PS-HEMA latex fractionation by sedimentation and colloidal crystallization

A poly(styrene-co-hydroxyethylmethacrylate) latex underwent sedimentation under gravity followed by an spontaneous and extensive colloidal crystallization. It was then fractionated in three visually distinguishable layers. Latex aliquots layers were sampled at different heigths and the particles were characterized by PCS, microelectrophoresis, infrared spectra and analytical electron microscopy. The major fraction was opalescent and contained the colloidal crystals settled in the bottom of the liquid. Two other latex fractions were obtained, which differed in their chemical compositions, particle sizes and topochemical features from the self-arraying particles. Macrocrystallization of the fractionated latex yielded high quality crystals with a low frequency of defects, which confirms that particle chemical homogeneity is an important factor for particle self-arraying.Látex de poli(estireno-co-hidroxiacrilato de metila) separa-se em três camadas visualmente distinguíveis, das quais a inferior é opalescente e contém cristais coloidais. Alíquotas do látex foram coletadas em diferentes alturas, e as partículas foram caracterizadas, por espalhamento de luz dinâmico, microeletroforese, IV e microscopia eletrônica analítica. A fração inferior contém a maior parte do polímero, sendo formada por partículas de dimensões e composição química uniformes. As partículas coletadas das duas outras frações são diferentes das que formam os cristais coloidais, em praticamente todos os aspectos. A secagem da fração opalescente produz macrocristais de alta qualidade, com baixa frequência de defeitos, mostrando que a homogeneidade química das partículas é um fator importante, na sua auto-organização.497504Fundação 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

Systematic study of luminescent properties of new lanthanide complexes using crown ethers as ligand

AbstractThis is a report on the synthesis, characterization and spectroscopic study of 24 lanthanide-crown ether coordination compounds, where Eu(III), Tb(III) and Gd(III) were complexes to 12-crown-4 (12C4), 15-crown-5 (15C5), 1,10-phenanthroline (phen) and 2,2′-dipyridyl (dipy). The compounds were synthesized in an ethanol/acetone solution at room temperature and analyzed using CHN elemental analysis and infrared, absorption and emission spectroscopies. The polarizability that the ligand exerts on the emission process was verified and found remarkable. The Eu-15C5-phen complex showed the highest quantum efficiency (71.6%) because of its low non-radiative rate and highest polarizability with reference to the ligands system

Quality of postharvest strawberries: comparative effect of fungal chitosan gel, nanoparticles and gel enriched with edible nanoparticle coatings

This study compared, for the first time, the postharvest conservative action of edible fungal chitosan coatings (gel, nanoparticles and gel-nanoparticle) on the physico-chemical, sensorial and microbiological characteristics of strawberries. The nanoparticles were prepared by an ionic gelation method and characterized by dynamic light scattering and scanning electron microscopy. The antioxidant (DPPH* and ABTS*) activity of the edible coatings and the antimicrobial (macrodilution method) action against phytopathogenic fungi were verified. The nanoparticles had a size of 331.1 nm and a zeta potential of + 34 mV. The gel, nanoparticles and gel+nanoparticles exhibited minimum inhibitory concentration values ranging from 4 to 5, 1.5 to 2.5 and 1.0 + 0.5 to 2.0 + 1.5 g.L−1, respectively. All the edible coatings exhibited antifungal action. All the coatings had high scavenging activity, especially the gel edible coating. The coatings, especially the gel+nanoparticles, decreased the weight loss, microbiological growth, soluble solids, maturity index and moisture loss of the strawberry and preserved the pH values, anthocyanin content, titratable acidity and sensory characteristics. Therefore, the use of chitosan edible coating containing nanoparticles can be a promising strategy to improve the post-harvest quality of strawberries.info:eu-repo/semantics/publishedVersio

Aluminum polyphosphate gels structural evolution probed by NMR spectroscopy

The aim of this work was to investigate how the structure of aluminum polyphosphate gels change upon aging and drying. This is essential if one is interested in using a gel as a matrix to synthesize organic-inorganic hybrid materials. The liquid and solid samples were characterized by 27Al and 31P NMR spectroscopy. Larger polyphosphate chains make the main contribution to gel formation and the smaller units are expelled into the supernatant solution. Polyphosphate chains undergo hydrolysis and chain scission upon gelation. Samples aged in a moisture-rich environment turn into viscous liquids as a consequence of water uptake, followed by extensive hydrolysis. Samples exposed to low relative humidity environments dry yielding brittle samples in which larger chains are stable. Vacuum-dried samples still contain ca. 30%-weight water

Quimica do estado solido : preparação, caracterização, comportamento termico e reações topoquimicas em tiometalatos do tipo AM52 (A=K, Ag, Ba e M=Fe)

Orientador : Oswaldo Luiz AlvesDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de QuimicaMestrad

Electric Fields Enhance Ice Formation from Water Vapor by Decreasing the Nucleation Energy Barrier

Video images of ice formation from moist air under temperature and electric potential gradients reveal that ambient electricity enhances ice production rates while changing the habit of ice particles formed under low supersaturation. The crystals formed under an electric field are needles and dendrites instead of the isometric ice particles obtained within a Faraday cage. Both a non-classical mechanism and classical nucleation theory independently explain the observed mutual feedback between ice formation and its electrification. The elongated shapes result from electrostatic repulsion at the crystal surfaces, opposing the attractive intermolecular forces and thus lowering the ice-air interfacial tension. The video images allow for the estimation of ice particle dimensions, weight, and speed within the electric field. Feeding this data on standard equations from electrostatics shows that the ice surface charge density attains 0.62–1.25 × 10−6 C·m−2, corresponding to 73–147 kV·m−1 potential gradients, reaching the range measured within thunderstorms. The present findings contribute to a better understanding of natural and industrial processes involving water phase change by acknowledging the presence and effects of the pervasive electric fields in the ambient environment

Supramolecular ionics: electric charge partition within polymers and other non-conducting solids

Electrostatic phenomena in insulators have been known for the past four centuries, but many related questions are still unanswered, for instance: which are the charge-bearing species in an electrified organic polymer, how are the charges spatially distributed and which is the contribution of the electrically charged domains to the overall polymer properties? New scanning probe microscopies were recently introduced, and these are suitable for the mapping of electric potentials across a solid sample thus providing some answers for the previous questions. In this work, we report results obtained with two of these techniques: scanning electric potential (SEPM) and electric force microscopy (EFM). These results were associated to images acquired by using analytical electron microscopy (energy-loss spectroscopy imaging in the transmission electron microscope, ESI-TEM) for colloid polymer samples. Together, they show domains with excess electric charges (and potentials) extending up to hundreds of nanometers and formed by large clusters of cations or anions, reaching supramolecular dimensions. Domains with excess electric charge were also observed in thermoplastics as well as in silica, polyphosphate and titanium oxide particles. In the case of thermoplastics, the origin of the charges is tentatively assigned to their tribochemistry, oxidation followed by segregation or the Mawell-Wagner-Sillars and Costa Ribeiro effects.A eletrificação de sólidos é conhecida há quatro séculos, mas há muitas questões importantes sobre este assunto, ainda não respondidas: por exemplo, quais são as espécies portadoras de cargas em um polímero isolante eletrificado, como estas cargas estão espacialmente distribuídas e qual é a contribuição destas cargas para as propriedades do polímero? Técnicas microscópicas introduzidas recentemente são apropriadas para o mapeamento de potenciais elétricos ao longo de uma superfície sólida, portanto podem responder a uma destas questões, contribuindo para a resolução das outras. Este trabalho resenha resultados obtidos combinando-se as microscopias de varredura de potencial elétrico (SEPM) e de força elétrica (EFM) com a microscopia eletrônica analítica baseada na espectroscopia de perda de energia de elétrons (ESI-TEM). Os materiais examinados são colóides poliméricos (látexes), polímeros termoplásticos, nanopartículas e híbridos. Nos materiais particulados foram observados domínios com excesso de cargas elétricas, estendendo-se por dezenas e centenas de nanômetros, formados por grandes acúmulos de cátions ou ânions atingindo dimensões supramoleculares. No caso dos termoplásticos, a formação dos domínios elétricos ainda não está bem compreendida, sendo tentativamente atribuída a efeitos triboquímicos no processamento do plástico, à formação de domínios oxidados, à ação de radiação de alta energia no ambiente ou aos efeitos Mawell-Wagner-Sillars e Costa Ribeiro