The organoclay/poly(methyl methacrylate) (PMMA) nanocomposites were prepared by in situ photopolymerization method using two solvents, ethanol and acetonitrile. The influences of organoclay loading, solvent nature and length of attached surfactant (C8 or C16) on thermal and mechanical properties were studied by thermogravimetric analysis and dynamic mechanical analysis. Alkylammonium surfactants with C8 and C16 chain lengths were evaluated as clay modifiers. All the nanocomposites prepared in acetonitrile exhibited improvement in their thermal stability, mainly due to the interaction between the clay and the polymer which is maximized by the exfoliated clay structure. In the case of PMMA and nanocomposites synthesized in ethanol, the thermal stability of polymer and nanocomposites remained practically the same once the clay structure is predominantly of the intercalated type. In comparison with pure PMMA, glass transition temperature and storage modulus of polymer are notably increased by the presence of clay. It was found that the chain length of surfactant attached to the SWy-1 clay affects the Tg values. Glass transition temperatures of nanocomposites SWy-1-C16/PMMA were significantly higher than the values obtained for nanocomposites SWy-1-C8/ PMMA. This can be attributed to the modifying agent C16, which has a greater hydrophobic chain length. The organic tail can provide a better dispersion of the MMA monomer in the organoclay, resulting in a nanocomposite with predominant exfoliated structure. Another significant factor to be considered was the effect of solvent used in the nanocomposite preparation. Considering nanocomposites with the same chain length (C8 or C16), Tg values obtained for nanocomposites prepared with ethanol is higher than those observed for those prepared in acetonitrile. This was attributed to the influence of the average molecular weight; once the nanocomposites prepared in ethanol exhibited higher polymeric chains.
In the present study, we have attempted to investigate, for the first time, the photophysical behavior of 1,1'-diethyl-2,4'-cyanine (ICY)/clay mineral hybrids in the solid state. The effects promoted by ICY loading and clay type on the spectroscopic properties were studied by UV-vis diffuse reflectance spectroscopy (DR) and different fluorescence techniques. The hybrids were characterized by X-ray diffraction (XRD) and thermogravimetric analysis (TGA). UV-vis-DR revealed the formation of ICY H-aggregates in Wyoming montmorillonite (SWy-1) and Laponite (Lap); however, J-aggregates were predominant for ICY on Arizona (SAz-1) and Barasym (SYn-1) montmorillonites. The formation of J-aggregates was favored on clays with a high layer charge density (SAz-1 and SYn-1). Increasing ICY loading leads to an increase in H-aggregates, which become predominant in all of the samples. The fluorescence spectra of ICY-Lap and ICY-SYn-1 hybrids showed two emissive bands, and they were assigned to the monomeric and J-aggregate species. The fluorescence lifetime showed consistent and distinct values for the two species. The longer fluorescence lifetime can be assigned to the ICY monomers, while the second component has a short lifetime value and may be attributed to J-aggregate emission species. Moreover, confocal fluorescence micrographs showed two different fluorescent domains; monomers (greenish domain) and J-aggregates (orange domain) can be clearly distinguished. For ICY adsorbed on SWy-1 and SAz-1, the intensities of the fluorescence spectra were very low, and it was not possible to measure the fluorescence lifetimes due to high iron content in these clays, which acts as an efficient quencher of the excited singlet state of the dye molecules. XRD and TGA curves showed that the intercalation of ICY into the interlayer regions of SWy-1, SAz-1, and SYn-1 occurred for high dye concentration only. In the case of Laponite, ICY adsorbs on the external surface of the layer. Our studies indicate that the ICY-clays, in particular, ICY-SYn-1 and ICY-Lap, are promising hybrid materials with interesting optical and photophysical properties.
Poly(ethyleneoxide) (PEO) composites with SWy‐1 montmorillonite were prepared by mixing the polymer and the clay in aqueous colloidal solutions. Thin films of the composites were obtained by solvent evaporation and exposed to 254‐nm UV‐irradiation. The photodegradation was monitored by FTIR and the chain scission reaction was confirmed by measurement of average molecular weights using size exclusion chromatography. The rate of oxidation of pure PEO was much faster than that of the composites (SWy‐1/PEO). The SWy‐1 clay stabilizes the polymer against UV irradiation. This stabilization is due to two factors: on one side, the absorption of UV radiation by the clay, and on the other the scattering of the incident radiation by the particles; both contributing to minimize the degradation rate of the PEO present in the composites. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013
Photochemical method was used to synthesize silver nanoparticles (AgNPs) in the presence of citrate or clay (SWy-1, SYn-1, and Laponite B) as stabilizers and Lucirin TPO as photoinitiator. During the photochemical synthesis, an appearance of the plasmon absorption band was seen around 400 nm, indicating the formation of AgNPs. X-ray diffraction results suggested that AgNPs prepared in SWy-1 were adsorbed into interlamellar space, and moreover, showed some clay exfoliation. In the case of SYn-1, AgNPs was not intercalated. For the AgNP/Lap B sample, the formation of an exfoliated structure occurred. Transmission electron microscopy revealed the spherical shape of AgNPs for all samples. The particle sizes obtained for AgNP/SWy-1, AgNP/SYn-1, and AgNP/Lap B were 2.6, 5.1, and 3.8 nm, respectively. AgNPs adsorbed on SYn-1 reveal nonuniform size and aggregation of some particles. However, AgNP/SWy-1 and AgNP/Lap B samples are more uniform and have diameters smaller than those prepared with SYn-1. This behavior is due to the ability to exfoliate these clays. The antibacterial activities of pure clays, AgNP/citrate, and AgNP/clays were investigated against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). AgNPs in the presence of clays (AgNPs/SYn-1 and AgNPs/SWy-1) showed a lower survival index percentage compared to those obtained for pure clays and AgNPs. The AgNP/SWy-1 sample showed good antibacterial activity against both tested species and the lowest survival index of 3.9 and 4.3 against E. coli and S. aureus, respectively. AgNPs are located in the interlayer region of the SWy-1, which has acid sites. These acidic sites may contribute to the release of Ag(+) ions from the surface of AgNPs. On the other hand, Laponite B and AgNP/Lap B samples did not demonstrate any bactericidal activity.
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