engleski

The use of electron spin resonance in studying chain dynamics of organic-inorganic polymer samples and the synergy between organic and inorganic component

Electron spin resonance (ESR) spectroscopy has been widely used to obtain information about motional behavior and relaxation processes in polymers. Majority of polymers, possess no intrinsic paramagnetism and therefore do not give rise to an ESR spectrum. However, it is possible to apply this technique as an indirect method in studying such materials. One way is by introducing stable free radicals into a polymer matrix. But if the polymer matrix is reinforced by filler particles which already give rise to a resonant ESR spectrum, e.g. carbon-based materials, than the ESR spectroscopy could give some information about the material without the introduction of free radicals. In this study elastomer based samples with different ratios of multi walled carbon nanotubes (MWCNT) and expanded organomodified montmorillonite (EOMt) were investigated by ESR spectroscopy. Two approaches were used. One was investigation of the spin probed samples where TEMPONE, 4-oxo derivative of TEMPO (2, 2, 6, 6-tetramethylpiperidin-1-oxyl), was used as a spin probe. The other was investigation of the samples without the free radicals, analyzing the ESR spectra measured only by the MWCNT present in the nanocomposites The results showed that, in the first case, the choice of TEMPONE as a spine probe was right giving good ESR signal when incorporated into the samples, meaning that it is able to follow the motional behavior of the polymer chains. Also the choice of its concentration proved to be good, taking into account the interactions that can occur with the complex system of these nanocomposites. On the other hand, the process of solvent evaporation should be still optimized. The trapped small amount of solvent in the higher density regions of the samples showed to be the biggest problem in the sample preparation. The ESR spectra of the samples that weren’t spin probed showed narrow, symmetrical, and intense lines characteristic for carbon nanotubes. These Lorentzian shapes of the resonance spectra indicated the good dispersion of the nanotubes within the polymer matrix, regardless of the presence of EOMt. On the other hand, the established dependence of the double integral of resonance spectra on the amount of EOMt showed a sharp decrease after introduction of a certain quantity into the matrix. This suggested that above a certain amount of EOMt, present in the matrix, a synergism engenders between these two nanofillers, EOMt and MWCNT.

Electron spin resonance, ESR, elastomer, multiwall carbon nanotubes, organically modified montmorillonite, chain dynamics

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