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Transparent and UV‐Reflective Photonic Films and Supraballs Composed of Hollow Silica Nanospheres
Author(s) -
Lim Yirang,
Lee SeungHeon,
Li Yan,
Kim SeungHyun,
Kang Tae Hui,
Suh Yung Doug,
Lee Soojin,
Kim Yongjin,
Yi GiRa
Publication year - 2020
Publication title -
particle and particle systems characterization
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.877
H-Index - 56
eISSN - 1521-4117
pISSN - 0934-0866
DOI - 10.1002/ppsc.201900405
Subject(s) - materials science , refractive index , visible spectrum , polymer , reflection (computer programming) , ethylene glycol , optics , wavelength , colloidal silica , high refractive index polymer , optoelectronics , nanotechnology , chemical engineering , composite material , physics , computer science , engineering , programming language , coating
For an optically transparent, UV‐reflective film, hollow silica nanospheres smaller than the visible wavelength (<λ vis ) are prepared and assembled into colloidal glasses, of which interstices are then backfilled with a polymer. The polymer refractive index is matched with the silica shell to minimize backscattering in the visible range, and the average distance between the hollow silica particles is adjusted by tuning the shell thickness to satisfy the interference resonance condition for a UV selective reflection. The resulting composite film shows a strong UV reflection as expected, but it is translucent in visible light due to non‐negligible backscattering, which may be caused by large defects or fluctuation of the particle concentration. In order to avoid such backscattering, another polymer is introduced of which the refractive index is matched with the average refractive index of the hollow nanospheres. This allows an optically transparent film that selectively reflects the UV light. Furthermore, spherical aggregates of hollow silica nanospheres called “supraballs” are prepared and their average refractive index is matched with a solvent by adjusting the mixture ratio of water and ethylene glycol, which yields an optically transparent solution, selectively reflecting UV.