Kinetics of Helix Untwisting in Photosensitive Cholesteric Polymer Mixtures: Influence of Molecular Mass and Ordered Phase Formation

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• 作者：Alexey Bobrovsky ; Natalia Boiko ; Valery Shibaev
• 刊名：Macromolecules
• 出版年：2006
• 出版时间：September 19, 2006
• 年：2006
• 卷：39
• 期：19
• 页码：6367 - 6370
• 全文大小：173K
• 年卷期：v.39,no.19(September 19, 2006)
• ISSN：1520-5835

文摘

Photooptical behavior of cholesteric mixtures based on two fractions of nematic polymer withdifferent molar masses containing chiral-photosensitive dopant with C=C double was studied. UV irradiation ofplanarly oriented films of the mixtures leads to E-Z photoisomerization of dopant, helix untwisting and shift ofselective light reflection peak to the longer wavelength spectral region. Kinetics of this process was studied atdifferent temperatures. It was shown that a relative rate of helix untwisting for the mixture with the high molarmass fraction (DP ~ 87) is 2 orders of magnitude less than for the mixture containing a low-molar-mass fraction(DP ~ 22), whereas the activation energies of the helix untwisting for both mixtures have almost the samevalues. The formation of the ordered TDK* phase during annealing of the blend at 50 C for 1 week completelyprevents the helix untwisting. This fact is worthy of attention because it provides a possibility of fixing a helicalstructure even at temperatures above the glass transition; this advantage makes this system promising for opticaldata recording and storage.