Terahertz complex conductivity of nanofibrillar cellulose-PEDOT:PSS composite films

We investigate the terahertz transmission through flexible composite films that contain nanofibrillar cellulose (NFC) and different blending percentages of the conductive polymer poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS). The real part of terahertz complex conductivity is found to decrease with decreasing frequency for each NFC composite film and to approach a finite positive value dependent on the PEDOT:PSS blending percentage in the limit of zero frequency. Both the real and imaginary parts of complex conductivity spectra can be fitted simultaneously with an extended Drude model that describes a partially localized nature of carriers. Our spectral analysis indicates that carriers in the NFC composite become denser and also less localized as the PEDOT:PSS blending percentage is increased. Graphical abstract