"Electron Spin Resonance (ESR) Approach in Studying Polymer Composites" (Mon, 1 July 2019)
Electron Spin Resonance (ESR) Approach in Studying Polymer Composites
by Srećko Valić, Ruđer Bošković Institute, Division of Physical Chemistry, Zagreb, Croatia
Monday, 1 July 2019 @ 12 pm
ICMAB - Sala d'Actes Carles Miravitlles
Electron spin resonance (ESR), also known as electron paramagnetic resonance (EPR), is a spectroscopic method able to detect paramagnetic centers (free unpaired electrons). It is possible to apply this technique in studying polymeric materials by introducing stable free radicals into a composite matrix. There are two common ways of the application of free nitroxide radicals: (i) they can be covalently attached to polymer chains or (ii) introduced mechanically (by diffusion) into a polymer (or composite) matrix. The former is named spin labeling and the latter spin probe method.
These techniques give the possibility to study local segmental motions of polymer chains, and particularly the influence of the filler on motional behavior of chain segments. An analysis of ESR spectra of a nitroxide diffusing in the polymer composite makes it possible to estimate the dynamic (in)homogeneity of the matrix and to calculate the amount of fast and slow component. Since the segmental dynamics play an important role in determining mechanical properties of the material, information obtained by ESR spectroscopy is important for practical application. Results obtained using several polymer composites will be presented: interpenetrating polymer networks and elastomers containing various fillers (silica, organically modified montmorillonite, zeolites and multiwall carbon nanotubes).
The formation of vacuoles on the surface of the filler in the case of a weak filler-matrix interaction will be elucidated. Moreover, it will be demonstrated how the ESR spectroscopy can be used as a new method to analyze the synergy between two different nanofillers dispersed in an elastomer matrix.
Hosted by Clara Viñas, Inorganic Materials and Catalysis Group
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