Terahertz complex conductivity of cellulose nanocrystal based composite films controlled with PEDOT:PSS blending ratio
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ORIGINAL RESEARCH
Terahertz complex conductivity of cellulose nanocrystal based composite films controlled with PEDOT:PSS blending ratio Takeya Unuma . Omou Kobayashi . Shoya Kotaka . Rajesh Koppolu . Martti Toivakka . Jarkko J. Saarinen
Received: 8 April 2020 / Accepted: 15 September 2020 Ó Springer Nature B.V. 2020
Abstract We investigate the terahertz complex conductivity spectra of cellulose nanocrystal (CNC) based composite films fabricated with different blending ratios of the conducting polymer poly(3,4ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and without/with glycerol additive. A partially localized nature of carriers in the composite is clearly seen in the obtained spectral shapes of
complex conductivity and is well described by an extended Drude model. We find that the carriers become denser and less localized with increasing PEDOT:PSS blending ratio and that the addition of glycerol to the composite is efficacious in enhancing carrier delocalization as well as mechanical flexibility.
T. Unuma (&) O. Kobayashi S. Kotaka Department of Electrical, Electronics and Information Engineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2188, Japan e-mail: [email protected] R. Koppolu M. Toivakka Laboratory of Natural Materials Technology, Center for ˚ bo Akademi University, Functional Materials, A ˚ bo/Turku, Finland Porthansgatan 3, 20500 A J. J. Saarinen Department of Chemistry, University of Eastern Finland, P.O. Box 111, 80101 Joensuu, Finland e-mail: [email protected]
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Cellulose
Graphic abstract
Keywords Cellulose nanocrystals Conducting polymers Composite films Terahertz spectroscopy Charge transport
Introduction Nanocellulose is a sustainable biomaterial with optical transparency, mechanical flexibility, and surface smoothness (Eichhorn et al. 2010; Klemm et al. 2011; Isogai et al. 2011; Moon et al. 2011; Dufresne 2013). Both amorphous cellulose nanofibrils (CNFs) and purely crystalline cellulose nanocrystals (CNCs) provided with conductivity (Shi et al. 2013) have found a wide variety of organic optoelectronics applications (Hu et al. 2013; Huang et al. 2013; Koga et al. 2013; Zhou et al. 2013; Fujisaki et al. 2014; Jung et al. 2015; Nogi et al. 2015). Very recently, CNC based nanocomposites have been used as antibacterial fluorescent films functionalized with quantum dots (Xie et al. 2019) and as cryogel structures with high specific surface area (Darpentigny et al. 2020). Furthermore, there are a few studies on the optoelectronic response of nanocellulose in the terahertz (THz) region (Andrianov et al. 2015; Carnio et al. 2016; Elfwing et al. 2018; Unuma et al. 2019), whose importance for science and technology has rapidly increased over the last two decades (Ferguson and Zhang 2002; Tonouchi 2007; Lloyd-Hughes and Jeon 2012). These studies suggest that different states of both nanocellulose itself and introduced carriers are uniquely reflected in THz spectral shapes and also provide m
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