTs) are analyzed widely, since they are porous, having large surface area and high thermal stability. It is interesting to note that while CNTs exhibit both semiconducting and metallic behaviour, BNNTs show only semiconducting nature. Factors like topological defects, doping and functionalization are observed to enhance the effect of adsorption in these nanotubes. We have considered physisorption of H2, N2 and O2 in armchair (5,5) nanotubes of both carbon and boron nitride and estimated the binding energies through simulation. To study the role of defects, we have introduced a combination of an octagon and a pair of pentagon (5-8-5) called divacancy defect in the hexagonal structure and calculated adsorption binding energy (Eads) of gas molecules at the defected site. We could observe 59.72% increment in Eads in defected CNTs and 122.7% enhancement in defected BNNTs compared to defect-free tubes for hydrogen. With nitrogen molecule as adsorbate, we found 58.49% and 84.13% increase in Eads in defected CNTs and BNNTs respectively. The results lead to the conclusion that defects plays a vital role on physisorption in both carbon and boron nitride nanotubes.

The hyper Wiener index of a molecular graph is defined as one half of the sum of the distances and square distances between all (unordered) pairs of vertices of the graph. In this paper we find an exact formula for calculation of the hyper Wiener index of nanotubes which have square and octagon structure and denoted by C4C8(S) nanotubes.

The development of carbon nanotubes (CNTs) for biomedical and biotechnological applications has gained great promise recently, especially for their interesting use in the delivery of therapeutically active molecules to targeted cells. The interaction between cells and this nanomaterial is a critical feature that is responsible for the pharmacological effect as well as for any eventual toxicity. With respect to the latter aspect, in this manuscript we have evaluated a few parameters that seem to be involved in the cytotoxic profile of CNTs (both Single-walled (SWCNTs) and Multi-walled (MWCNTs) nanotubes), such as their sidewall functionalization, tubes' length, solubility, concentration and purity. Among them, we identified the last as the most crucial factor: we have shown that our ultrapure, totally dispersible, carbon nanotubes not only display lack of toxicity in the range of concentrations normally used (10-150 μg/ml), but they also pave the way for an extensive use of this material for several biomedical purposes.

The pentagonal carbon nanocones are constructed from a graphene sheet by removing a 60 ° wedge and joining the edges produces a cone with a single pentagonal defect at the apex. In this paper, the Wiener indices of these nanocones are computed generally by a new graph theoretical method, for the first time. We prove that our method is general and it is possible to apply for other nanostructures.

The rheological and electrical properties of suspensions of carbon nanotubes in an uncured epoxy resin were investigated by means of shear rheology and impedance spectroscopy. It was found that above an onset CNT weight fraction (0.1 wt%), the steady viscosity increased with CNT loading and presented a shear thinning behaviour. The concentration dependence of viscosity changed from a power law to an exponential with increasing shear rate, indicating a loss of interaction between aggregates and CNT network breakage. The fluid-to-solidlike and insulator-to-conductor transitions occurred in the same CNT weight fraction range between 0.5 and 0.6 wt %. The correspondence of these transitions was explained by the reduction of contact resistance between CNT by stiffening of the CNT network leading to improved electronic transport.

CuS nanocrystals in hexagonal structure have been synthesized by mechanical alloying the elemental Cu and S powders. CuS compound was formed through the reaction of Cu + S → CuS, which was initiated only 100 seconds after the mechanical alloying process started. XRD pattern suggests that pure CuS nanocrystals in hexagonal structure were obtained after mechanical alloying process was carried out for 40 hours. The as-milled CuS nanocrystals were subsequently capped with organic-inorganic compsite ligand of trioctylphosphine oxide / trioctylphosphine / nitric acid (TOPO/TOP/NA). The morphology of the as-milled and capped CuS nanocrystals has been studied by transmission electron microscope (TEM). The size of capped CuS nanocrystals ranges from 2 nm to 10 nm. The capped CuS nanocrystals show similar optical properties to the CuS nanocrystals prepared by wet chemical process, the absorption peaks for capped CuS nanocrystals locate within the wavelength range of 656 to 665 nm.

A ferromagnet-metal composite, La0.9Sr0.1MnO3-Pt (nano-crystal)-La0.9Sr0.1MnO3, was executed by r.f. magnetron sputtering deposition. It was clearly shown that the metallic Pt nano-crystals were formed in the La0.9Sr0.1MnO3 (LSMO) matrix. The decrease of Curie temperature by the introduction of Pt nano-crystals into LSMO thin films was observed, which was attributed to the induction of the magnetic inhomogeneity or spin disorder in the films. Moreover, the spin alignment in the normal direction of the films was significantly affected by the insertion of the ultrathin layers of Pt nano-crystals. The metal nano-crystals embedded in the LSMO matrix led to a better connectivity and provided an easier pathway for electron transport between grains.

Nanomechanical response of indented aluminum/titanium (Al/Ti) multilayered films were characterized using an Auger electron spectrometer, focused ion beam (FIB) machining, and transmission electron microscopy (TEM). The pure and multilayered films on Si(100) substrates were prepared using the radio frequency magnetron sputtering process. The empirical Hall-Petch relationship and its reverse effect on nanoindentation load-displacement curves, hardness, and Young's moduli were discovered in individual layers at thicknesses of 28, 14, and 7 nm, respectively. The contributions of atomic sliding grain boundaries and their Al/Ti interfaces were studied. The Hall-Petch effect was seen in thickness of about 3.5 nm for its well blending at such nanometer scale.

In this study, a cell labelling method is presented using biocompatible europium doped hydroxyapatite (Eu-HAP) inorganic nanoparticles. Eu-HAP nanoparticles were successfully prepared by precipitation method and utilized to label Bel-7402 human liver cancer cells as fluorescent probe. After Eu-HAP nanoparticles were internalized by cells, the strong green fluorescence and the red fluorescence were observed with excitation of blue light and green light respectively. Results show that the Eu-HAP nanoparticles exhibit the potential to become valuable biocompatible fluorescent labelling material in biological studies.

Nanoemulsions/microemulsions are thermodynamically stable transparent (translucent) isotropic dispersions of oil and water stabilized by an interfacial film of surfactant and cosurfactant molecules having the droplet size of less than 100 nm. Because of their thermodynamic stability, they can be manufactured without utilizing high input of energy. In an attempt to enhance transdermal/topical drug delivery of anti-inflammatory agents (AIs), nanoemulsions/microemulsions have been more frequently employed over the recent years. Nanoemulsions/microemulsions have been shown to be superior for transdermal/topical delivery of particularly lipophilic compounds as compared to conventional vehicles such as emulsions, suspensions, gels and liposomes. Nanoemulsions/microemulsions exhibit excellent solubility properties. These vehicles also act as transdermal permeation enhancers without utilizing additional permeation enhancers. In this review transdermal and topical delivery of AIs both in vitro as well as in vivo has been summarized and reviewed.

Synthesis of new generation of agrochemicals of phenoxyherbicides-type, namely 2-chloro- (2CPA) and 2,4,5- trichlorophenoxy acetates (TCPA) were accomplished by hybridization of the phenoxyherbicides into zinc-aluminium-layered double hydroxide interlamellae for the formation of new nanohybrids of 2CPA and TCPA, labeled as N2CPA and NTCPA, respectively. Basal spacing expansion from 8.9 Å in the layered double hydroxide (LDH) to 18.5 and 26.2 Å in the resulting N2CPA and NTCPA nanohybrid, respectively, together with FTIR, CHNS and TGA/DTG data support that the phenoxyherbicides were successfully intercalated into the layered double hydroxide inorganic interlayers. The release of the phenoxyherbicides from their nanohybrids at various pHs can be expressed by parabolic diffusion at the beginning of the process, but the release data for the whole process followed the pseudo-second order equation. The release process was found to be pH-dependent, in the order of pH 12 > 3 > 6.25. In addition, the release time for TCPA is longer than 2CPA, suggesting a stronger interaction of TCPA than 2CPA with the layered double hydroxide inorganic interlayer. This study indicates the potential application of zinc-aluminium-layered double hydroxide as the matrix of the controlled release formulation of agrochemicals such as 2-chlorophenoxyacetic acid and 2,4,5-trichlorophenoxyacetic acid.

We report the construction of titania contained opal and inverse opal structures by using colloidal crystals as templates which were self assembled from poly(allylamine hydrochloride) (PAH)/poly(acrylic acid) (PAA) multilayer film coated polystyrene (PS) particles. By infiltrating a titania precursor titanium (IV) bis (ammonium lactato) dihydroxide (TALH) into the polyelectrolyte (PE) multilayer film followed by calcination at different temperatures, PE/TiO2 composite opal or inverse opal structures were obtained. The thickness of the titania coating on colloidal crystals or the wall thickness of titania inverse opals could be controlled by varying the coating thickness of the PE film on PS particles during the layer-by-layer (LbL) deposition process. The crystalline phase of titania inverse opals was determined by the heating temperature. However, titania inverse opals with pure rutile phase lost their ordered structures due to the formation of large rigid rutile titania crystals during the phase transfer process. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), reflectance spectroscopy and X-ray diffraction were employed to characterize the formed structures and titania crystal phases.

Zinc nitrate precipitated with NaOH solution under double-jet conditions produced uniform nanostructured zinc oxide particles containing stacked nanoplates at 80 °C in the presence of starch sodium octenyl succinate (SSOS). In the absence of SSOS, nonuniform agglomerated ZnO particles and hexagonal nanorods were obtained. The presence of SSOS provided important hints on particle formation and confirmed that submicronic particles resulted from nanocrystals oriented aggregation. The formation kinetics of layered structures was followed by SEM observations, suggesting that they result from a rapid aggregation of about 40nm primary nanoparticles followed by rearrange into organized layered structures. Oxide materials with this shape are especially interesting for catalytic, piezoelectric and sensing applications. The stacked ZnO exhibits a surprisingly good activity for aqueous photocatalytic decompositions of 4-chlorophenol under visible light.

A thorough understanding of the electrical transport behavior of large-area and nano-scale contact devices employing thin film homo- or hetero-junctions is critical to designing and fabricating high-performance optoelectronic devices. We investigate and discuss the electrical transport properties of ZnO diodes measured on macroscopic and nano-scale contacts based on current understanding of the field. The ZnO thin film based macroscopic and nano-scale diodes are the Au/ZnO/Si and conductive atomic force microscopy tip/ZnO/Si structures, respectively. The four large-area contact diodes exhibited different electrical properties such as ideality factor, turnon voltage and breakdown voltage, whereas the nano-scale contact diodes exhibited similar electrical property but different from the four large-area contact diodes. The electrical transport across the nanoscale contact junctions is believed to be dominated by tunneling; whereas in large-area contact diodes, it is predominant either by thermionic emission or tunneling depending on the doping type and dopant concentration of the Si substrates. These results provide an experimental demonstration and are expected to yield insights that are necessary for designing practical, high-performance nanophotonic devices based on ZnO thin films or nanostructures.

A common challenge in the X-ray nanotomography of porous media, such as fuel cell gas diffusion layers (GDLs), is to binarize nanotomography greyscale images in order to differentiate between solids and voids for structural characterisation and numerical flow analysis. In the process threshold determination is critical. This paper presents a study on determination of and fine-tuning threshold value based on comparison of material porosity and average fibre diameter obtained from nanotomography images with porosity data from density experiments and average fibre diameter achieved from scanning electron microscopy images respectively. The more accurate 3D reconstructed model is then used to calculate pore size distribution and average pore size, while the gas permeability of the representative 3D binary images are calculated using a single phase Lattice Boltzmann (LB) model in the D3Q19 regime.