I am looking for other photosensitive materials that change state, but produce significant physical distortion.
Silver halide crystals, for example, has a photographic-and unique photochemical qualities, but no significant change in physical presentation.
However, Azobenzene is noted as being a material that undergoes photo-isomerization due to light, producing molecular level unfolding or motion. The witnessed isomerization has also been demonstrated at a bulk or meso-scopic scale to lead to larger length motion on scales of inches through the folding and unfolding of origami like structures. A thin film of azobenzene was made to bend and unbend by exposing it to polarized light. The direction of the macroscopic motion could be controlled by the polarization direction, or wavelength. The bending occurred because the free surface of the material contracted more than the inside of the thin film (due to absorption of laser light as it passes through the film).
I am interested if there are other unique photo-mechanical compounds (or chemical-photon interaction processes) that exhibit similar or increased bulk strain behaviors.
Here are photo-responsive fibers mentioned.
https://phys.org/news/2015-12-hybrid-material-future-potential-4d-printed.html
Other materials:
http://physicsworld.com/cws/article/news/2016/sep/08/light-pushes-liquid-uphill
https://phys.org/news/2016-04-liquid-marbles-laser-video.html
Regards,
Joachim
Also, some new ferroelectrics[1,2] and other materials like chameleon pigments[3] .
1. Structure, Ferroelectric and Photoluminescence Properties of Eu-Doped CaBi4Ti4O15 Multifunctional Ceramics http://link.springer.com/article/10.1007%2Fs11664-015-3730-8
Magnetization-induced enhancement of photoluminescence in core-shell CoFe2O4@YVO4:Eu3+ composite http://aip.scitation.org/doi/10.1063/1.4837659
2. apart to classical liquid-crystal displays (LCD) See: Electrically modulated photoluminescence in ferroelectric liquid crystal https://arxiv.org/pdf/1212.6514v1.pdf
3. Keywords: chameleon, holographic pigments e.g. http://solarcolordust.com/p/faq, Gallium http://solarcolordust.com/t/gallium---metal-that-melts-at-86f
I would suggest to look among new ferroelectric materials as this class of compounds can develop substantial strain when exposed to light. Ferroelectrics generally manifests strong interaction with light, but for efficient generation of mechanical distortion it is necessary to excite them through the bandgap, so it is worth to look for ferroelectrics with relatively small bandgap to match it with wavelenght of light. The main feature of these materials is permanent ferroelectric polarization associated with strong internal electric fields in ferroelectric domains. What is more, all ferroelectrics are also piezolectrics, what means that they exhibit strong coupling of mechanical strain with electric field. Piezolectric coefficient for these materials is typically very high. Mechanism of photomechanical effect can be as follows: when light excites carriers through the bandgap, the free carriers in conduction band can efectively screen internal electric fields (what modifies local equilibrium) and through the internal piezoelectric effect can lead to development of stress and in consequence to strain. Very interesting question is also timescale of mechanical strain development and relaxation of it. Light can produce significant mechanical distortion, but it can also decay ultrafast. So it depends on whether change is quasipermanent (stable) or not. Very interesting example which I extensively studied experimentally is multiferroic material bismuth ferrite (BFO).
Dear Mariusz Lejman,
in addition, an internal ideal lasing mechanism is need to manifest such a high (optical-electrical to mechanical) stress in classical ferroelectrics.
A metamaterial's based chameleon superstructure might be a proposal lasing mechanism for a high optical stress in photo-engineering of ferroelectrics.
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