Broadband dielectric response of silk Fibroin/BaTiO3 composites: Influence of nanoparticle size and concentration

In order to advance towards more sustainable electronics generation, natural polymers with tailored dielectric response are essential. In this search, the combination of bio-based materials with active fillers in composite form, suppose one of the most viable alternatives. To achieve it, this work has explored the ability to control dielectric response of Silk Fibroin, a protein polymer by its combination with ceramic barium titanate (BaTiO3) nanoparticles. Both the effect of filler concentration (0, 5, 10, 20 and 40 wt%) and size (100 and 200 nm) has been studied in composites processed by easily scalable techniques. Samples with a homogeneous distribution of nanoparticles have been obtained. Dielectric relaxation processes assessed by broadband dielectric relaxation spectroscopy (BDS) in wide frequency (0.1 Hz–1 MHz) and temperature ranges (- 40 to 220 °C), revealed a dielectric constant increasing with filler content and decreasing with filler size, ranging from 4.4 for SF up to 142 for the SF/BaTiO3 composite with 40 wt %, at room temperature and 1 kHz. Two relaxations processes are observed, the β-relaxation and the conductivity relaxation, both with temperature-dependent behaviour. The activation energy of the conductivity process decreases with increasing nanoparticle content and decreasing size. A Maxwell-Wagner-Sillar process related to the interface between the silk fibroin matrix and the BaTiO3 nanoparticles was also identified.The authors thank the FCT (Fundacao para a Ciencia e Tecnologia) for financial support under the framework of Strategic Funding grants UID/FIS/04650/2019, and UID/EEA/04436/2019; and project PTDC/FIS-MAC/28157/2017. The author also thanks the FCT for financial support under grant SFRH/BPD/112547/2015 and Investigator FCT Contract 2020.04028.CEECIND (C.M.C.) as well POCH and European Union. Financial support from the Spanish Ministry of Science and Innovation (MCINN, Agencia Estatal de Investigacion) through the project RTI2018-097862-B-C21 and MAT2016-76039-C4-3-R (AEI/FEDER, UE) (including the FEDER financial support) and from the Basque Government Industry and Education Departments under the ELKARTEK, HAZITEK and PIBA (PIBA-2018-06) programs, respectively, are acknowledged. CIBER-BBN is an initiative funded by the VI National R&D&I Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program. CIBER Actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund