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Pulsed Field Gradient NMR Study of the Effect of Charge and Hydrophobicity on Diffusion in the Supramolecular Structure of Wet Cotton

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Alexei Ouriadov, B. Newling* and S. N. Batchelor*

Department of Physics, University of New Brunswick, P.O. Box 4400, Fredericton, New Brunswick, E3B 5A3, Canada, and Unilever Research Port Sunlight, Quarry Road East, Bebington, Wirral CH63 3JW, Great Britain

J. Phys. Chem. C, 2008, 112 (40), pp 15860–15864

DOI: 10.1021/jp8049944

Publication Date (Web): August 28, 2008

* To whom correspondence should be addressed. E-mail: stephen.batchelor@unilever.com (S.N.B.); bnewling@unb.ca (B.N.).

Section:

Textiles and Fibers

Abstract

To investigate the effect of charge and hydrophobicity on translational diffusion in cellulose fibers, PFG NMR experiments are reported on H₂O, methanol, pentanol, sodium methyl sulfonate and tetra-methylammonium chloride in wet cotton fibers. The results are analysed in terms of a 2-site exchange model (water/cotton) taking into account the different regions within cotton. For methanol, sodium, methyl sulfonate and tetramethylammonium chloride, free-diffusion within the cellulose nano-pores of cotton is observed, with diffusion coefficients 3.3, 7.3 and 10.8% lower than their bulk solution values, respectively. Internal exchange from the micron sized solvent pools between the growth rings of the fiber and the nano-pores within the cellulose structure takes approximately 10 ms for these 3 probes, which is much faster than exchange with the bulk solvent surrounding the fiber. Charge has little observable effect on the behaviour, except to slow the exchange of probes between the fiber and the bulk solution. For pentanol and water the micron sized solvent pools are observed as cages, indicating much slower internal exchange and is assigned to exclusion of the hydrophobic pentanol from the hydrophilic nano-pores and strong hydrogen bonding effects respectively. Accessible volumes in cotton are extracted from the data, which are in agreement with literature.

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