Abstract
The development of new materials emphasizes greater use of sustainable and eco-friendly resources, including those that take advantage of the unique properties of nanopolysaccharides. Advances in this area, however, necessarily require a thorough understanding of interactions with water. Our contribution to this important topic pertains to the swelling behavior of partially deacetylated nanochitin (NCh), which has been studied here by quartz crystal microgravimetry. Ultrathin films of NCh supported on gold-coated resonators have been equilibrated in aqueous electrolyte solutions (containing NaF, NaCl, NaBr, NaNO3, Na2SO4, Na2SO3, or Na3PO4) at different ionic strengths. As anticipated, NCh displays contrasting swelling/deswelling responses, depending on the ionic affinities and valences of the counterions. The extent of water uptake induced by halide anions, for instance, follows a modified Hofmeister series with F– producing the highest swelling. In marked contrast, Cl– induces film dehydration. We conclude that larger anions promote deswelling such that water losses increase with increasing anion valence. Results such as the ones reported here are critical to ongoing efforts designed to dry chitin nanomaterials and develop bio-based and sustainable materials, including particles, films, coatings, and other nanostructured assemblies, for various devices and applications.
Highlights
The field of bio-derived materials is rapidly developing due to their important attributes, such as sustainability, biodegradability, and eco-friendliness
We have elucidated the effects of anion-specific interactions on NCh by exposing NCh thin films to various electrolytes and measuring the change in film thickness by quartz crystal microgravimetry with dissipation (QCM-D)
After accounting for salt-induced changes in the solution medium, corrected dissipation energy values confirm that the Sauerbrey condition is satisfied for all the tests performed here, in which case the corrected change in frequency directly relates to changes in NCh film thickness
Summary
The field of bio-derived materials is rapidly developing due to their important attributes, such as sustainability, biodegradability, and eco-friendliness. NCh forms uniform and stable layers on gold resonators, used as supports in QCM-D experiments This analytical technique is well-suited for elucidating surface interactions given its sensitivity to changes in water coupling, as measured by changes in resonance frequency and energy dissipation. The NCh stock suspension was diluted to 0.01 wt % and vigorously stirred prior to spin coating onto gold-coated quartz sensors (QSense, Gothenburg, Sweden) Before this process, the gold AT-cut quartz crystal sensors (measuring 14 mm in diameter) were cleaned by immersion in 20 wt % NaOH(aq) solution for 30 s, followed by rinsing with DI water, drying with nitrogen gas, and exposure to UV/ ozone for 20 min. The value of D, defined as the inverse of the quality (Q) factor, is related to the inverse of the oscillatory decay time
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