Thermoset modified with polyethersulfone: Characterization and control of the morphology

Thermoset (TS) epoxy resins can be toughened with a thermoplastic (TP) for high-performance applications. The final structure morphology has to be controlled to achieve high mechanical properties and high impact resistance. Four polyethersulfone-modified epoxy resins are considered. They consist of different epoxy monomer structure (TGAP, triglycidyl-p-aminophenol and TGDDM, tetraglycidyl diaminodiphenylmethane) and a fixed amount of thermoplastic, and they are cured with two different amounts of curing agent. A reaction-induced phase separation occurs for all formulations generating morphologies, different in shapes and scales. The aim is to control the final morphology and in particular its dominant length scale. This morphology depends on the phase separation process, from the initiation to its final stage. The initiation relies on the relative miscibility of the components and on the stoichiometry between epoxy and curing agent. The kinetics depends on the viscosity of the systems. The different morphologies are characterized by electron microscopy or neutron scattering. Dynamic mechanical analysis allows confirming the presence of a phase separation even when it is not observable by electron microscopy. Vermicular morphologies with few hundreds nanometer width are obtained for the systems containing the TGAP as epoxy monomer. Systems formulated with TGDDM presents morphologies on much smaller scale of order a few tens of nanometers. We interpret the different sizes of the morphologies as a consequence of a larger viscosity for the TGDDM systems as compared to the TGAP ones rather than by a latter initiation of phase separation.     

Design of new imidazole derivatives with anti-HCMV activity: QSAR modeling,synthesis and biological testing

Journal of Computer-Aided Molecular Design - The problem of designing new antiviral drugs against Human Cytomegalovirus (HCMV) was addressed using the Online Chemical Modeling Environment (OCHEM)....     

Conformational analysis of cellulose acetate in the dense amorphous state

Atomistic simulations of cellulose acetates (CAs) differing in their degree of substitution have been performed and analyzed in terms of conformation and interaction schemes. The stabilization of the structure of these cellulose derivatives is understood as a subtle balance between hydrogen bonds and the dipolar acetate-acetate interactions that are associated with important changes in the macromolecular conformation. On the one hand, cellulose and cellulose triacetate (CTA) are characterized by a single stabilization process (H-bonds and dipolar interactions respectively), showing a similar structure in their melt phase together with similar radii of gyration. On the other hand partially acetylated CAs combine both the conformational properties of cellulose and CTA but present an unexpected conformational domain, named C2, which induces a local hydrophobic pocket. These CAs are also further stabilized by hydrogen bonds between the hydroxyl and acetyl groups. Although idealized, the proposed models are realistic since they are in good agreement with literature experimental results.     

Optical bistability in semiconductor lasers

Optical and Quantum Electronics -