Electron Paramagnetic Resonance and Solid‐State NMR Studies of the Surfactant Interphase in Polymer–Clay Nanocomposites

Jeschke, Gunnar

doi:10.1002/9783527654505.ch9

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“…The temperature evolution of CW EPR spectra of surfactant spin labels were shown to be sensitive to several temperature activated processes occurring in the surfactant layer or polymeric region such as order-disorder transition of the surfactant layer, melting of the crystalline polymer domains or glass transition of the polymer [ 11 ]. Since our polymers do not have crystalline domains at any temperature and their glass transition temperature, as it was measured by DSC (Differential Scanning Calorimetry), is close to the temperature range where EPR looses sensitivity, we can rule out that these are the processes causing the observed dynamic change.…”

Section: Resultsmentioning

confidence: 99%

Structural Characterization of Polymer-Clay Nanocomposites Prepared by Co-Precipitation Using EPR Techniques

2014

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Polymer-clay nanocomposites (PCNCs) containing either a rubber or an acrylate polymer were prepared by drying or co-precipitating polymer latex and nanolayered clay (synthetic and natural) suspensions. The interface between the polymer and the clay nanoparticles was studied by electron paramagnetic resonance (EPR) techniques by selectively addressing spin probes either to the surfactant layer (labeled stearic acid) or the clay surface (labeled catamine). Continuous-wave (CW) EPR studies of the surfactant dynamics allow to define a transition temperature T* which was tentatively assigned to the order-disorder transition of the surfactant layer. CW EPR studies of PCNC showed that completely exfoliated nanoparticles coexist with agglomerates. HYSCORE spectroscopy in PCNCs showed couplings within the probe −assigned with DFT computations− and couplings with nuclei of the environment, 1H and 23Na for the surfactant layer probe, and 29Si, 7Li, 19F and 23Na for the clay surface probe. Analysis of these couplings indicates that the integrity of the surfactant layer is conserved and that there are sizeable ionic regions containing sodium ions directly beyond the surfactant layer. Simulations of the very weak couplings demonstrated that the HYSCORE spectra are sensitive to the composition of the clay and whether or not clay platelets stack.

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Section: Resultsmentioning

confidence: 99%