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Sorption isotherm measurements by NMR.
Johannes Leisen1, Haskell W Beckham, Michael Benham
1School of Textile and Fiber Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0295, USA. johannes.leisen@tfe.gatech.edu
Solid State Nuclear Magnetic Resonance
|December 10, 2002
Summary
This study introduces automated NMR for sorption isotherms in cotton fabric. NMR relaxation times (T1 and T2*) depend solely on moisture content, not humidity history, revealing cellulose plasticization.
Area of Science:
- Materials Science
- Physical Chemistry
- Nuclear Magnetic Resonance (NMR) Spectroscopy
Background:
- Sorption isotherms are crucial for understanding material-environment interactions, particularly moisture uptake in textiles.
- Traditional methods for measuring sorption isotherms can be time-consuming and lack precision in controlling environmental conditions.
- Nuclear Magnetic Resonance (NMR) offers a non-destructive method to probe molecular dynamics and water interactions within materials.
Purpose of the Study:
- To develop and demonstrate an automated experimental setup for recording sorption isotherms using NMR.
- To investigate the relationship between NMR relaxation times (T1 and T2*) and moisture content in cotton fabric.
- To explore the phenomenon of hysteresis in NMR-based sorption isotherms and its correlation with gravimetric data.
Main Methods:
- An automated system was designed to control relative humidity (RH) with high precision during NMR experiments.
- Sorption isotherms were measured for cotton fabric by recording T1 and T2* relaxation times at discrete RH steps.
- NMR data (Bloch decays) were analyzed by fitting to multi-component relaxation functions, and results were compared to gravimetric sorption data.
Main Results:
- The automated NMR system successfully generated complete sorption isotherms for cotton fabric.
- A 'slow-relaxing component' in NMR signals exceeded gravimetrically determined moisture, attributed to plasticized cellulose.
- T1 and T2* relaxation times exhibited hysteresis, but were found to be dependent solely on moisture content (MC), not RH history.
Conclusions:
- Automated NMR is a powerful tool for characterizing material sorption behavior and molecular changes.
- The observed NMR hysteresis is linked to moisture content, indicating plasticization of the cellulose matrix.
- NMR relaxation parameters provide a history-independent measure of moisture content in cotton, offering insights into material state.