Selda Keskin

Effect of Au and Au@Ag core–shell nanoparticles on the SERS of bridging organic molecules

Gold nanoparticles (AuNPs) with about 6 nm size were produced and stabilized with mercaptopropionic acid (MPA) film to produce a monolayer protected cluster (MPC) of AuS(CH(2))(2)COOH. 4-Aminothiophenol (ATP) molecules were introduced to the activated carboxylic acid ends of the film surrounding the AuNPs to produce AuS(CH(2))(2)CONHPhSH MPC. These modified AuNPs were again self-assembled with Au@Ag core-shell bimetallic nanoparticles via the -SH groups to produce an organic bridge between Au and Au@Ag metallic nanoparticles. An unusually strong enhancement of the Raman signals was observed and assigned to the plasmon coupling between the AuNPs and Au@Ag NPs bridged assembly. Formation of AuS(CH(2))(2)COOH and AuS(CH(2))(2)CONHPhSH clusters and AuS(CH(2))(2)CONHPhS(Au@Ag) assembly is confirmed by UV-Vis, reflection-absorption IR spectroscopy (RAIRS) and X-ray photoelectron spectroscopy (XPS), as well as by TEM analysis. The SERS activity of the AuNPs and Au@Ag NPs was tested using the HS(CH(2))(2)CONHPhSH molecule as a probe to compare the effectiveness of monometallic and bimetallic systems. SERS spectra show that Au@Ag bimetallic nanoparticles are very effective SERS-active substrates.

Preparation and Characterization of Neodymia Doped PVA/Zr-Ce Oxide Nanocrystalline Composites via Electrospinning Technique

In this study, neodymia doped poly(vinyl) alcohol/zirconium–cerium acetate (PVA/Zr-Ce) nanofibers were prepared using the electrospinning technique, and then calcined at 800°C for 2 hours. For this purpose, PVA/Zr-Ce polymer solutions doped with different concentrations of neodymia were prepared using electrospinning technique, and then calcined and sintered at 800°C for 2 hours. The effect of neodymia doping was investigated in terms of solution properties, morphological changes and thermal characteristics. The fibers were characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), and scanning electron microscope (SEM). The measurements showed that the conductivity, pH, viscosity, and surface tension of the hybrid polymer solutions have decreased with increasing Nd acetate content. The FT-IR spectra of the fibers were in good accordance with the literature. The average crystal size values for calcined and sintered samples which were obtained from precursor solutions were calculated. XRD analysis showed that the crystallite size was decreased with increasing Nd content. This result is verified by the calculation of the total areas of the peaks appeared in the XRD spectra. The very sharp and high intense peaks found in the diffraction patterns revealed the crystalline nature of the product. Moreover, the SEM micrograph of the fibers showed that the average fiber diameters decreased with increasing Nd content.

Evaluation of Laser Treatment on Reline-Base Composites

The effects of different laser treatments on some mechanical properties of acrylic resin and soft liner were investigated. A total of 60 test specimens were fabricated according to test requirements. The specimens were roughened with Potassium-ticanyl-Phosphate (KTP), Er:YAG, and Nd:YAG lasers before application of soft liner. The flexural, peel, and tensile bond strengths were measured using a universal testing machine. Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) spectra of surfaces were also obtained to evaluate changes on the lased surfaces. No significant difference was apparent between the tensile bond strength values of the groups. Although peel strength values obtained for each of the laser types were lower than those of the control group, flexural strength values were higher than those of the control specimens. The spectra of specimens showed that lasing led to some chemical changes on the resin surfaces. Physical changes on the treated surfaces were visualized by scanning electron microscopy (SEM) analysis. Results of this study suggest that such treatments may be warranted because of the increase in flexural strength.

Peel bond strength of two silicone soft liners to a heat-cured denture base resin.

PURPOSE This study investigated the peel strength of two different soft liners to a polymethylmethacrylate (PMMA) denture base resin before and after thermocycling. MATERIALS AND METHODS The silicone-based soft liner materials tested were Molloplast B and Permaflex; the denture base material was a heat-cured acrylic resin, Meliodent. A total of 40 specimens was prepared using rectangular molds with dimensions of 100 x 10 x 2 mm for PMMA and 150 x 10 x 2 mm for soft liners, as described in ASTM-D903-93. For each of the liner materials, 10 specimens were packed against a cured PMMA denture base surface as recommended by the manufacturers. The other 10 specimens were packed against PMMA denture base dough and processed together. In each group, 5 of the specimens were tested directly, while the other 5 were thermocycled in a water bath (5°C to 55°C; 3000 cycles) before testing. Peel testing was performed using an Instron testing machine. RESULTS The results revealed that peel strength values of the Permaflex specimens prepared according to the manufacturers recommendations were significantly higher than those of Molloplast B (p < 0.05). However, when packing was done against uncured PMMA dough, the difference between the specimens of two liners was not significant. Thermocycling led to significant decreases in the peel strength of both Permaflex liner specimens packed against cured/uncured PMMA resin surfaces (p < 0.05), whereas this process did not affect the strength of Molloplast B specimens. CONCLUSION Results indicated that the material Molloplast B was superior to the material Permaflex in terms of peel strength when the specimens were simultaneously polymerized with PMMA and thermocycled.

Thermal Degradation of Poly(Allyl Methacrylate) by Mass Spectroscopy and TGA

Allyl methacrylate, AMA was polymerized in CCl4 solution by α,α′‐azoisobutyronitrile at 50°C. The thermal degradation mechanism of PAMA was characterized by MS, TGA‐FT‐IR and FT‐IR‐ATR methods. The mass spectrum and TGA thermogram showed two stage degradation. The first stage of degradation was mostly linkage type degradation for the fragmentation of pendant allyl groups at 225–350°C. In the second stage, at 395–515°C, the degradation is random scission and depolymerization types. This was also supported by direct thermal pyrolysis of polymer under vacuum. The degradation fragments of MS and TGA were in agreement. In the degradation process, monomer degraded further to CO, CO2, allyl and ether groups. No strong monomer peak was observed in mass spectrum.

Flexural and Bonding Properties of a Denture Base Polymer Treated with Nitric Acid or Ultraviolet Radiation Before Relining with Molloplast-B

This study investigated adhesive forces and flexural strength of acrylic resin denture base relined with Molloplast-B soft lining material. To increase bonding between the two materials, the surface of the resin was modified with ultraviolet (UV) irradiation or nitric acid treatment. The peel strength greatly increased with nitric acid treatment because of the high polarity on the poly (methyl methacrylate) (PMMA) surface and the increase in the surface roughness, whereas low peel strength was seen with the UV treatment of the PMMA surface. Although both types of the surface pretreatment increased the flexural strength of PMMA-reline composites compared with the control and bulk PMMA groups, the increase in the UV-treated group was found to be higher than that of the nitric acid–treated group.

Effect of maleic anhydride pretreatment on tensile bond strength of a silicone soft liner to a denture base polymer.

PURPOSE To determine the effect of resin surface treatment with dissolved maleic anhydride in butanone added into primer on the tensile bond strength between an acrylic denture base resin and a silicone soft liner. MATERIALS AND METHODS To test tensile bond strength, standard dumbbell-shaped acrylic specimens were prepared. Five experimental groups, including the control, were tested (n = 5). Maleic anhydride solutions prepared in butanone at concentrations of 1%, 5%, 10% or 20% were then mixed with 1 ml of Primo adhesive and the mixtures were applied onto the resin bonding surfaces. Silicone liner material was applied to resin surfaces in the conventional manner. Tensile bond strength of the specimens was measured in a universal testing machine. Fractured surfaces were observed under the scanning electron microscope, and resulting chemical changes with the solutions used were analyzed spectroscopically. RESULTS The highest bond strength value was obtained for the group treated with 5% maleic anhydride (2.53 ± 0.48 MPa); the lowest value was for the group treated with 20% maleic anhydride (1.59 ± 0.29 MPa). Mixed failure was the dominant type seen in the experimental groups. Spectroscopic analysis showed the interaction of the anhydride carbonyl groups with the Primo primer. CONCLUSION The treatment of resin surfaces with maleic anhydride added to Primo adhesive effectively increased bond strength between silicone soft liner and denture base resin.

Bond Strength of a Silicone Soft Lining Material to Poly(methyl methacrylate) Resin Treated with Maleic Anhydride and its Terpolymers

This study investigated the effectiveness of surface treatment of Poly (methyl methacrylate) (PMMA) denture base resin on tensile bond strength between PMMA/silicone-based soft liner. A total of 25 specimens were fabricated and assigned into five groups (n = 5). The surfaces of PMMA were treated with maleic anhydride, maleic anhydride-styrene-vinyl-acetate, n-butylmaleate-styrene-vinyl-acetate, or n-pentamaleate-styrene-vinyl-acetate prior to Primo adhesive primer application and silicone liner placement. The Primo adhesive primer on applied group untreated dentuse base resin served as control. The tensile test was performed using a universal testing machine. Fractured surfaces were observed under Scanning Electron Microscopy (SEM) and spectroscopic interpretation of the interfaces was done by Fourier Transform Infrared (FTIR). Test results showed that surface treatment increased interfacial strength giving the highest value for n-butylmaleate-styrene-vinyl acetate treated group. SEM micrographs revealed that the specimens with n-butylmaleate-styrene-vinyl-acetate and n-penta maleate-styrene-vinyl-acetate terpolymers underwent cohesive failure. FTIR analysis indicated secondary interactions such as hydrogen bonding, possibly on acrylic resin surfaces, caused by the use of maleic anhydride and its terpolymers, and the adhesive.

Effects of some methacrylate monomers used as liquid component on tensile and flexural strengths of poly(methylmethacrylate) denture base resin

Abstract The present study was conducted to observe the effect of different monomers on tensile and flexural strengths of poly(methyl methacrylate) (PMMA) denture base resin when they were used as a liquid component. A conventional heat cured denture base polymer powder was mixed with ethyl, isobutyl and tert-butyl methacrylate monomers respectively. After the polymerisation process was completed, the tensile and flexural strengths of these specimens were compared with those of PMMA resin specimens polymerised with methylmethacrylate monomer (MMA). Tensile specimens were prepared in a dumbbell shape using a stainless steel mould constructed according to ASTM D638M-91a. Rectangular flexural specimens were prepared as designated in ASTM D790M-92. Each group was subjected to tensile strength and flexural strength tests using a universal testing machine at a crosshead speed of 50 mm min−1. In addition to mechanical tests, the structural change in the acrylic resin specimens prepared with different monomers was observed using a Fourier transform infrared spectrometer with attenuated total reflectance unit. The differences in the tensile strengths of all specimens were not found to be statistically significant (p>0·05), whereas the flexural strengths showed statistical differences among the groups tested (p<0·05). In the results of the tests performed, it was reached that the flexural and tensile strengths of acrylic resins obtained by various methacrylate monomers were different. It can be said that these acrylic resins can be used for various aims in different fields and in the dentistry field.

The Effect of Surface Treatments on Tensile Bond Strength between a Silicone Soft Liner and a Heat-Cured Denture Base Resin

This study evaluated tensile bond strength of a denture soft lining material to a poly (methylmethacrylate) (PMMA) denture base resin subjected to different surface treatment modalities and thermocycling. The materials tested were a silicone-based liner, Molloplast B®, and a heat-cured denture base resin, MeliodentTM. The denture soft lining material was packed against cured PMMA base resin, which was smoothed; sandblasted with 250-μm Al2O3 particles; or lased with a KTP laser; or against uncured PMMA dough (n = 10). In each group, five specimens were thermocycled in a water bath (5–55°C; 3000 cycles) before testing, whereas the other five were directly tested after 24 h. A tensile test was performed using a universal testing machine. Data showed that different treatment modalities of resin surfaces affected adhesion between these two materials and the highest bond values were recorded for cured/smoothed samples under each condition tested. Thermocycling of specimens had no significant reducing effect on measured bond strength values.