Current Nanoscience - Volume 6, Issue 1, 2010

During the last decade there has been a growing attention to nanoscaled materials and to the related technologies to produce them. The problems to overcome in the manufacturing of these kinds of items increase dramatically on decreasing the dimension of the devices. In this sense, the scientific research has been strongly stimulated to try to improve and optimize all the critical issues. One of the most attractive fields in nanomanufacturing is related to nanoimprinting, i.e. to the possibility to transfer a nanoscaled pattern from a mold to another substrate. In this technology, among the others, there are two main critical steps: the preparation of a good mold and the use of a correct releasing agent to reduce the sticking between the mold and the imprinted substrate. In this review paper the authors will describe the most recent advances on the preparation of the mold, including the studies on the releasing agents used during the manufacturing.

Carbon nanotubes represent one of the most important materials in nanoscience and nanotechnology today. The exceptional properties that these materials possess open new fields in science and engineering. Additionally, the chemistryassociated to these materials starts to play an important role, inasmuch, new moieties insert by different chemical routes, inside and outside of carbon nanotubes surfaces, have shown able to modify their structure and properties. To this date, new properties have been found in chemically-modified nanotubes and diverse potential applications are suggested for these materials. One of the most frequent applications for these carbon materials is their inclusion as reinforcement in polymer matrices, due to the amazing structural, mechanical, electrical, chemical and thermal properties that carbon nanotubes possess, suggesting that these materials are ideal to produce new polymer nanocomposites. In this context, carbon nanotube nanocomposites have been developed by numerous research groups around the world aiming to produce new novel strong and light composite materials. Also, electrical conductivity and thermal properties have been studied for this kind of nanocomposites. However, new challenges to create a new age of multifunctional composite materials with these nanometric forms arise and, therefore, the study of new properties in these nanocomposites has increased significantly in the last few years. In this review we discuss a range of methods to properly utilize nanotubes in poymer-based composites, from the solubility behavior of carbon nanotubes, the processing methods to develop carbon nanotube polymer composites, interactions produced between carbon nanotubes and polymer grafted, to the most recent results on the mechanical and thermal properties of carbon nanotubes polymer composites, synthesized with different types of carbon nanotubes. In addition, we discuss the effect of different chemical modifications on nanotubes, with special focus on those developed to improve the compatibility between these nanostructures and engineering polymers, as well as their effect on the final composites properties. The significance of understanding, enhancing and controlling the behavior at the interface between nanotubes and polymer matrices towards the development of novel multifunctional applications with these composites, is also discussed in detail.

Polymer-ceramic composites having polyvinylidene fluoride (PVDF) matrix filled with nanocrystalline barium titanate (BT) and multiwalled carbon nanotubes (MWNTs) were prepared by sonicated solution mixing method. The dielectric permittivity and electrical conductivity of such hybrids were measured over a wide range of frequencies. The results showed that the dielectric permittivity of PVDF/BT 50/50 composite at room temperature increases from ∼ 94 to ∼ 620 at 1 kHz by adding a small amount (2.5 vol. %) of nanotubes. Moreover, the dielectric permittivity of this hybrid composite tended to increase with increasing temperature and reached an apparent maximum value of 780 at 122 °C. The excellent dielectric performance of the composite was analyzed in terms of the percolation and dielectric relaxation concepts.

In this work, ZnO nanostructures synthesized by thermal evaporation of zinc oxide (ZnO) and carbon nanotubes (CNTs) on silicon substrate with sputtered Ag catalyst on are investigated. The multi-wall CNT powder made by chemical vapor deposition was mixed with ZnO powder with a ratio of 1:1 by mole. The mixture was then evaporated under argon flow in a horizontal tube furnace with source temperature of 950 C. Structural characterization by scanning electron microscopy showed that ZnO polypods including tripods, tetrapods, multipods with triangular nanobelts and nanoneedles extending from each leg were formed while short nanorod and nanoparticle ZnO structures were obtained by ZnO-graphite evaporation under the same condition. In addition, considerable carbon content in ZnO nanostructure was observed by energy dispersive x-ray spectrometry. Transmission electron microscopy and x-ray diffraction confirmed single crystal structure and dominant [101] crystal facet. Vapor-solid mechanism and oxidation in high carbonaceous ambient are proposed as mechanisms for the formation of ZnO polypod by ZnO-CNT thermal evaporation. Moreover, ZnO nanostructures have an interesting flat green luminescent band between 480 and 530 nm and plausible explanation based on carbon doping and multi-dimensional structure is proposed to be responsible for such characteristic.

An easy strategy was developed for the water-soluble multi-walled carbon nanotubes (MWCNTs) without the length cutting of MWCNTs via the ultrasonic-assisted chemical functionalization with a redox couple ammonium persulfate/diethanolamine at room temperature. The Fourier transform infrared spectroscopy, Raman and X-ray photoelectron spectroscopy analysis of the functionalized MWCNTs conclusively showed that diethanolamino groups were covalently attached onto the sidewalls of the MWCNTs. The thermogravimetric analysis result showed the surface functional group content of the functionalized MWCNTs was 0.66 mmol/g. And the transmission electron microscope analysis showed that the MWCNTs were exfoliated into individual nanotubes. The resultant MWCNTs were dispersed easily in water and the dispersion was stable for more than 4 days.

In situ chemical polymerization is used to prepare composites of multiwalled carbon nanotubes (MWCNTs) that are either wrapped with polyaniline (PANI) (MWP), or with perpendicular aligned PANI (MAP). Systematic study of morphology, composition, structure, thermal stability, and electrical properties is performed as a function of temperature to understand the composite formation. Orientation of PANI chains and the direction of electron transport in MWCNTs and PANI play an important role in conductivity. At room temperature (RT), MWP, wherein PANI and MWCNTs are aligned parallel, exhibits high conductivity, which decreases gradually above RT. Contrary in MAP, the conductivity at RT is lower because of the perpendicular alignment of PANI on the MWCNTs. However, it increases with the increase in temperature, as short chains of PANI switchover and get adsorbed onto the MWCNTs forming a near parallel orientation, in which, aromatic amines of PANI graft to the MWCNTs. Eventually, morphology becomes a dominating factor which influences the conductivity and thermoelectric properties of the composites, above 150 °C. The results show that the morphology, interfacial contact, and the dopant concentration are the key factors in governing the conductivity of MWP and MAP composites at RT and above. These observations are supported by X-ray diffraction, X-ray photoelectron spectroscopy, and time of flight-secondary ionization mass spectrometry study.

Development and progression of breast cancer can be caused by increased estradiol activity, which stimulates cell proliferation. Inhibitors of type 1 17β-hydroxysteroid dehydrogenase (17β-HSD) enzyme inhibit estradiol biosynthesis and therefore have potential anticancer activity. In this study two new trans-cinnamic acid esters were established as inhibitors of the human recombinant type 1 17β-HSD enzyme. Studied compounds are poorly water soluble and have low stability in aqueous medium. Free inhibitors were tested on T-47D cells, which express the target enzyme, but did not exert any biological effect up to 100 μM. Therefore, novel poly(η- caprolactone) nanoparticles loaded with the inhibitors were formulated and their effects on T-47D cells were investigated. Prepared nanoparticles had regular spherical shape and mean diameters in the range of 130-170 nm, low polydispersity, high zeta potential and entrapment efficiency. Effective uptake of nanoparticles into T-47D breast cancer cells was confirmed, indicating the possibility to deliver incorporated inhibitor into the cell cytoplasm, where it is released and inhibits the target enzyme. Furthermore, the effect of delivered inhibitors resulted in reduced cell viability and changes in cell morphology. It is anticipated that engineering of efficient delivery system for new poorly soluble inhibitors led to a significant improvement of their biological activity and stability.

Using a surfactant-mediated method, nanocrystalline titanium dioxide with a high BET surface area was generated within the template of the nonionic surfactant micelle assembly from the anhydrous metal chloride, TiCl4. The results indicate that the block copolymer can control the particle size and inhibit the agglomeration of anatase titanium dioxide in the calcining process, and simultaneously enhance phase transformation from amorphous titanium dioxide to anatase phase. The pore diameter and the BET surface area of the material, evaluated from the N2 adsorption-desorption isotherm, indicate average pore diameter of about 6.6 nm, and BET surface area about 115.04 m2/g for calcination at 400°C. The resulting particles were highly crystalline and largely monodisperse oxide particles in the nanometer range of 18-22 nm.

Novel layered organic-inorganic hybrid materials consist of molybdenum oxide have been synthesized using three aminohydroxy ligands; diethylenetriamine, 2-(2-aminoethoxy) ethanol and 2-(2-aminoethylamino) ethanol. Different analysis methods have been utilized for understanding of the bonding nature between the organic and inorganic components and how the insertion of organic groups affects the structure of the inorganic layers (MoO3). Moreover, the influence of these different structures on the catalytic performance of oxide is discussed. The coordination of organic molecules to molybdenum center shows a decrease in the Mo=O bond strength, as might be characteristic in catalytic reaction. Furthermore, fabrication of the organized nanoplatelets of molybdenum oxide is achieved by calcinations of these hybrid materials at 600 °C. Somewhat oriented nanoplatelets are viewed with different catalytic activity according to their surface areas. The higher intercalated material shows higher surface area in its calcined material.

Present study describes a simultaneous and highly reproducible, large-scale, one-pot, template free synthesis of nearly homogeneous and blue luminescent CdSe nanoparticles (NPs) in a single reaction at 50°C by wet chemical method. The method is simple, inexpensive and ensures almost complete utilization of the precursors. The product was well characterized by X-ray diffraction, UV-Vis. spectroscopy, Fourier transform infrared spectroscopy and Transmission electron microscopy. X-ray diffraction pattern indicates that CdSe NPs possess a Wurtzite (Hexagonal) structure. Systematic particle size dependent ‘blue shift’ is observed in optical absorption edge. Transmission electron microscopy showed that the particles diameters are in the range of 5 – 8 nm.

Zn1–xCdxS Nanoparticles with varying Cd concentration were synthesized via co-precipitation technique at 280 K. Despite the analogous size, the nanoparticles with different Cd content exhibit composition-dependent absorption resulting from the distinguished band gap. Due to size effect Zn1–xCdxS nanoparticles, self activated PL band shifted to higher energies compared to the absorption band of bulk counterpart. Origin of the PL emission bands are investigated via fluorescence lifetime measurement. Decay time constant is found in nano second regime and is attributed to the spatial confinement of photo generated electron-hole pairs.

Though it has been established that ZnO tetrapods can be synthesized by heating Zn in air, it is advantageous to grow tetrapods with legs of different morphologies with different lengths. Here, we report the large scale synthesis of ZnO tetrapods by heating Zn in air ambient. The parameters that control the diameter, length, and morphology of tetrapods are identified. It is shown that the morphology and dimensions of the tetrapods depend not only on the vaporization temperature but also on the temperature gradient of the furnace. The controlled synthesis procedure and the key parameters that influence the morphology are discussed.

Recent theoretical progress in understanding the effect of noble metal nanoparticles on the luminescent properties of europium complex was reviewed. The observed enhancement fluorescence results from surface-enhanced fluorescence (SEF) based on the surface plasmon resonance (SPR) of noble metal nanoparticles. And the observed quenching fluorescence is attributed to the re-absorption of surface plasmon resonance and noble metal nanoparticles scattering. And then the enhancing and quenching effects strongly depend on size, shape, concentration, surrounding medium of noble metal nanoparticle and the structure of europium complex. Furthermore, the mechanism of surface-enhanced fluorescence, and physical process between noble metal nanoparticles and europium complex were also discussed in detail. These discussions are very important to further improve enhancement factor, which is key to application in optical materials for the surface-enhanced fluorescence phenomenon of noble metal nanoparticles.

Hydrothermal conversion of Degussa P25 into pure rutile has been investigated at 180°C under acidic conditions. Detailed characterizations of the hydrothermal products were achieved via XRD, TEM, BET, Raman scattering, and UV-vis absorption spectroscopy. The results show that the conversion process is a zero order reaction with a constant anatase conversion rate of ∼1.469 wt%/h. The existent ∼17.9 wt% of rutile in the starting P25 powder does not seem to appreciably seed the phase transition or lead to an epitaxial growth of the rutile crystals. Quasi-equiaxed rutile nanocrystals (∼41 nm, ∼31.5 m2/g), a morphological form most difficult to synthesize via soft-chemical processing, have been obtained at a HNO3/TiO2 molar ratio of 12. Higher acidity or the presence of Cl- tends to yield rutile nanorods, and the effects of Cl- are more significant. These phenomena have been deciphered by considering the solution chemistry of the titanium ionic species and the construction mechanisms of the rutile lattice. Both the equiaxed and the rodlike rutile nanocrystallites were found to be oxygen stoichiometric and possess an indirect interband transition energy of ∼2.93 eV. The rutile nanocrystals obtained via this strategy may find applications as nano-whiteners in cosmetics and pigments.

Stochastic parameters of self–agglomerated metallic nanoparticles on a dielectric film surface were studied using atomic force microscopy (AFM) analysis. In this regard, the rough surfaces including the nanoparticles were analyzed and characterized using structure function, roughness exponent and power spectrum density of the AFM profiles and their gradients, for different metal concentrations and heat treatment temperatures. The diffusion parameters, such as activation energy, of the nanoparticles initially accumulated on the surface into a porous and aqueous silica thin film were obtained using the AFM spectral analysis of the profiles and their gradients. It was found that the tip convolution effect can dramatically change the diffusion parameters obtained using the surface roughness analysis of the normal profiles. However, use of the surface roughness analysis of gradient of the profiles resulted in a nearly independent tip convolution effect procedure to study the kinetics of the nanoparticles into the silica film. Based on the obtained results, a brief discussion on the mechanism of diffusion process was also proposed.