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Abstract
Minnesota is home to some of the greatest temperature ranges in the United States, with lows reaching below -40º Celsius and highs reaching nearly 40ºC. This results in higher than average spending on the heating and cooling of buildings. We have been investigating into responsive building materials to help address this. In particular, we have been studying a thermochromic paint that can capture solar energy and transfer it into the building as heat at low temperatures and reflect the energy at higher temperatures to keep the building cooler

Corbett, Alexis

Hall, Danielle

Sinko, John E

English

St. Cloud State University

IntroductionMinnesota is home to some of the greatest temperature ranges in the United States, with lows reaching below -40º Celsius and highs reaching nearly 40ºC. This results in higher than average spending on the heating and cooling of buildings. We have been investigating into responsive building materials to help address this. In particular, we have been studying a thermochromic paint that can capture solar energy and  transfer it into the building as heat at low temperatures and reflect the energy at higher temperatures to keep the building cooler. Thermochromic materials are materials that change color in response to their temperature. Leuco dyes in general have a clear phase and a colored phase, ours in particular is black at low temperatures and transparent at higher temperatures. We have paired it with a white paint to improve reflectance at these higher temperatures and are looking into finding a coating that will enhance the absorption at low temperatures without changing the reflectance when the paint is white.Variable Temperature Thermochromic Switching Under Varying IlluminationFigure 11: SEM imaging of the surface deposition of the fluoran with a scale for each image. The top left image is at 200x resolution, top right is at 500x, bottom left is at 2000x, and the bottom right image is at 18000x resolution.Figure 5: Diagram of Experimental SetupFigure 6: Picture of Experimental Setup[1] Surface Thermometer[2] Lamp[3] Spectrometer[4] Sample[5] Power Meter[6] DAQ UnitFigure 3: Diagram depicting spin coating processFigure 4: Upper Left – Old Lens and New Lens,Lower Left – Wet TC Sample, Right – Dry TC SampleFigure 10: Reflectance and angle data obtained Fall 2016Figure 1: On the left is what our compound looks like when black and is considered the ‘closed form’ of the molecule. On the right is the transparent ‘open form’ where one of the bonds connecting an oxygen atom and carbon atom has been broken. In these pictures oxygen atoms are red, carbon atoms are grey, and nitrogen atoms are blue. The hydrogen atoms have been omitted from these images for simplicities sake.Figure 2: The leuco dye we are using is micro-encapsulated with a ‘soup’ of other chemicals to facilitate the switch. Bottom right is melamine, which forms the capsules. Top left is hexadecanol, top right is methyl stearate and bottom left is butyl stearate, these three are the ‘soup’ surrounding the leuco dye molecule.References1.Akbari, H., Konopacki, S., & Pomerantz, M. (1999, May). Cooling energy savings potential of reflective roofs for residential and commercial buildings in the United States. Energy, 24(5), 391-407.2.Gentle, A.R., Aguilar, J.L.C., & Smith, G.B. (2011, July). Optimized cool roofs: Integrating albedo and thermal emittance with R-value. Solar Energy Materials & Solar Cells, 95(12), 3207-3215.3.Kanazawa K., Nakamura K., & Kobayashi N. (2014). High-Contrast Electroswitching of Emission and Coloration Based on Single-Molecular Fluoran Derivatives. J. Phys. Chem. A, 118(31), 6026-6033.4.Karlessi, T., & Santamouris, M. (2015). Improving the performance of thermochromic coatings with the use of UV and optical filters tested under accelerated aging conditions. Int. J. Low-Carbon Tech., 10(1), 45-61.5.Karlessi, T., Santamouris, M., Apostolakis, K., Synnefa, A., & Livada, I. (2009, April). Development and testing of thermochromic coatings for buildings and urban structures. Solar Energy, 83(4), 538-551.6.Li, S., Li, Y., Jiang, M., Ji, S., Luo, H., Gao, Y., & Jin, P. (2013, July). Preparation and characterization of self-supporting thermochromic films composed of VO2(M)@SiO2 Nanofibers. ACS Appl Mater Interfaces, 5(14), 6453-6457.7.LookChem. (n.d.). 7-Anilino-3-diethylamino-6-methyl fluoran. Retrieved August, 2, 2016, from http://www.lookchem.com/7-Anilino-3-diethylamino-6-methyl-fluoran/.8.Liu, P., Zhou, D., Wei, Y., Jiang, K., Wang, J., Zhang, L., Li, Q., & Fan, S. (2015). Load Characteristics of a Suspended Carbon Nanotube Film Heater and the Fabrication of a Fast-Response Thermochromic Display Prototype. ACS Nano, 9(4), 3753–3759.9.Mastrapostoli, E., Karlessi, T., Pantazaras, A., Kolokotsa, D., Gobakis, K., & Santamouris, M. (2014, February). On the cooling potential of cool roofs in cold climates: Use of cool fluorocarbon coatings to enhance the optical properties and the energy performance of industrial buildings. Energy and Buildings, 69, 417-425.10.Ma, Y., Zhu, B., & Wu, K. (2001). Preparation and solar reflectance spectra of chameleon-type building coatings. Solar Energy, 70(5), 417-422.11.openMaterials. (n.d.). thermochromic materials. openMaterials. Retrieved August, 1, 2016, from http://openmaterials.org/materials-101-thermochromic/.12.McCluney, W.R. (1994). Introduction to Radiometry and Photometry. Massachusetts. Artech House, INC.13.Orndorff, W.R., Gibbs, R.C., & Shapiro, C.V. (1928). THE ABSORPTION SPECTRA OF FLUORESCEIN, FLUORAN AND SOME RELATED COMPOUNDS. J. Am. Chem. Soc., 50(3), 819-828.14.van der Werff, L.C., Robinson, A.J., & Kyratzis, I.L. (2012). Combinatorial Approach for the Rapid Determination of Thermochromic Behavior of Binary and Ternary Cholesteric Liquid Crystalline Mixtures. ACS Comb. Sci., 14(11), 605-612.15.Wallach, D.F.H., Surgenor, D.M., Soderberg, J., & Delano, E. (1959, March). Preparation and Properties of 3,6-Dihydroxy-2,4-bis-[N-N-di-(carboxymethyl)-aminomethyl] fluoran. Anal. Chem., 31(3), 456-460.16.Zhu, J., Zhou, Y., Wang, B., Zheng, J., Ji, S., Yao, H., Luo, H., & Jin, P. (2015, December). Vanadium Dioxide Nanoparticle-based Thermochromic Smart Coating: High Luminous Transmittance, Excellent Solar Regulation Efficiency, and Near Room Temperature Phase Transition. ACS Appl Mater Interfaces, 7(50), 27796-27803.AcknowledgementsWe would like to thank the following for use ofequipment: St. Cloud State University, Dr. Sivaprakasam,Dr. Sinko, the ETS Department, the MechanicalEngineering Department, and the Physics and AstronomyDepartment. We would also like to thank William Julius,Meredith Rupp, Kevin, Tobi, and Nancy for work on thisproject. And, of course, we would like to extend anenormous thank you to our research advisor Dr. JohnSinko.Future workRight now there are two students working on this project, Alexis Corbett and Danielle Hall. Alexis is working on determining the durability of our material by looking at how many color change cycles it will take before the material loses 50% of its initial efficiency and by testing the extreme temperature tolerances to ensure that this is viable and efficient for our (Minnesota’s) temperature range. Danielle is working on determining how much light energy is successfully converted into thermal energy. The title of the project currently comes from her portion of the research as this is her graduating semester.Voltages ΔTbottom / ΔTsurface26 V 0.23 °C / 0.25 °C39 V 0.51 °C / 0.45 °C52 V 0.98 °C / 0.92 °C78 V 1.94 °C / 1.87 °C91 V 2.59 °C / 2.57 °C117 V 4.39 °C / 4.33 °CVoltages ΔTbottom / ΔTsurface26 V 0.21 °C / 0.24 °C39 V 0.56 °C / 0.45 °C52 V 0.88 °C / 0.62 °C78 V 1.74 °C / 1.66 °C91 V 2.44 °C / 2.69 °C117 V 3.90 °C / 3.59 °CVoltages ΔTbottom / ΔTsurface26 V 0.24 °C / 0.25 °C39 V 0.59 °C / 0.65 °C52 V 0.97 °C / 1.17 °C78 V 2.10 °C / 2.13 °C91 V 2.79 °C / 2.69 °C117 V 4.45 °C / 4.78 °CFigure 7:(Above) 30°C Transition Temperature CoatingFigure 8:(Above) 25°C Transition Temperature CoatingFigure 9: (Above) 20°C Transition Temperature CoatingModel for thermal rise of a one-dimensional coatingThe temperature difference between the illuminated coating only differs from the temperature of the environment by a few degrees Celsius. We expect conduction (and linear convection) to dominate heat losses. Proceeding with these assumptions, the heat flow balance in the material is given by:𝑑𝑄𝑑𝑡=𝑚𝑐𝑠𝑑𝑇𝑑𝑡= 𝐼 1 − 𝑅 𝐴 −𝑠𝐴𝐿𝑠𝑇 − 𝑇𝑠𝑠 −𝑎𝐴𝐿𝑎𝑇 − 𝑇𝑎Danielle Hall1,2, Alexis Corbett3,4, John E. Sinko1,31 Masters Program in Materials & Instrumentation, St. Cloud State University, St. Cloud, MN 563012 Department of Chemistry & Biochemistry, St. Cloud State University, St. Cloud, MN 563013 Department of Physics & Astronomy, St. Cloud State University, St. Cloud, MN 563014 Department of Mathematics and Statistics, St. Cloud State University, MN, 56301Figures 7-9:Top-bottom layer. Middle – surface. Bottom –change in temperature.The overall temperature model employed in this study is then:𝑇 𝑡 =𝑇𝑠𝑠(0)𝑇0 + 𝑡 + Δ𝑇 1 − 𝑒−𝑡𝑇 + 𝑡 + 𝑇𝑒−𝑡𝑓𝑜𝑟𝑡  00 < 𝑡 < 𝑡𝑓𝑡 > 𝑡𝑓So far, this model lacks time-dependent temperature reflectance switching; its inclusion would appear in the form R(T) in the above model; this will be the next step in evolving the model.

Variable Temperature Thermochromic Switching Under Varying Illumination

https://repository.stcloudstate.edu/cgi/viewcontent.cgi?article=1007&amp;context=scsu_huskiesshowcase

Variable Temperature Thermochromic Switching Under Varying Illumination

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