Pendant chain dynamics in model PDMS networks probed by spin diffusion experiments

RODOLFO H. ACOSTA; MARÍA BELÉN FRANZONI; M. A. VILLAR; E.M. VALLÉS; GUSTAVO MONTI

Conferencia; 13 th, Auremn Conference; 2011

Model PDMS networks are ideal systems not only to probe the validity of the different models for the dynamics of the network but also offer the possibility to test the response of new pulse sequences. The density of cross-link points determines the elasticity of the networks. These can be either chemical cross-links or physical entanglements produced by the slow motion of pendant chains that are free to move inside a tube defined by the topology of the network. In this work we present results obtained with Double Quantum NMR to characterize the elasticity of several networks in which the amount of pendant material, thus the number of cross-link points, is varied. Additionally, the dynamics of pendant material are probed by using spin diffusion techniques. The magnetization gradient is generated in two different manners, first by selection of elastic chains via a DQ filter and afterwards selecting the pendant chains by use of a dipolar filter. The transfer of magnetization from one type of chain to the other is determined by inspection of CPMG decays and is due to a nuclear Overhauser effect.