Silk threads have been used in the textile industry for centuries. However, silk is also a promising base for the design of new materials with applications in areas such as biomaterials, optics, photonics, and electronics.

Rui F. P. Pereira, Verónica de Zea Bermudez, University of Trás-os-Montes e Alto Douro, Vila Real, Portugal, and colleagues have developed polymer electrolytes (PEs) based on the protein silk fibroin (SF) and tested them in smart window prototypes.

The team used silkworm cocoons to produce silk fibers, which were dissolved in LiBr solution at 60 ºC to produce a silk fibroin solution. They synthesized a non-doped SF film and two Li⁺-doped films from the fibroin using LiTFSI (lithium bis(trifluoromethanesulfonyl)imide) and LiBF₄, respectively. Glycerol was added as a plasticizer, and the reactant solutions were cast onto petri dishes and dried at room temperature over 72 hours to give the desired films.

The transparent films were then used as polymer electrolytes in electrochromic smart windows, which can be darkened by applying a voltage. The proof-of-concept devices had very fast switching times and good stability and cyclability. According to the researchers, these results might help to find new design approaches for silk-based materials, especially in energy-related applications.

• Smart windows prepared from Bombyx mori silk,
  Rui F. P. Pereira, Franciani Sentanin, Agnieszka Pawlicka, Cristina Gonçalves, Manuela Silva, Verónica Bermudez,
  ChemElectroChem 2016.
  DOI: 10.1002/celc.201600095