Optically switchable natural silk

Journal Article · Mon Mar 02 00:00:00 EST 2015 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4913912· OSTI ID:22412782

Krasnov, Igor; Müller, Martin ^[1]; Krekiehn, Nicolai R.; Jung, Ulrich; Magnussen, Olaf M. ^[1]; Krywka, Christina ^[2]; Zillohu, Ahnaf U.; Strunskus, Thomas ^[3]; Elbahri, Mady ^[2]

---

1. Institut für Experimentelle und Angewandte Physik, Universität Kiel, D-24098 Kiel (Germany)
2. Institute of Materials Research, Helmholtz-Zentrum Geesthacht (HZG), D-21502 Geesthacht (Germany)
3. Institut für Materialwissenschaft, Universität Kiel, D-24098 Kiel (Germany)

An optically active bio-material is created by blending natural silk fibers with photoisomerizable chromophore molecules—azobenzenebromide (AzBr). The material converts the energy of unpolarized light directly into mechanical work with a well-defined direction of action. The feasibility of the idea to produce optically driven microsized actuators on the basis of bio-material (silk) is proven. The switching behavior of the embedded AzBr molecules was studied in terms of UV/Vis spectroscopy. To test the opto-mechanical properties of the modified fibers and the structural changes they undergo upon optically induced switching, single fiber X-ray diffraction with a micron-sized synchrotron radiation beam was combined in situ with optical switching as well as with mechanical testing and monitoring. The crystalline regions of silk are not modified by the presence of the guest molecules, hence occupy only the amorphous part of the fibers. It is shown that chromophore molecules embedded into fibers can be reversibly switched between the trans and cis conformation by illumination with light of defined wavelengths. The host fibers respond to this switching with a variation of the internal stress. The amplitude of the mechanical response is independent of the applied external stress and its characteristic time is shorter than the relaxation time of the usual mechanical response of silk.

• OSTI ID: 22412782
• Journal Information: Applied Physics Letters, Vol. 106, Issue 9; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 0003-6951
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ACTUATORS
DIRECT ENERGY CONVERSION
FIBERS
ILLUMINANCE
MECHANICAL PROPERTIES
MOLECULES
MONITORING
ORGANIC BROMINE COMPOUNDS
RELAXATION TIME
RESIDUAL STRESSES
SPECTROSCOPY
SYNCHROTRON RADIATION
VARIATIONS
VISIBLE RADIATION
X-RAY DIFFRACTION