S.M. Mirabedini

PMMA-grafted nanoclay as novel filler for dental adhesives

OBJECTIVE The aim of this study was to investigate the benefits of incorporation of poly(methyl methacrylate)-grafted-nanoclay on the bond strength of an experimental one-bottle dentin bonding system. The effect of the modification on the stability of the nanoparticle dispersion in the dilute adhesive was also studied. MATERIALS AND METHODS Poly(methyl methacrylate) was grafted onto the pristine Na-MMT nanoclay (Cloisite Na(+)) through the free radical polymerization of methyl methacrylate in an aqueous media in the presence of ammonium persulfate as initiator. A reactive surfactant (AMPS) was also used in the reaction recipe to provide active sites on the surface of the nanoclay. The grafting polymerization reaction was carried out at 70 degrees C. The PMMA-g-nanoclay was then coagulated in methanol and filtered. The resulting PMMA-g-nanoclay was characterized using FTIR, TGA, X-ray diffraction (XRD) and particle size distribution analysis. The modified nanoclay was added to an experimental dentin bonding system as filler and the morphology of the nanoclay layers in the adhesive matrix was studied using TEM and XRD. Shear bond strength of the adhesives containing different filler contents was tested on the caries-free extracted human premolar teeth. The mode of failure was studied by scanning electron microscopy. The stability of the nanoclay dispersion in the dilute adhesive was also studied using a separation analyzer. The results were then statistically analyzed and compared. RESULTS The grafting of poly(methylmethacrylate) onto the nanoclay was confirmed and the results revealed a partially exfoliated structure for the PMMA-g-nanoclay. Incorporation of the modified nanoclay provided a dentin bonding system with higher shear bond strength. The dispersion stability of the modified nanoparticles in the dilute adhesive was also increased more than 40 times in comparison with the pristine nanoclay. SIGNIFICANCE The grafting modification provided nanoclay particles with higher dispersion stability than pristine Na-MMT nanoclay in a dilute dentin bonding system. Incorporation of the modified nanoclay into the bonding system provided higher shear bond strength. The finding would be beneficial in producing nano-filler containing adhesive systems.

Investigating the role of surface treated titanium dioxide nanoparticles on self-cleaning behavior of an acrylic facade coating

In this study, the addition of silane treated TiO2 nanoparticles on the self-cleaning properties of an acrylic facade coating was evaluated. Tetraethoxyorthosilicate, TEOS, was used for surface treatment of TiO2 nanoparticles. The silica grafting on the TiO2 nanoparticles was characterized via Fourier Transform Infrared spectroscopy, specific surface area measurement, pore size distribution, and real density measurements. The effect of surface treatment and content of nanoparticles on the photocatalytic activity of acrylic coating and self-cleaning properties was studied. For this purpose, the photodegradation of Rhodamine B (Rh.B) dyestuff, as a colorant model, was investigated by colorimetric technique, while the coating samples were exposed to UVA irradiation. Performance of the acrylic coating films was evaluated by gloss change during accelerated weathering conditions. Also, the surface morphology of the coating films was studied using SEM analysis. The results showed that the addition of both treated and untreated TiO2 nanoparticles provides self-cleaning property to the acrylic coatings. However, silica surface treatment of TiO2 nanoparticles reduces the coating degradation caused by TiO2. This is more evident when higher concentrations of the treated TiO2 nanoparticles are used.

Investigating changes in electrochemical properties when nano-silica is incorporated into an acrylic-based polyurethane clearcoat

Two different types of nano-silica (i.e., hydrophilic Aerosil 200 and hydrophobic Aerosil R805) were employed in the preparation of 2-pack acrylic polyol polyurethane nano-coatings so that the electrochemical properties of the resultant coatings could be investigated. Electrochemical impedance spectroscopy was used to evaluate the corrosion performances of such nano-coatings applied onto mild steel substrates that were immersed in 3.5% (w/w) NaCl solutions. It was observed coatings that contained nano-silica increased the barrier properties of the binder, as well as the coatings’ electrochemical resistance compared with pure polyurethane coatings. The surface tension of pure polyurethane was measured by a tensiometer. Rheological properties were also determined at various shear rates by a rotaviscometer. Results showed that the surface tension of hydrophobic nano-silica is very close to the pure polyurethane matrix, giving the better compatibility of the two. This was further confirmed by transmission electron microscopy and by the fact that the hydrophobically filled nano-silica coatings showed shear thinning behavior in the fluid state. Also observed was better corrosion performance of the resultant hydrophobic nano-coatings compared to coatings embedded with hydrophilic nano-silica.