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Published on: August 20, 2013
NMR relaxation and pulsed-gradient diffusion study of polyethylene nanocomposites
R Ozisik1, J Zheng, P J Dionne
1Department of Materials Science and Engineering, Rensselaer Polytechnic Institute, MRC-205, Troy, New York 12180-3590, USA. ozisik@rpi.edu
The Journal of Chemical Physics
|October 15, 2005
Summary
Nuclear-magnetic-resonance (NMR) experiments reveal that polyethylene chain diffusion is unaffected by zinc oxide nanofillers. However, spin-spin relaxation experiments show significant changes in molecular rigidity, especially with smaller zinc oxide particles.
Area of Science:
- Materials Science
- Polymer Physics
- Nanotechnology
Background:
- Polyethylene (PE) is a widely used polymer, and its properties can be modified by incorporating nanofillers like zinc oxide (ZnO).
- Understanding the molecular dynamics and chain mobility in filled polymer systems is crucial for developing advanced materials.
Purpose of the Study:
- To investigate the effect of zinc oxide nanofiller content and particle size on the molecular dynamics of polyethylene.
- To analyze changes in polyethylene chain diffusion and relaxation behavior using nuclear-magnetic-resonance (NMR) techniques.
Main Methods:
- Pulsed-gradient spin-echo NMR experiments were conducted on polyethylene samples with varying molecular weights (808–33,000 g/mol).
- Four different zinc oxide particle sizes (27, 33, 51, and 2500 nm) were used as nanofillers.
- Spin-spin relaxation experiments were performed to probe the molecular environment.
Main Results:
- Polyethylene chain diffusion coefficients remained unchanged with increasing zinc oxide nanofiller content.
- Significant alterations were observed in the NMR relaxation spectrum, particularly in spin-spin relaxation.
- The smallest zinc oxide particles induced the most rigid molecular environment at fixed PE molecular weight near entanglement.
- This rigidity effect diminished at higher polyethylene molecular weights, indicating dominance by entanglements.
Conclusions:
- Zinc oxide nanofillers do not influence polyethylene chain diffusion but significantly impact molecular mobility and rigidity.
- Particle size plays a critical role in determining the extent of molecular rigidity induced by nanofillers.
- Polymer entanglements become the dominant factor governing molecular behavior at high molecular weights, overshadowing nanofiller effects.
