Structure, local ordering and mechanical properties of free-standing Uretane/Urea elastomer films undoped and doped with ferro-nanoparticles

Antonio Martins Figueiredo Neto ,C. Sena ,M. H. Godinho ,P. J. Sebastião 2,D. Sousa 3

Instituto de Física, Universidade de São Paulo, caixa postal 66318, 05314-970, São Paulo, São Paulo, Brazil
Faculdade de Ciências e Tecnologia e CENIMAT/I3N, Universidade Nova de Lisboa, Quinta da Torre, P-2829-519 Caparica, Portugal.
2Centro de Física da Matéria Condensada, Av. Prof. Gama Pinto 2, 1649-003, Lisboa, Portugal, and Departamento de Física, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais 1, 1049-001 Lisboa, Portugal
3DEEC AC-Energia, Instituto Superior Técnico, TU Lisbon, Av. Rovisco Pais 1, 1049-001, Lisboa, Portugal

We report on an experimental study of the structures of non-liquid crystalline elastomers of PU/PBDO without and with ferromagnetic nanoparticles incorporated. The study is made by using the X-ray diffraction and nuclear magnetic resonance techniques. The structure proposed for the undoped cross-linked polymer network, with characteristic distance between parallel molecules of the order of 0.46 nm is almost independent on the stretching applied. The shear casting performed in order to obtain the elastomeric films introduces an anisotropy in the backbone which tends to orient the stick-like molecules parallel to the flow. In the case of nanoparticles-doped samples, a diluted and a concentrated regimes were observed. In the dilute regime the elastomeric structure is practically unchanged when compared to that from the undoped samples. In the concentrated regime, the particles act like incrustations in the elastomeric matrix, pushing and organizing the segmentes between cross-linked molecules in their neighborhood. In this picture, near the particles' surfaces, the organized segment's structure, that we pictured as a quasi-HCP structure of the parallel segment molecules, mainly orient parallel to the casting direction.

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