Structure of disordered gold-polymer thin films using small angle x-ray scattering

We have investigated the structure of disordered gold-polymer thin films using small angle x-ray scattering and compared the results with the predictions of a theoretical model based on two approaches-a structure form factor approach and the generalized Porod law. The films are formed of polymer-embedded gold nanoclusters and were fabricated by very low energy gold ion implantation into polymethylmethacrylate (PMMA). The composite films span (with dose variation) the transition from electrically insulating to electrically conducting regimes, a range of interest fundamentally and technologically. We find excellent agreement with theory and show that the PMMA-Au films have monodispersive or polydispersive characteristics depending on the implanted ion dose. (C) 2010 American Institute of Physics. [doi:10.1063/1.3493241]

Pseudomonas fluorescens lipase immobilization on polysiloxane-polyvinyl alcohol composite chemically modified with epichlorohydrin

The technique based on sol-gel approach was used to generate silica matrices derivatives by hydrolysis of silane compounds. The present work evaluates a hybrid matrix obtained with tetraethoxysilane (TEOS) and polyvinyl alcohol (PVA) on the immobilization yield of lipase from Pseudomonas fluorescens. The resulting polysiloxane-polyvinyl alcohol (POS-PVA) matrix combines the property of PVA as a suitable polymer to retain proteins with an excellent optical, thermal and chemical stability of the host silicon oxide matrix. Aiming to render adequate functional groups to the covalent binding with the enzyme the POS-PVA matrix was chemically modified using epichlorohydrin. The results were compared with immobilized derivative on POS-PVA activated with glutaraldehyde. Immobilization yield based on the recovered lipase activity depended on the activating agent and the highest efficiency (32%) was attained when lipase was immobilized on POS-PVA activated with epichlorohydrin, which, probably, provided more linkage points for the covalent bind of the enzyme on the support. This was confirmed by determining the morphological properties using different techniques as X-ray diffraction and scanning electron microscopy (SEM). Comparative studies were carried out to attain optimal activities for free lipase and immobilized systems. For this purpose, a central composite experimental design with different combinations of pH and temperature was performed. Enzymatic hydrolysis with the immobilized enzyme in the framework of the Michaelis-Menten mechanism was also reported. Under optimum conditions, the immobilized derivative on POS-PVA activated with epichlorohydrin showed to have more affinity for the substrate in the hydrolysis of olive oil, with a Michaelis-Menten constant value (K-m) of 293 mM, compared to the value of 401 mM obtained for the immobilized lipase on support activated with glutaraldehyde. Data generated by DSC showed that both immobilized derivatives have similar thermal stabilities. (C) 2007 Elsevier B.V. All rights reserved.

Composite materials obtained from textile fiber residue

This article presents the use of fibers residue from textile industry to minimize environmental problems associated with material accumulation. Composite materials utilizing textile fiber residues and high density polyethylene were prepared. Effect of treatment with hot water on fibers to prepare composites was studied to provide an improvement in mechanical properties of these materials. This treatment on fibers was evaluated by X-ray diffraction and scanning electron microscopy techniques. Experimental results of mechanical properties indicated higher mechanical strength for treated fiber composites compared to the untreated fiber composites.

Thermal, structural and optical properties of Al(2)CoO(4)-Crocoite composite nanoparticles used as pigments

Al(2)CoO(4)-PbCrO(4) and Al(2)CoO(4)-Pb(2)CrO(5) crystalline powders in different proportions were obtained by the polymeric precursor method. Differential scanning calorimetry (DSC) and thermogravimetry (TG) techniques were used to accurately characterize the distinct thermal events occurring during synthesis. The TG and DSC results revealed a series of overlapping decomposition reactions due to different exothermal events, which were identified as H(2)O and NO(x) elimination and polymer pyrolysis. The X-ray diffraction patterns of the xAl(2)CoO(4)-(1 - x)PbCrO(4) and xAl(2)CoO(4)-(1 - x)Pb(2)CrO(5) mixed compounds, with x = 1, 0.75, 0.5, 0.25 and 0, were obtained in the crystalline form with their respective phases, and proved consistent with the nominal compositions. The synthesis of these two systems yielded nine different colors and shades.

Bond strength and transversal deformation aging on cement-polymer adhesive mortar

Polymer-modified mortar is widely used to set ceramic tiles used as external finishing for high rise buildings in countries such as Brazil, Israel, Singapore and Portugal, mainly because it shows better bond strength and flexibility as compared to the traditional ones. Despite this, the results in the literature already published concerning the long-term performance of those composite mortars are is not conclusive. This paper, based on a laboratory program, compared the performance over time of four commercial polymer-modified adhesive mortars exposed to a typical Brazilian outdoor aging environment and to an indoor environment in terms of mortar flexibility and the bond strength to porcelain tiles. The results show that under laboratory condition, the mortars are more flexible and have higher bond strength than under external condition, and that there is an important correlation between the transversal deformability and the bond strength. (C) 2008 Elsevier Ltd. All rights reserved.

Composite pre-heating: Effects on marginal adaptation, degree of conversion and mechanical properties

Objectives. This study evaluated the effect of composite pre-polymerization temperature and energy density on the marginal adaptation (MA), degree of conversion (DC), flexural strength (FS), and polymer cross-linking (PCL) of a resin composite (Filtek Z350, 3M/ESPE). Methods. For MA, class V cavities (4mmx2mmx2mm) were prepared in 40 bovine incisors. The adhesive system Adper Single Bond 2 (3M/ESPE) was applied. Before being placed in the cavities, the resin composite was either kept at room-temperature (25 degrees C) or previously pre-heated to 68 degrees C in the Calset (TM) device (AdDent Inc., Danbury, CT, USA). The composite was then light polymerized for 20 or 40s at 600mW/cm(2) (12 or 24 J/cm(2), respectively). The percentage of gaps was analyzed by scanning electron microscopy, after sectioning the restorations and preparing epoxy resin replicas. DC (n = 3) was obtained by FT-Raman spectroscopy on irradiated and non-irradiated composite surfaces. FS (n = 10) was measured by the three-point-bending test. KHN (n = 6) was measured after 24h dry storage and again after immersion in 100% ethanol solution for 24 h, to calculate PCL density. Data were analyzed by appropriate statistical analyses. Results. The pre-heated composite showed better MA than the room-temperature groups. A higher number of gaps were observed in the room-temperature groups, irrespective of the energy density, mainly in the axial wall (p < 0.05). Composite pre-heating and energy density did not affect the DC, FS and PCL (p > 0.05). Significance. Pre-heating the composite prior to light polymerization similar in a clinical situation did not alter the mechanical properties and monomer conversion of the composite, but provided enhanced composite adaptation to cavity walls. (C) 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Influence of curing rate on softening in ethanol, degree of conversion, and wear of resin composite

Purpose: To investigate the effect of curing rate on softening in ethanol, degree of conversion, and wear of resin composites. Methods: With a given energy density and for each of two different light-curing units (QTH or LED), the curing rate was reduced by modulating the curing mode. Thus, the irradiation of resin composite specimens (Filtek Z250, Tetric Ceram, Esthet-X) was performed in a continuous curing mode and in a pulse-delay curing mode. Wallace hardness was used to determine the softening of resin composite after storage in ethanol. Degree of conversion was determined by infrared spectroscopy (FTIR). Wear was assessed by a three-body test. Data were submitted to Levene`s test, one and three-way ANOVA, and Tukey HSD test (alpha= 0.05). Results: Immersion in ethanol, curing mode, and material all had significant effects on Wallace hardness. After ethanol storage, resin composites exposed to the pulse-delay curing mode were softer than resin composites exposed to continuous cure (P< 0.0001). Tetric Ceram was the softest material followed by Esthet-X and Filtek Z250 (P< 0.001). Only the restorative material had a significant effect on degree of conversion (P< 0.001): Esthet-X had the lowest degree of conversion followed by Filtek Z250 and Tetric Ceram. Curing mode (P= 0.007) and material (P< 0.001) had significant effect on wear. Higher wear resulted from the pulse-delay curing mode when compared to continuous curing, and Filtek Z250 showed the lowest wear followed by Esthet-X and Tetric Ceram. (Am J Dent 2011;24:115-118).

Bone cell responses to the composite of Ricinus communis polyurethane and alkaline phosphatase

The aim of this study was to evaluate the response of osteoblastic cells to the composite of Ricinus cominunis polyurethane (RCP) and alkaline phosphatase (ALP) incubated in synthetic body fluid (SBF). RCP pure (RCPp) and RCP blended with ALP 6 mg/mL polymer (RCP+ALP) were incubated in SBF for 17 days. Four groups of RCP were tested: RCPp, RCP+ALP, and RCPp and RCP+ALP incubated in SBF (RCPp/SBF and RCP+ALP/SBF). Stem cells from rat bone marrow were cultured in conditions that allowed osteoblastic differentiation on RCP discs and were evaluated: cell adhesion, culture growth, cell viability, total protein content, ALP activity, and bone-like nodule formation. Data were compared by ANOVA or Kruskal-Wallis test. The group RCP-A P was highly cytotoxic and, therefore, was not considered here. Cell adhesion (p = 0.14), culture growth (p = 0.39), viability (p = 0.46) and total protein content (p = 0.12) were not affected by either RCP composition or incubation in SBE ALP activity was affected (p = 0.0001) as follows: RCPp < RCPp/SBF < RCP+ALP/SBF. Bone-like nodule formation was not observed on all evaluated groups. The composite RCP+ALP prior to SBF incubation is cytotoxic and must not be considered as biomaterial, but the incorporation of ALP to the RCP followed by SBF incubation could be a useful alternative to improve the biological properties of the RCP. (c) 2007 Wiley Periodicals, Inc.

Electrical, optical, and structural studies of shallow-buried Au-polymethylmethacrylate composite films formed by very low energy ion implantation

The authors present here a summary of their investigations of ultrathin films formed by gold nanoclusters embedded in polymethylmethacrylate polymer. The clusters are formed from the self-organization of subplantated gold ions in the polymer. The source of the low energy ion stream used for the subplantation is a unidirectionally drifting gold plasma created by a magnetically filtered vacuum arc plasma gun. The material properties change according to subplantation dose, including nanocluster sizes and agglomeration state and, consequently also the material electrical behavior and optical activity. They have investigated the composite experimentally and by computer simulation in order to better understand the self-organization and the properties of the material. They present here the results of conductivity measurements and percolation behavior, dynamic TRIM simulations, surface plasmon resonance activity, transmission electron microscopy, small angle x-ray scattering, atomic force microscopy, and scanning tunneling microscopy. (C) 2010 American Vacuum Society [DOI: 10.1116/1.3357287]

Continuous and gradual photo-activation methods: influence on degree of conversion and crosslink density of composite resins

Thermal properties and degree of conversion (DC%) of two composite resins (microhybrid and nanocomposite) and two photo-activation methods (continuous and gradual) displayed by the light-emitting diode (LED) light-curing units (LCUs) were investigated in this study. Differential scanning calorimetry (DSC) thermal analysis technique was used to investigate the glass transition temperature (T(g)) and degradation temperature. The DC% was determined by Fourier transform infrared spectroscopy (FT-IR). The results showed that the microhybrid composite resin presented the highest T(g) and degradation temperature values, i.e., the best thermal stability. Gradual photo-activation methods showed higher or similar T(g) and degradation temperature values when compared to continuous method. The Elipar Freelight 2 (TM) LCU showed the lowest T(g) values. With respect to the DC%, the photo-activation method did not influence the final conversion of composite resins. However, Elipar Freelight 2 (TM) LCU and microhybrid resin showed the lowest DC% values. Thus, the presented results suggest that gradual method photo-activation with LED LCUs provides adequate degree of conversion without promoting changes in the polymer chain of composite resins. However, the thermal properties and final conversion of composite resins can be influenced by the kind of composite resin and LCU.

Influence of light guide tip used in the photo-activation on degree of conversion and hardness of one nanofilled dental composite

The aim of this study was to evaluate the degree of conversion and hardness of a dental composite resin Filtek (TM) Z-350 (3M ESPE, Dental Products St. Paul, MN) photo-activated for 20 s of irradiation time with two different light guide tips, metal and polymer, coupled on blue LED Ultraled LCU (Dabi Atlante, SP, Brazil). With the metal light tip, power density was of 352 and with the polymer was of 456 mW/cm(2), respectively. Five samples (4 mm in diameter and 2mm in thickness-ISO 4049), were made for each Group evaluated. The measurements for DC (%) were made in a Nexus-470 FT-IR, Thermo Nicolet, E.U.A. Spectroscopy (FTIR). Spectra for both uncured and cured samples were analyzed using an accessory of reflectance diffuse. The measurements were recorded in absorbance operating under the following conditions: 32 scans, 4 cm(-1) resolution, 300-4000 cm(-1) wavelength. The percentage of unreacted carbon double bonds (% C=C) was determined from the ratio of absorbance intensities of aliphatic C=C (peak at 1637 cm(-1)) against internal standard before and after curing of the sample: aromatic C-C (peak at 1610 cm(-1)). The Vickers hardness measurements (top and bottom surfaces) were performed in a universal testing machine (Buehler MMT-3 digital microhardness tester Lake Bluff, Illinois USA). A 50 gf load was used and the indenter with a dwell time of 30 s. The data were submitted to the test t Student at significance level of 5%. The mean values of degree of conversion for the polymer and metal light guide tip no were statistically different (p = 0.8389). The hardness mean values were no statistically significant different among the light guide tips (p = 0.6244), however, there was difference between top and bottom surfaces (p < 0.001). The results show that so much the polymer light tip as the metal light tip can be used for the photo-activation, probably for the low quality of the light guide tip metal.

Evidence of redox interactions between polypyrrole and Fe(3)O(4) in polypyrrole-Fe(3)O(4) composite films

The electrical properties of conducting polymers make them useful materials in a wide number of technological applications. In the last decade, an important effect on the properties of the conducting polymer when iron oxides particles are incorporated into the conductive matrix was shown. In the present study, films of polypyrrole were synthesized in the presence of magnetite particles. The effect of the magnetite particles on the structure of the polymer matrix was determined using Raman spectroscopy. Mass variations at different concentrations of Fe(3)O(4) incorporated into the conducting matrix were also measured by means of quartz crystal microbalance. Additionally, the changes in the resistance of the films were evaluated over time by electrochemical impedance spectroscopy in solid state. These results show that the magnetite incorporation decreases polymeric film resistance and Raman experiments have evidenced that the incorporation of magnetite into polymeric matrix not only stabilizes the polaronic form of the polypyrrole, but also preserves the polymer from further oxidation. (C) 2009 Elsevier Ltd. All rights reserved.

Micro/nanostructured carbon composite modified with a hybrid redox mediator and enzymes as a glucose biosensor

A carbon micro/nanostructured composite based on cup-stacked carbon nanotubes (CSCNTs) grown onto a carbon felt has been found to be an efficient matrix for enzyme immobilization and chemical signal transduction. The obtained CSCNT/felt was modified with a copper hexacyanoferrate/polypyrrole (CuHCNFe/Ppy) hybrid mediator, and the resulting composite electrode was applied to H(2)O(2) detection, achieving a sensitivity of 194 +/- 15 mu A mmol(-1) L. The results showed that the CSCNT/felt matrix significantly increased the sensitivity of CuHCNFe/Ppy-based sensors compared to those prepared on a felt unrecovered by CSCNTs. Our data revealed that the improved sensitivity of the as-prepared CuHCNFe/Ppy-CSCNT/felt composite electrode can be attributed to the electronic interactions taking place among the CuHCNFe nanocrystals, Ppy layer and CSCNTs. In addition, the presence of CSCNTs also seemed to favor the dispersion of CuHCNFe nanocrystals over the Ppy matrix, even though the CSCNTs were buried under the conducting polymer layer. The CSCNT/felt matrix also enabled the preparation of a glucose biosensor whose sensitivity could be tuned as a function of the number of glucose oxidase (GOx) layers deposited through a Layer-by-Layer technique with an sensitivity of 11 +/- 2 mu A mmol(-1) L achieved at 15 poly(diallyldimethylammoniumchloride)/GOx bilayers. (C) 2011 Elsevier Ltd. All rights reserved.

Thermoset matrix reinforced with sisal fibers: Effect of the cure cycle on the properties of the biobased composite

Thermoset phenolic composites reinforced with sisal fibers were prepared to optimize the cure step. In the present study, processing parameters such as pressure, temperature, and time interval were varied to control the vaporization of the water generated as a byproduct during the crosslinking reaction. These molecules can vaporize forming voids, which in turn affect the final material properties. The set of results on impact strength revealed that the application of higher pressure before the gel point of the phenolic matrix produced composites with better properties. The SEM images showed that the cure cycle corresponding to the application of higher values of molding pressure at the gel point of the phenolic resin led to the reduction of voids in the matrix. In addition, the increase in the molding pressure during the cure step increased the resin interdiffusion. Better filling of the fiber channels decreased the possibility of water molecules diffusing through the internal spaces of the fibers. These molecules then diffused mainly through the bulk of the thermoset matrix, which led to a decrease in the water diffusion coefficient (D) at all three temperatures (25, 55 and 70 degrees C) considered in the experiments. (C) 2009 Elsevier Ltd. All rights reserved.

Fracture resistance of weakened roots restored with composite resin and glass fiber post

This study evaluated the fracture resistance of weakened roots restored with glass fiber posts, composite resin cores and complete metal crowns. Thirty maxillary canines were randomly divided into 3 groups of 10 teeth each: teeth without weakened roots (control); teeth with partially weakened roots (PWR) and teeth with and largely weakened roots (LWR). The control group was restored with glass fiber posts and a composite resin core. Teeth in the PWR and LWR groups were flared internally to standardized dimensions in order to simulate root weakness. Thereafter, the roots were partially filled with composite resin and restored in the same way as in the control group. The specimens were exposed to 250,000 cycles in a controlled chewing simulator. All intact specimens were subjected to a static load (N) in a universal testing machine at 45 degrees to the long axis of the tooth until failure. Data were analyzed by one-way ANOVA and Dunnett's test for multiple comparisons (p=0.05). There were statistically significant difference differences (p<0.01) among the groups (control group = 566.73 N; PWR = 409.64 N; and LWR = 410.91 N), with significantly higher fracture strength for the control group. There was no statistically significant difference (p>0.05) between the weakened groups. The results of this study showed that thicker root dentin walls significantly increase the fracture resistance of endodontically treated teeth.