Preparation and characterization of polycarbonate/multiwalled carbon nanotube nanocomposites.

A polymer nanocomposite was produced by ultrasonic-assisted dispersion of multiwalled carbon nanotubes (MWCNTs) in a polycarbonate matrix using p-xylene and dichloromethane as the solvents. The filler loading was varied from 1 to 3 wt % in order to examine the effect of MWCNTs on the structure and properties of the composites. The nanocomposites were characterized by DSC, DTA, TGA, UV-vis, FTIR and Raman spectroscopy to evaluate the changes induced by the filler in the polymer matrix. UV-vis, FTIR and Raman spectroscopy measurements confirmed the presence of the dispersed phase in the composite films, while TGA and DSC analysis of the nanocomposites revealed enhanced thermal stability and decreased crystallinity, respectively, as compared to the neat polymer. The proposed composites can find application in a number of everyday products where polycarbonate is the base polymer.

Structure-property relationships in Sterculia urens/polyvinyl alcohol electrospun composite nanofibres.

Sterculia urens (Gum Karaya) based polyvinyl alcohol (PVA) composite nanofibres have been successfully electrospun after chemical modification of S. urens to increase its solubility. The effect of deacetylated S. urens (DGK) on the morphology, structure, crystallization behaviour and thermal stability was studied for spuned fibres before and after spinning post treatment. An apparent increase in the PVA crystallinity were observed in the PVA-DGK composite nanofibres indicating S. urens induced crystallization of PVA. The pure PVA nanofibre and the nanofibres of PVA-DGK composites were introduced to post electrospinning heat treatment at 150°C for 15 min. The presence of sterculia gum reduced the fibre diameter and distribution of the nanofibres due to the increased stretching of the fibres during spinning. Switching of the thermal behaviour occurs due to post spinning heat treatments.

Surfactant-induced thermomechanical and morphological changes in TiO2-polystyrene nanocomposites.

Nanocomposites of polystyrene and TiO2 colloidal nanorods with different loadings have been prepared by mixing pre-synthesized oleic acid capped colloidal TiO2 nanorods into commercial polystyrene via solvent blending using chloroform. The microstructure and morphology of the nanocomposites was evaluated by wide angle X-ray diffraction and transmission electron microscopy. The observations revealed that the surfactant plays an important role for interactions between the polymer and the filler. Differential scanning calorimetry showed that the glass transition temperature of the nanocomposites decreased which is consistent with the surfactant acting as a plasticizer in the polystyrene matrix. Thermogravimetric analysis revealed that the nanocomposites show no significant improvement in thermal stability as compared to the bare PS up to a temperature of 400 °C. However, after 400 °C, the TGA curve shifts a little to higher temperature as compared to the bare PS. The dynamic mechanical properties of the nanocomposites indicate that the storage modulus, loss modulus, and glass transition temperature do not change with increasing nanorods content of 2 and 4 wt% but decrease afterward for 8 wt%. Transmission electron microscopy images clearly show debonding characteristics in polystyrene matrix.

Adhesion and proliferation of osteoblast-like cells on anodic porous alumina substrates with different morphology.

We have fabricated nanoporous alumina surfaces by means of anodization in oxalic acid in different conditions and used them as the substrates for the growth of cells from a human osteoblast-like cell line. The rough nanoporous alumina substrates have been compared both with smooth standard Petri dishes used as the control and with commercial substrates of similar material. The viability of the cells has been assessed at different culture times of 4, 11, 18, and 25 days in vitro. It turned out that the porous side of the galvanostatically fabricated alumina performed similar to the control and better than the commercial porous alumina, whereas the potentiostatically fabricated porous alumina performed better than all the other substrates at all times, and in particular at the two shortest time periods of 4 and 11 days in vitro. The best performance of the substrates is associated with intermediate surface roughness and feature spacing.

Preparation and characterization of a BisGMA-resin dental restorative composites with glass, silica and titania fillers.

A photo-polymerizable Bisphenol-A diglycidylether methacrylate resin was characterized by Fourier transform infrared spectroscopy after its irradiation under different conditions to identify the best curing. Bonding-agent free composites with particles of ball-milled glass, silica and titania at loading of 10 and 50%wt were prepared, and their viscoelastic properties investigated by dynamic mechanical analysis, in experimental conditions close to the working environment in the mouth. All composites showed good stability at the considered conditions. The stiffest composite was the silica one, which was based on the smallest primary particles. The storage moduli close to room temperature (25°C) and mastication frequency (1 Hz) were extracted as reference bending moduli for the materials, and compared to static compressive moduli measured by nanoindentation performed by atomic force microscopy.Nanoindentation showed qualitative results in agreement with dynamic mechanical analysis as to the ranking of different materials, while resulting in approximately two-fold elastic modulus.

Fabrication of large-area ordered and reproducible nanostructures for SERS biosensor application.

We propose a large-area SERS device with efficient fluorescence quenching capability. The substrate is based on anodic porous alumina templates with various pore size and wall thickness as small as 15 and 36 nm, respectively. The nano-patterned SERS substrate, with excellent control and reproducibility of plasmon-polaritons generation, shows very efficient enhanced Raman signal in the presence of intrinsically fluorescent molecules such as cresyl violet, rhodamine, and green fluorescent protein. This work demonstrates that, when the nanostructures are properly designed and fabricated, Raman and fluorescence spectroscopy can be used in combination in order to obtain complementary molecular informations. Theoretical simulation shows excellent agreement with the experimental findings. The enhancement factor is found to be 10(3)-10(4), with respect to flat gold surface when the molecules are supposed to be closely packed, with considerable fluorescence suppression, showing a promising disposable biosensor.

Atomic force microscopy nanoindentation of a dental restorative midifill composite.

OBJECTIVES: We investigated the elastic properties of one dental restoration resin composite of common use, Venus Diamond, at submicrometer spatial resolution. METHODS: We performed both nanoindentation experiments with atomic force microscopy, and microindentation experiments with a traditional indenter setup. We also used scanning electron microscopy and energy dispersive X-rays spectroscopy to better understand the correlation between properties and microscopic structure and composition. RESULTS: With atomic force microscopy we obtained quantitative evaluation of the elastic modulus (10.8 ± 4.3 GPa), in agreement with the microindentation value (reduced modulus of 12.7 ± 2.0 GPa), and by microindentation we also obtained an hardness value (460 ± 109 MPa) compatible in turn with the nominal value provided by the material manufacturer (H ∼ 578 MPa). The nanoindentation also revealed that no relevant difference in elasticity appears between the 5 and 10 µm diameter filler particles and the surrounding areas, showing an excellent uniformity of the composite. In support of this finding, compositional uniformity of the material was also observed by X-rays spectroscopy. We conclude that the composite contains prepolymerized particles. SIGNIFICANCE: We demonstrate that, in addition to reliable quantitative analysis, the high resolution and two-dimensional mapping capability of atomic force microscopy allows for advanced insights into the microstructure of the composite that are not accessible via traditional microindentation.

Studies on Flowability, Compressibility and In-vitro Release ofTerminalia chebula Fruit Powder Tablets.

The dried fruit of Terminalia chebula is widely used for its laxative properties. The objective of the present study was to examine the flowability and compressibility of Terminalia chebula fruit powder, subsequently developing its tablet formulations by utilizing wet granulation and direct compression technology. Initial studies on flowability and compressibility revealed that the fruit powder flows poorly, is poorly compressible and mucilaginous in nature. The consolidation behaviors of the fruit powder and of its tablet formulations were studied using the Kawakita, Heckel and Leuenberger equations. Kawakita analysis revealed reduced cohesiveness hence improved flowability was achieved in formulations prepared by direct compression and the wet granulation technique. The Heckel plot showed that the Terminalia chebula fruit powder when formulated using direct compression showed initial fragmentation followed by plastic deformation and that the granules exhibited plastic deformation without initial fragmentation. The compression susceptibility parameter obtained from the Leuenberger equation for compacts formed by using the direct compression and wet granulation techniques indicated that the maximum crushing strength is reached faster and at lower compression pressures. The Tannin content (with reference to standard tannin) in fruit powder and tablet formulations was determined by UV spectrophotometry at 273 nm. The in-vitro dissolution study in simulated SGF (without enzymes) showed more than a 90% release of tannin from the tablets with in 1 h. The brittle fracture index value revealed that tablets prepared from granules showed less fracture tendency in comparison to those formed by direct compression formulation. From this study, it was concluded that the desired flowability, compressibility and compactibility of Terminalia chebula fruit powder can be obtained by using the direct compression and wet granulation techniques.

Atomic force microscopy in vitro study of surface roughness and fractal character of a dental restoration composite after air-polishing.

BACKGROUND: Surface roughness is the main factor determining bacterial adhesion, biofilm growth and plaque formation on the dental surfaces in vivo. Air-polishing of dental surfaces removes biofilm but can also damage the surface by increasing its roughness. The purpose of this study was to investigate the surface damage of different conditions of air-polishing performed in vitro on a recently introduced dental restorative composite. METHODS: Abrasive powders of sodium bicarbonate and glycine, combined at different treatment times (5, 10 and 30 s) and distances (2 and 7 mm), have been tested. The resulting root mean square roughness of the surfaces has been measured by means of atomic force microscopy, and the data have been analyzed statistically to assess the significance. Additionally, a fractal analysis of the samples surfaces has been carried out. RESULTS: The minimum surface roughening was obtained by air-polishing with glycine powder for 5 s, at either of the considered distances, which resulted in a mean roughness of ~300 nm on a 30 × 30 µm2 surface area, whereas in the other cases it was in the range of 400-750 nm. Both untreated surfaces and surfaces treated with the maximum roughening conditions exhibited a fractal character, with comparable dimension in the 2.4-2.7 range, whereas this was not the case for the surfaces treated with the minimum roughening conditions. CONCLUSIONS: For the dental practitioner it is of interest to learn that use of glycine in air polishing generates the least surface roughening on the considered restorative material, and thus is expected to provide the lowest rate of bacterial biofilm growth and dental plaque formation. Furthermore, the least roughening behaviour identified has been correlated with the disappearance of the surface fractal character, which could represent an integrative method for screening the air polishing treatment efficacy.

Local increase in stiffness of agarose gel layer by patterning with polylysine measured via atomic force microscopy.

Films of agarose gel impregnated with polylysine spotted from an aqueous solution have been characterized by atomic force microscopy performed in deionized water. An increase in contact stiffness of the composite substrate on the spotted areas has been observed, for increasing polylysine concentration. For the considered agarose layer thickness of approximately 0.9 microm when dry, the polylysine concentration threshold for stiffening is as low as approximately 0.1 mg/mL. Above this threshold the stiffening coefficient increases slightly with concentration in the considered range (up to 0.7 mg/mL), reaching a highest value of approximately 2.3. For concentrations >or=0.3 mg/mL the stiffening at the polylysine spots was also accompanied by a locally lower film thickness. For accurate quantification of the stiffness, representative force-distance curves extracted from the respective regions of interest (spots and agarose substrate off the spots) have been processed. The Hertz model of purely elastic tip-surface interaction has been adopted, with appropriate hypothesis on both tip shape and optimum indentation depth. The resulting Young's moduli of the agarose layer and of the polylysine spots are approximately 45 kPa and approximately 95 kPa, respectively, with an estimated uncertainty of approximately 15%.

AFM measurement of the stiffness of layers of agarose gel patterned with polylysine.

Films of agarose gel microspotted with polylysine aqueous solution have been characterized by atomic force microscopy carried out in deionized water. Thickness and surface morphology of the layers have been checked, and the effect of polylysine impregnation on the local elasticity has been investigated. An increase in contact stiffness of the organic layer at the spotted areas has been observed, correlated with the polylysine concentration. For the considered agarose layer thickness of ~0.9 µm in dry condition, the concentration threshold at which stiffening appears is ~0.1 mg/mL. Above this threshold, the stiffening coefficient becomes approximately twofold and seems not to increase significantly with concentration in the range 0.3-0.7 mg/mL. For concentrations above the stiffening threshold, this effect is also accompanied by a locally lower film thickness. For quantitative determination of the stiffness, force-distance curves extracted from the regions of interest of spots and agarose substrate have been selected and processed. These curves were fitted to the Hertz model of purely elastic tip-surface interaction, under appropriate assumptions on both tip shape and optimum indentation depth. In this way, we could determine the Young's modulus of the agarose layer to be ~50 kPa and quantitatively confirm the stiffening due to polylysine.

Use of ionic liquid in fabrication, characterization, and processing of anodic porous alumina.

Two different ionic liquids have been tested in the electrochemical fabrication of anodic porous alumina in an aqueous solution of oxalic acid. It was found that during galvanostatic anodization of the aluminum at a current density of 200 mA/cm2, addition of 0.5% relative volume concentration of 1-butyl-3-methylimidazolium tetrafluoborate resulted in a three-fold increase of the growth rate, as compared to the bare acidic solution with the same acid concentration. This ionic liquid was also used successfully for an assessment of the wettability of the outer surface of the alumina, by means of liquid contact angle measurements. The results have been discussed and interpreted with the aid of atomic force microscopy. The observed wetting property allowed to use the ionic liquid for protection of the pores during a test removal of the oxide barrier layer.