Effect of Nonionic Surfactants on the Crystallinity and Thermal Stability of Poly(vinyl alcohol) Film

In this study, poly(vinyl alcohol) (PVA)/surfactant films were prepared by casting technique. Two nonionic surfactants with different alkyl chain lenghts (Tween 20 and Tween 40) were used. PVA/Tween 20 and PVA/Tween 40 films were characterized by means of Fourier Transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). FTIR spectra of PVA/Tween films indicated the presence of hydrogen bond interactions between the Tween surfactants and PVA. XRD results showed that the incorporation of Tween 20 and 40 into the PVA film decreased the crystallinity of PVA.TGA curves revealed an increase in the thermal stability of PVA film in the presence of the surfactants. DOI: http://dx.doi.org/10.17807/orbital.v12i4.151

Effect of Nonionic Surfactants on the Crystallinity and Thermal Stability of Poly(vinyl alcohol) Film

In this study, poly(vinyl alcohol) (PVA)/surfactant films were prepared by casting technique. Two nonionic surfactants with different alkyl chain lenghts (Tween 20 and Tween 40) were used. PVA/Tween 20 and PVA/Tween 40 films were characterized by means of Fourier Transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and thermogravimetric analysis (TGA). FTIR spectra of PVA/Tween films indicated the presence of hydrogen bond interactions between the Tween surfactants and PVA. XRD results showed that the incorporation of Tween 20 and 40 into the PVA film decreased the crystallinity of PVA.TGA curves revealed an increase in the thermal stability of PVA film in the presence of the surfactants. DOI: http://dx.doi.org/10.17807/orbital.v12i4.151

A hybrid material assembled by anthocyanins from acai fruit intercalated between niobium lamellar oxide

Organic-inorganic hybrid materials can be prepared dispersing organic species into well-defined inorganic nanoblocks. This paper describes the immobilization of natural dyes from the extract of the Brazilian acai-fruit into two types of layered hexaniobate precursors derived from H(2)K(2)Nb(6)O(17): (i) colloidal dispersion of niobate exfoliated nanoparticles and (ii) niobate pre-intercalated with tetraethylammonium cations (TEA(+)). the restacking of exfoliated particles in the presence of acai anthocyanins promotes their intercalation and produces stacked layers showing large basal spacing (ca. 50 angstrom). the TEA(+) pre-intercalated niobate provides particles with lower content of dye species than the exfoliated precursor but with higher degree of organization and regularity according to X-ray diffraction data and images obtained by electron microscopies. Vibrational (FTIR and Raman) and (13)C NMR spectroscopies indicate the presence of flavylium cations in the hybrid materials and spectral profiles characteristic of glycosylated anthocyanidins. According to thermal analysis results, the purplish hybrids materials are more stable than the free acai-dyes. One hybrid sample was heated under air up to 170 degrees C and maintained at this temperature for 240 min. No weight loss events were observed and the sample retained its original color, indicating that the intercalation of anthocyanin into hexaniobate increases its thermal stability. Considering the structural, chemical, optical and thermal properties of the synthesized hybrid materials, they might be good candidates to be investigated for future specialized applications.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)Instituto do Milenio de Materiais ComplexosUniv São Paulo, Inst Quim, BR-05508000 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Ciencias Exatas & Terra, BR-09972270 Diadema, SP, BrazilUniv Clermont Ferrand, Lab Mat Inorgan, CNRS, UMR 6002, F-63177 Clermont Ferrand, FranceUniversidade Federal de São Paulo, Dept Ciencias Exatas & Terra, BR-09972270 Diadema, SP, BrazilCAPES: 557/07FAPESP: 06/516510Web of Scienc

Chemical modification of niobium layered oxide by tetraalkylammonium intercalation

Chemical modification of the layered K4Nb6O17 material was systematically investigated through the reaction of its proton-exchanged form (H2K2Nb6O17) in alkaline solutions containing tetramethylammonium (tma+), tetraethylammonium (tea+) or tetrapropylammonium (tpa+) cations. The intercalated amount reaches 50% (for tma+), 25% (for tea+) and 15% (for tpa+) of the H2K2Nb6O17 negative charge (concerning the exchange at interlayer I) due to the steric hindrance of larger cations. Hexaniobate samples present (020) basal reflections equal to 23.0, 26.3 and 26.5 Å once intercalated respectively with tma+, tea+ and tpa+. When samples are heated above 200-250 ºC, CO2 evolution is observed; Hofmann elimination reaction is also detected for hexaniobate-tpa+ samples. Scanning electron microscopy images show the predominance of plate-like particles; stick-like particles are also observed for samples containing bulky ions. The intercalation reaction is promoted in the order tma+ > tea+ > tpa+, while the formation of a dispersion of colloidal particles is facilitated in the inverse order.A modificação química do material lamelar K4Nb6O17 foi investigada sistematicamente através da reação de sua forma protônica (H2K2Nb6O17) em soluções alcalinas contendo os cátions tetrametilamônio (tma+), tetraetilamônio (tea+) ou tetrapropilamônio (tpa+). A quantidade intercalada corresponde a 50% (para tma+), 25% (para tea+) e 15% (para tpa+) da carga negativa do H2K2Nb6O17 (considerando a troca iônica na região interlamelar I). As amostras de hexaniobato apresentam reflexões basais (020) de 23,0, 26,3 e 26,5 Å quando intercaladas, respectivamente, com tma+, tea+ e tpa+. Aquecendo-se as amostras acima de 200-250 ºC, observa-se a liberação de CO2; a reação de eliminação de Hofmann também é observada para as amostras de hexaniobato-tpa+. As imagens de microscopia eletrônica de varredura mostram a presença predominante de partículas em forma de placas; partículas em forma de bastões também são observadas nas amostras contendo íons volumosos. A reação de intercalação é promovida na ordem tma+ > tea+ > tpa+, enquanto a formação de uma dispersão de partículas coloidais é facilitada na ordem inversa

Layered niobate nanosheets: building blocks for advanced materials assembly

Layered materials with intracrystalline reactivity undergo intercalation and pillaring reactions to produce materials with useful properties for catalysis, electrodes for Li batteries and adsorbents. New possibilities for the use of layered inorganic solids came out from the layered structures capable of delamination. the exfoliated particles are considered a new class of nanomaterial based on single crystal nanosheets. Due to their unique morphological features and properties, these nanosheets can be used as building blocks for nanomaterials with innovative properties. in this feature article we describe the aspects related to layered niobate exfoliation and the new possibilities that arises from the use of niobate nanosheets in the manufacturing of thin films, layer-by-layer (LbL) assemblies, hybrid structures, sensors and other materials.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Instituto do Milenio de Materiais ComplexosUniv São Paulo, Inst Quim, BR-05508000 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Ciencias Exatas & Terra, BR-09972270 Diadema, SP, BrazilUniversidade Federal de São Paulo, Dept Ciencias Exatas & Terra, BR-09972270 Diadema, SP, BrazilWeb of Scienc

A hybrid material assembled by anthocyanins from acai fruit intercalated between niobium lamellar oxide

Organic-inorganic hybrid materials can be prepared dispersing organic species into well-defined inorganic nanoblocks. This paper describes the immobilization of natural dyes from the extract of the Brazilian acai-fruit into two types of layered hexaniobate precursors derived from H(2)K(2)Nb(6)O(17): (i) colloidal dispersion of niobate exfoliated nanoparticles and (ii) niobate pre-intercalated with tetraethylammonium cations (TEA(+)). The restacking of exfoliated particles in the presence of acai anthocyanins promotes their intercalation and produces stacked layers showing large basal spacing (ca. 50 angstrom). The TEA(+) pre-intercalated niobate provides particles with lower content of dye species than the exfoliated precursor but with higher degree of organization and regularity according to X-ray diffraction data and images obtained by electron microscopies. Vibrational (FTIR and Raman) and (13)C NMR spectroscopies indicate the presence of flavylium cations in the hybrid materials and spectral profiles characteristic of glycosylated anthocyanidins. According to thermal analysis results, the purplish hybrids materials are more stable than the free acai-dyes. One hybrid sample was heated under air up to 170 degrees C and maintained at this temperature for 240 min. No weight loss events were observed and the sample retained its original color, indicating that the intercalation of anthocyanin into hexaniobate increases its thermal stability. Considering the structural, chemical, optical and thermal properties of the synthesized hybrid materials, they might be good candidates to be investigated for future specialized applications.Brazilian agencies FAPESPCNPqCAPES/COFECUB[557/07]Instituto do Milenio de Materiais ComplexosFAPESP[06/516510