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Mechano-thermo-chromic device with supersaturated salt hydrate crystal phase change

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Science Advances  26 Jul 2019:
Vol. 5, no. 7, eaav4916
DOI: 10.1126/sciadv.aav4916
  • Fig. 1 Operation mechanism and scanning electron microscopy images of MTC device.

    (A) Solubility graph at different temperature for sodium acetate anhydrous (CH3COONa, red line) and sodium acetate trihydrate (CH3COONa·3H2O, black line) where the solid lines indicate a saturated state. Insets show the digital pictures of MTC glass for various phase conditions. The right graph shows the general process of MTC, which is composed of the mechanochromic process and the thermochromic process. (B) The microscopic surface morphology of sodium acetate crystal with (i) low- and (ii) high-magnification scanning electron microscopy (SEM) images. The red dotted box exhibits the boundary of the crystal and the yellow dotted box shows the surface, which has an irregular vertically stacked structure.

  • Fig. 2 Fabrication process and optical property characterization of MTC device.

    (A) The fabrication process of MTC device that consisted of a chamber for sodium acetate solution and the transparent microheater prepared by acid-assisted laser sintering of Cu nanoparticle paste. (B) The digital images and (C) UV-vis analysis of the transparency shift after phase change for each chamber thickness (photo credit: Hyunmin Cho and Jinhyeong Kwon, Seoul National University).

  • Fig. 3 Transient thermal response characterization of the MTC device.

    (A) The optical characteristics change during the phase change of the sodium acetate crystal for each chamber at 70°C heating. The background picture used is courtesy of J.K. (B) The transient temperature measurement and corresponding infrared (IR) camera images for the electrothermal performance and temperature distribution of the transparent microheater depending on the thickness of each chamber.

  • Fig. 4 Real-time optical and thermal response during the reversible phase transition.

    (A) Spectral transmittance of MTC devices integrated with the 2-mm-thick chamber (chamber 2) and the transparent microheater depicts the supersaturated liquid phase (black line) and the crystalized solid phase (red line). (B) Cyclic operation test for the durability and reliability of the MTC device. Temperature (black line) and transmittance (red line) changes were recorded along with the corresponding digital images. (C) Real-time variation of the temperature and transmittance during the transparent microheater operation for phase change to liquid. (D) Real-time measurement and calculation of temperature and transmission change during the exothermic phase change of sodium acetate crystallization. (E) A relationship between temperature and transmittance of the MTC device during the one-cycle operation. A sharp decline (black line) of transmittance by mechanical stimulus along with exothermic reaction. Natural cooling (green line) after exothermal reaction with remaining low transparency. Phase transition to liquid (red line) by electrothermal heat from a microheater. Natural cooling (blue line) after heating with the remaining liquid state and high transmittance. (F) Digital picture and IR camera image during the sodium acetate crystal growth after mechanical stimulation impact at the right top corner of the sample (red dot).

  • Fig. 5 Active smart window application under UV irradiation.

    (A) A miniaturized mock-up demonstration with small MTC device–installed window and control units and (B) corresponding diagram. (C) Real-time digital images during the operation of the MTC system. The irradiation of UV light works as trigger for the sodium acetate crystallization and corresponding optical property change. The transparent microheater was turned on for phase transition from solid to liquid. See also movies S1 and S2 (photo credit: Hyunmin Cho and Jinhyeong Kwon, Seoul National University).

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/5/7/eaav4916/DC1

    Table S1. Simple comparison of the characteristics for various smart window technologies.

    Table S2. Experiment conditions and results regarding mechanical stimulus and crystallization.

    Table S3. Digital images for the sodium acetate crystallization regarding two cases of applied mechanical stimulation.

    Table S4. Various factors and conditions for the calculation of exothermic heat generation.

    Fig. S1. Mechanical stimulus schematic, crystallization probability, and volume change for crystallization.

    Fig. S2. The optical and thermal behavior analysis of MTC device and microheater.

    Fig. S3. Cyclic durability test and real-time measure system of transmittance.

    Fig. S4. A pendulum impact test for mechanical external stimulus.

    Fig. S5. The logic flow chart for smart glass system integrated with MTC device and control units.

    Movie S1. The real-time operation of smart glass system by sodium acetate crystallization with mechanical perturbation when the UV sensor detected UV light.

    Movie S2. The real-time operation of smart glass system by sodium acetate phase change to saturated liquid state.

  • Supplementary Materials

    The PDF file includes:

    • Table S1. Simple comparison of the characteristics for various smart window technologies.
    • Table S2. Experiment conditions and results regarding mechanical stimulus and crystallization.
    • Table S3. Digital images for the sodium acetate crystallization regarding two cases of applied mechanical stimulation.
    • Table S4. Various factors and conditions for the calculation of exothermic heat generation.
    • Fig. S1. Mechanical stimulus schematic, crystallization probability, and volume change for crystallization.
    • Fig. S2. The optical and thermal behavior analysis of MTC device and microheater.
    • Fig. S3. Cyclic durability test and real-time measure system of transmittance.
    • Fig. S4. A pendulum impact test for mechanical external stimulus.
    • Fig. S5. The logic flow chart for smart glass system integrated with MTC device and control units.
    • Legends for movies S1 and S2

    Download PDF

    Other Supplementary Material for this manuscript includes the following:

    • Movie S1 (.mp4 format). The real-time operation of smart glass system by sodium acetate crystallization with mechanical perturbation when the UV sensor detected UV light.
    • Movie S2 (.mp4 format). The real-time operation of smart glass system by sodium acetate phase change to saturated liquid state.

    Files in this Data Supplement:

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