Foi investigada a relação entre as propriedades dielétricas (constante dielétrica, ε'; fator de perda, ε"; energia de ativação, E a ) e a proporção de resina epóxi (OG) para endurecedor em polímeros termorrígidos de resina epóxi (OG). A amplitude do pico de ε" decresce com o aumento da porcentagem em massa de OG até aproximadamente 73% e aumenta levemente para maiores % OG. A temperatura da posição do pico de ε" aumenta com o aumento da % OG, alcançando valores máximos para formulações no intervalo de 67 a 73%, e então, decresce acentuadamente para maiores % OG. A energia de ativação obtida por relaxação dielétrica aumentou com a % OG até aproximadamente 70%. Um aumento adicional na % OG até 83% reduz a E a . As curvas das propriedades mecânicas de módulo de tensão e resistência à fratura como função da % em massa de OG apresentaram um comportamento similar.The relationship between the dielectric properties (dielectric constant, ε', and loss factor, ε"; activation energy, E a ) and the ratio of epoxy resin (OG) to hardener of the epoxy resin thermosetting polymers was investigated. The amplitude of the ε" peak decreases with increasing OG content until about 73 wt.% and slightly increases at higher OG content. The temperature of the position of the ε" peak increases with the increasing of OG content, reaching maximum values for compositions in the range of 67 and 73 wt.%, and then it decreases sharply at higher OG content. The activation energy obtained from dielectric relaxation increased with increasing wt.% OG up to around 70 wt.%. Further increase in concentration of OG up to 83 wt.% reduced E a . The curves of tensile modulus and fracture toughness mechanical properties as a function of OG content presented a similar behavior.

Título: Materiais nanoestruturados do sistema epoxídico DGEBA/dietilenotriamina modificado com um éster de silsesquioxano: propriedades mecânicas e térmicas.

Organo-clay complex of ligand-hexadecyltrimethylammonium with montmorillonite was made for the purpose of application as a preconcentration agent in a chemically modified carbon paste electrode for determination of mercury (II) in aqueous solution. It was found out that the adsorption of Hg(II) by organo-clay complex is independent of the pH of the solution. It was also found out that the adsorption of the remaining metals Cd(II), Pb(II), Cu(II), Zn(II), and Ni(II) was dependent on the changes in pH solutions and increased when it varies from 1 to 8. The resultant material was characterized by cyclic and differential pulse anodic voltammetry using a modified graphite paste electrode in different supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, possible interferences and other variables.

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