Open Access

ARTICLE

Formation of Highly Oriented Cellulose Nanocrystal Films by Spin Coating Film from Aqueous Suspensions

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1 Department of Chemical and Biomolecular Engineering, Clemson University, Clemson, South Carolina, USA 29634
2 Department of Material Science & Engineering, Clemson University, Clemson, South Carolina, USA 29634

*Corresponding author:

Journal of Renewable Materials 2016, 4(5), 377-387. https://doi.org/10.7569/JRM.2016.634131

Abstract

Spin coating was used to cast a uniform film of cellulose nanocrystals with low surface roughness and variable thickness as a function of operational parameters that include rotational speed and dispense suspension concentration. The film thickness was controllable from 40 nm up to 1 μm with surface roughness an order of magnitude less than blade-coating methods. The degree of radial orientation was qualitatively assessed and shown to be variable with processing parameters. Under specific processing conditions, the formation of striation patterns was observed and associated with film drying instability. The striation patterns are periodic in nature where the wavelength and amplitude are controllable to a certain degree with wetting film concentration and rotational speed. The striation patterns possess ordered, oriented nanorods, which exist as both rippled ring-like structures and radial ridges along the shear direction. There is potential to employ these rippled structures as low-cost manufacturing of ordered materials, device platforms, or optical components such as diffraction gratings. Mechanical properties of the films were measured by nanoindentation. The maximum elastic modulus of the films was 8.3 GPa and the maximum hardness was 322 MPa. A post-drying heat treatment (80 °C) was employed and resulted in a 17% increase in modulus and 35% increase in hardness, which is attributed to the formation of an enhanced intermolecular hydrogen bonding network between nanocrystals with removal of bound water.

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Keywords

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