Domain sizes in heterogeneous polymers by spin diffusion using single-quantum and double-quantum dipolar filters.

Area of Science:

• Materials Science
• Polymer Chemistry
• Analytical Chemistry

Background:

• Characterizing microdomain structures in heterogeneous polymer systems is crucial for understanding material properties.
• Nuclear Magnetic Resonance (NMR) is a powerful tool for probing molecular environments.
• Spin-diffusion NMR experiments provide insights into domain morphology and connectivity.

Purpose of the Study:

• To develop and apply a double-quantum (DQ) dipolar filter NMR method for characterizing microdomain structures in polymer blends.
• To analyze the spin-diffusion process using a model morphology with three distinct domains.
• To determine the sizes of crystalline, interface, and amorphous domains in specific polymer systems.

Main Methods:

• 1H spin-diffusion experiments utilizing a DQ dipolar filter.
• Analysis of the NMR spin-diffusion process based on a three-domain model.
• Obtaining general analytical solutions for z magnetization source and sink for a 1D lamellar morphology.
• Applying the method to polystyrene-poly(ethylene oxide) (PS-PEO) and poly(hydroxyethylmethacrylate)-poly(ethylene oxide) (PHEMA-PEO) diblock copolymers.

Main Results:

• General analytical solutions for spin-diffusion in a 1D lamellar morphology were derived.
• Domain sizes (crystalline, interface, amorphous) were successfully determined for PS-PEO and PHEMA-PEO.
• The DQ dipolar filter demonstrated good efficiency for PS-PEO.
• Partial efficiency of the DQ filter was observed for the mobile domains in PHEMA-PEO.

Conclusions:

• The DQ dipolar filter NMR technique is effective for characterizing microdomain structures in heterogeneous polymer samples.
• The method allows for the determination of domain sizes, offering a valuable alternative to traditional dipolar filters.
• The efficiency of the DQ filter can vary depending on the specific polymer system and its domain characteristics.