Dynamic Changes in Structural Color of a Lamellar Block Copolymer Photonic Gel during Solvent Evaporation

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• 作者：Wonmok Lee ; Jongseung Yoon ; Edwin L. Thomas ; Hyunjung Lee
• 刊名：Macromolecules
• 出版年：2013
• 出版时间：August 27, 2013
• 年：2013
• 卷：46
• 期：16
• 页码：6528-6532
• 全文大小：377K
• 年卷期：v.46,no.16(August 27, 2013)
• ISSN：1520-5835

文摘

A high molecular weight, lamellar block copolymer (BCP) can exhibit a photonic stop band in the visible range of wavelengths due to the one-dimensional periodic dielectric layer structure. After dissolving a high molecular weight BCP in a neutral solvent, solvent evaporation causes microphase separation, forming a so-called 鈥減hotonic gel鈥?at a quite low polymer concentration (10 wt %). Moreover, by allowing the solvent to further evaporate, the reflected color can be tuned over the entire range of the visible spectrum. Here, a polystyrene鈥損olyisoprene diblock (PS-b-PI) is dissolved in cumene, and the solution was placed between two glass substrates. The radial concentration gradient during slow evaporation of the cumene generates a 鈥渞ainbow-like鈥?set of reflected colors from the photonic gel. Based on local measurement of the reflectivity along the radial direction of the photonic gel, the radial solvent composition was calculated and the experimentally observed reflectivity was compared to results simulated using the transfer matrix method. Balsara鈥檚 scaling law for the lamellar period versus polymer concentration was adapted for the simulation of the concentration profile, which showed a reasonable agreement with a previous theoretical calculation. Compared to the simulated spectra, experimentally obtained reflectance spectra exhibited weaker peak reflectivity and additional peak broadening due to lamellar misorientation and decrease of the average grain size during solvent evaporation.