Ultrathin films made from renewable resources have become an area of increasing interest for materials scientists as they provide an interesting platform for technological advancements in areas including biosensors, transmitters and optoelectronic materials. For all these types of applications, the stability of the matrix to atmospheric conditions is critical to ensure predictable in-service performance. In this study, the swelling behavior of cellulose nanocrystal (CNC) thin films has been investigated using several analytical techniques; ellipsometric porosimetry, quartz crystal microbalance with dissipation (QCM-D), x-ray reflectivity (XRR) and infrared reflection absorption spectroscopy (IRRAS). In contrast to what was expected, the results demonstrated that CNC networks supported on a silica substrate showed significant swelling upon the uptake of water vapor. CNCs in themselves are not able to swell upon exposure to water vapor as it is unable to penetrate into the crystalline structure thus has no effect on crystal dimensions. Our measurements clearly establish that thin film CNC networks are responsive to water vapor as they exhibit extensive swelling as a function of relative humidity. Hypothetically, swelling of these films results from flexibility within the nanocrystal network as water vapor is believed to condense in the voids between the CNCs generating capillary pressure that is significant enough to allow movement of the individual CNCs, resulting in the observed swelling.

Flexibility of cellulose nanocrystal networks in response to water vapor

249th National Meeting (2015)

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