Control temperature fluctuations with replaceable spin-crossover material

a) Schematic of the behavior of SCO materials during the day-night cycle. b) Schematic of work of SCO material under solar radiation. When the weather is hot, and the material is in the HS (white) state, light is reflected and the increase in room temperature is controlled. In contrast, under cold temperatures, the material exhibits the LS state (pink), so more wavelengths are absorbed and the room gets hotter. c) Illustration of rotational transition under external stimuli. Credit: Advanced Science (2022). DOI: 10.1002/advs.202202253

Reducing the heat island effect through thermal regulation mechanisms on building elements can improve human thermal comfort and the living environment in urban areas. Passive thermal control systems that combine with roofs, windows or walls, and operate without the need for electricity, are an energy efficient and environmentally friendly solution.

Phase change materials minimize temperature fluctuations through the use of latent heat, but have some limitations. The application of this technique has resulted in cooling during the day and night. Therefore, research on new materials that reduce temperature fluctuations in both directions is needed.

The researchers led by Dr. José Sánchez-Costa and Dr. Ana Espinosa at IMDEA Nanociencia has demonstrated that molecular materials can be applied for thermal regulation purposes in a new approach. In their latest work, published in Advanced Sciencethe group tested a molecular-based coordination polymer embedded in a plastic matrix against several heating-cooling cycles.

They observed concurrent phase transitions and color changes, from pink to white, which produced a cooling effect on other thermochromic materials. The measured temperatures show that the heated material is able to dissipate heat more efficiently through two effects: absorption of energy that triggers a phase transition and optical reflection as the color changes to white—reflecting more energy. Furthermore, the cooled material (pink) produces a temperature drop damper due to desorption of heat generated at the phase transition. This means lower temperature fluctuations during heating and cooling cycles.

temperature vs. exposure time with on-off solar cycle. Credit: Advanced Science

The spin-crossover molecular material is very stable on the cycle; in this study, up to 40 cycles were performed, yielding similar results. This versatile material can be designed for specific properties, such as transition temperature and thermal hysteresis.

In this study, the researchers demonstrated that the heat generated by the sun is sufficient to produce spin transitions in spin-crossover materials. This, in turn, causes a cooling effect due to the increased light reflection resulting from the color change and energy absorption associated with the spin transition. Therefore, spin-crossover molecular materials can be used to reduce temperature fluctuations, and have the potential to be implemented in passive temperature control elements in buildings.

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Reducing energy consumption: Researchers develop test system for passive cooling materials

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Further information:
Esther Resines-Urien et al, Thermochromic Effects and Concurrent Phase Changes in Switchable Spin Crossover Materials for Efficient Passive Control of Day and Night Temperature Fluctuations, Advanced Science (2022). DOI: 10.1002/advs.202202253

Provided by IMDEA Nanociencia

Quote: Temperature fluctuation control with replaceable spin-crossover material (2022, 22 July) retrieved 23 July 2022 from https://phys.org/news/2022-07-temperature-fluctuation-switchable-spin-crossover-material.html

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