Variable solar control using thermotropic core/shell particles

• Published in: Solar energy materials and solar cells Vol. 93; no. 9; pp. 1510 - 1517
• Main Authors: Muehling, Olaf, Seeboth, Arno, Haeusler, Tobias, Ruhmann, Ralf, Potechius, Elvira, Vetter, Renate
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.09.2009; Elsevier
• Subjects: Applied sciences; Core/shell particles; Efficiency; Energy; Exact sciences and technology; Miniemulsion polymerization; Miscellaneous; Natural energy; Overheating protection; Particle size; Particulates; Polymers; Q1; Smart windows; solar cells; Solar energy; Spectroscopy; sun; Sun protection glazing; Thermotropic materials; transmittance; Miniemulsion polymerization; Sun protection glazing; Core/shell particles; Thermotropic materials; Overheating protection; Smart windows; Costs; Particle size; Sun protection; Glass; Polymerization; Solar glazing; Thermotropic crystals; Transmittance; Optical properties; Curing; Resins; Ultraviolet visible spectrometry
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2009.03.029

Subject of our recent investigations is the utilization of a reversible thermotropic material for a self-regulating sun protection glazing that controls the solar energy input in order to avoid overheating. Based on the well-established UV curing technology for laminated glass a superior thermotropic material with tunable switching characteristics and of low material costs was developed. The polymer layer contains core/shell particles homogeneously dispersed in a UV-cured resin. The particle core in turn consists of an n-alkane mixture that is responsible for the temperature-induced clear/opaque switching. To obtain particles of well-defined size and with a narrow size distribution, the miniemulsion polymerization technique was used. The visible and solar optical properties (normal–normal, normal–hemispherical, and normal–diffuse transmittance) in the off (clear) and in the on state (opaque) were determined by UV/Vis/NIR spectroscopy. Samples containing particles of high median diameter (>800 nm) primarily scatter in the forward direction. However, with smaller particles (300–600 nm) a higher backscattering (reflection) efficiency was achieved. The largest difference in the normal–hemispherical transmittance could be found with a particle amount of 6% and a median scattering domain diameter of ∼380 nm.