Effect of excluded volume on segmental orientation correlations in polymer chains

Area of Science:

• Polymer Physics
• Materials Science
• Spectroscopy

Background:

• Excluded volume interactions significantly influence polymer chain conformations.
• Nuclear Magnetic Resonance (NMR) is a powerful tool for probing molecular dynamics and structure.
• Understanding chain statistics in polymer gels is crucial for predicting material properties.

Purpose of the Study:

• To investigate the impact of excluded volume interactions on polymer chain segment orientation in gels.
• To establish nuclear magnetic resonance (NMR) as a direct measure of excluded-volume effects.
• To correlate tensor order parameter with gel correlation length.

Main Methods:

• Analytical calculations for single chains in good solvent and semidilute solutions.
• Computer simulations using the bond fluctuation model.
• Multiple-quantum NMR experiments on end-linked and randomly cross-linked polymer networks.

Main Results:

• NMR experiments directly quantify excluded-volume effects on chain statistics.
• A unique relationship between the tensor order parameter and correlation length (blob size) in equilibrium polymer gels was predicted.
• Experimental NMR data strongly supports the predicted relationship.

Conclusions:

• The tensor order parameter, measurable by NMR, provides unique insights into excluded volume effects in polymer gels.
• The predicted correlation between tensor order parameter and gel correlation length is experimentally validated.
• Observed initial decay of the tensor order parameter is attributable to solvent effects during swelling.