NMR Studies of Polymer - Silica Nanoparticle Composites

1. NMR Studies of Polymer - Silica Nanoparticle Composites Christian E. Mejia, Christoph F. Weise, Steve Greenbaum, Hunter College Dept. of Physics and Astronomy Shane E. Harton, Columbia University Dept. of Chemical Engineering RESULTS NMR EXPERIMENTAL METHODS INTRODUCTION T2 (s)vs. Temperature (oC) T1 (s)vs. Temperature (oC) Throughout the years, polymer nanocomposites have shown great technological potential. These polymer nanocomposites are of great interest because of the ability of added nanoparticles to enhance the mechanical properties of polymers when mixed with them. These enhanced materials have a wide range of applications, from being used in airplane wings and automobile parts to being the new materials used in prosthetic implants. By studying nanoparticles, today’s materials could be further improved and developed into more efficient systems and sophisticated technologies. Various pulse sequences were used to acquire the different values T1, T2, and self-diffusion coefficients: T T1 pulse sequence: the time it takes for the magnetization to return to its equilibrium state is acquired from the resulting signal Diffusion (μm2/s) vs. % vol. Silica Diffusion (μm2/s) vs. 1/T (T-1) MATERIALS & PREPARATION • PMPS + Colloidal Silica CH3 T Diffusion Measurement: By applying two equal field gradients after a 90o and a 180o pulse, the diffusion coefficients can be calculated by measuring the signal decay Si O T2 (ms)vs. % vol. Silica n The decrease in T1 & T2 values, as compared to the “neat” polymer (no nanoparticles), indicate faster relaxation. This translates into slower diffusion measurements which are confirmed by the diffusion measurements recorded above CONCLUSIONS Scanning Electron Microscopy (SEM) image of silica particles (Tabatabaei, S., “Experimental study of the synthesis and characterization of silica nanoparticles via the sol-gel method”, Journal of Physics, Fig. 3) The repeating monomer in the PMPS polymer chain The T1 data suggests that the phenyl groups in the polymer interact more strongly with the nanoparticles, i.e. the phenyl T1 values are more greatly affected by the addition of nanoparticles. The T2 relaxation rates of the methyl and phenyl groups are affected to a similar extent by the increase of filler loading. This reflects a common mechanism, namely an alteration of polymer tumbling interaction with the particle surface. The difference in T1 and T2 values with filler loadings show that the confinement is both long range and local. The temperature dependence of the diffusion values show that the thermal activation of diffusive transport is independent of filler loading up to 10% by vol The samples were prepared in the Department of Chemical Engineering at Columbia University by Dr. Shane Harton. The PMPS used had a molcular mass of 2600g/mol and a degree of polymerization of 19. The diffusion values are lower in the nanocomposites compared to the “neat” polymer, but the curvature of the two sets of data are very similar, showing very little, if any, change in glass transition temperature and activation energy. Also, the measurements vs. % volume of silica show that the silica nanoparticles act as obstructions, causing slower diffusion measurements Sponsors: National Aeronautics and Space Administration (NASA) NASA Goddard Space Flight Center (GSFC) NASA Goddard Institute for Space Studies (GISS) NASA New York City Research Initiative (NYCRI) Contributors: Steve G. Greenbaum, Christoph F. Weise Shane E. Harton ACKNOWLEDGEMENTS Special thanks to Amish Khalfan for his help explaining NMR theory and for answering the millions of random questions I’ve had while at the lab.