Nanocomposites and nanomaterials
EPR characterization of FEP-PAA-Ag nanoparticles composite. 
Melnyk A.K.1, Kislyuk V.V.2, Bondar Yu.V.3, Trachevskij V.V.4
1Institute for Sorption and Problems of Endoecology of the NAS of Ukraine. Naumov str.,13, Kyiv- 03164, Ukraine 
E-mail: mak106@ukr.net
2G.V. Kurdyumov Institute for Metal Physic of the NAS of Ukraine. Vernadsky blvd.,36, Kyiv- 03142, Ukraine 
3 State Institution "Institute of Environmental Geochemistry” of the NAS of Ukraine. Palladin ave.,34a, Kyiv- 03680, Ukraine
4Technical centre, NAS of Ukraine. Pokrovska str.,13, Kyiv- 04070, Ukraine  

Permanent interest to the noble metal nanospecies is mostly caused by their biocompatibility, appearance of new optical and electrical properties absent in the bulk materials. The application of a supporting matrix is one of the revolutionary approaches to guarantee the separation of the nanoparticles. It was previously shown that such composite materials may also have paramagnetic properties, therefore, studies involving magnetic resonance methods, including EPR, can provide new information about them. 
In our current work, silver clusters were formed in a system, consisting of fluorinated ethylene propylene copolymer (FEP) activated through the radiation-induced graft polymerization of acrylic acid monomer (AA) for the introduction of chemically active carboxyl groups onto the surface of FEP films.   Temperature dependent conformational modifications, reflecting the changes of the local interactions between adjacent nano-fragments, were monitored via electron paramagnetic resonance spectroscopy. EPR spectra of silver nanoparticles in the grafted matrix consist of the superposition of two signals with correspondent values of g-factors: g┴~2.036, gǁ~2.02, geff = 2.031. The behavior of the spectra while temperature decreases from the room temperature to 225 K reflects the redistribution of the contributions from paramagnetic particles: intensity of the line attributed to the paramagnetic centers with geff = 2.03, ΔH=7 mT increases which is accompanied by the decrease of the signal with parameters of spin-Hamiltonian characteristic for axial symmetry. An exchange interaction between them can be suppressed under higher temperatures due to vibrational modes of the separating fragments of the matrix molecule. The intensity of the exchange interaction at room temperature correlated with the data obtained by SEM - for particles of an elongated shape with more dense “packing” it was higher than for spherical particles with a larger average distance between clusters.