Abstract
Broadband dielectric spectroscopy measurements were performed on naturally dried cotton cloth, and a recently developed analytical technique for fractal analysis of water structures was applied to obtain existential states and locations of water molecules in the material. Three relaxation processes observed in GHz, MHz, and kHz frequency regions were attributed to dynamic behaviors of hydrogen bonding networks (HBNs) of water and interacting molecules, polymer chains with interacting ion and water molecules, and ions restricted on the interfaces of larger structures, respectively. Water molecules were heterogeneously distributed in the cotton cloth, and the HBNs remained as a broad GHz frequency process. Fractal analysis suggested that water molecules distributed in the material were characterized by a small value (0.55) of the Cole–Cole relaxation time distribution parameter, indicating spatial distribution of HBN fragments with various sizes in cotton cloth. This result was also supported by the T2 relaxation time obtained from nuclear magnetic resonance for naturally dried cotton yarn. Comparing previous results of dielectric relaxation measurements and fractal analysis with the τ–β diagram for various aqueous systems, the results determined that water molecules cannot exist inside cellulose microfibrils. The fractal analysis employed in this work can be applied to dynamic water structures in any material. The presented analytical technique with a universal τ–β diagram is expected to be an effective tool to clarify water structure detail even for heterogeneous hydrations of the low water content substances.Graphical abstract
Highlights
Cotton materials are naturally derived substances used in our daily lives
We examined a practical methodology of fractal analysis with the Broadband dielectric spectroscopy (BDS) measuring technique to clarify spatial distributions and fluctuations of water molecules in hydrogen bonding networks (HBNs) fragments for cotton cloth
Considering the typical experimental results obtained for moist materials in the frequency range, the GHz frequency process is attributed to cooperative dynamics of water molecules
Summary
Since the structure and physical property are affected by the water content, the hydration structure and mechanism in cotton [1,2,3] and the main component, cellulose [4,5,6,7,8,9] and related materials [10, 11] have been extensively studied. The hardening effect disappears with mechanical stimulus, and it is not shown in the completely dry state. These results suggest that the hardening effect brought by water molecules is not explained by only the average water content and the spatial distribution of water molecules in the dry sample. It is difficult to evaluate the spatial distribution of water molecules in a low water content sample especially for such heterogeneous materials
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