Ultrasound-induced change of microstructure and photochromic properties of polyacrylamide thin films containing a polyox
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Jiannian Yao Center for Molecular Science, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China (Received 19 August 2002; accepted 27 December 2002)
Novel photochromic nanocomposite thin films were prepared by entrapping polyoxometalate in a polyacrylamide matrix via the ultrasound technique. The ultrasound irradiation has a great effect on the microstructure and photochromic properties of the hybrid films. The polyoxometalate nanoparticles are finely dispersed in the polymer matrix after ultrasound treatment, instead of agglomeration in the unirradiated film with ultrasound. Consequently, the photochromic behaviors of the hybrid films can be controlled from irreversible heteropolybrown to reversible heteropolyblue by ultrasound. The influence of ultrasound on microstructure and photochromic properties is due to the sonochemical controlling interfacial interactions in the hybrid system.
I. INTRODUCTION
Polyoxometalates (POMs) have attracted increasing attention because of their special structures and properties.1 One of the most important properties of these metal oxide clusters is that they can accept electrons or protons to become mixed-valency colored species (heteropolyblue or heteropolybrown).2 But these kinds of materials are difficult to manipulate into practical devices, which make them far from achieving application. Nowadays, the synthesis and characterization of POM-based inorganic–organic polymer composites have received much intensive research since they combine unique properties of the two components. These novel materials, considered as innovative advanced materials, promise new applications in many fields such as optics, electronics, catalysis, mechanics, biology, etc.3–6 According to the nature of the interfacial interactions between two components, these advanced materials can be categorized into two distinct classes.7 In class I, organic and inorganic compounds are embedded and only weak bonds (hydrogen bonds, van der Waals, or electrostatic forces) give cohesion to the whole structure. In class II, two components are linked together via strong chemical
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Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 18, No. 3, Mar 2003
bonds. The microstructure potential properties of these materials certainly depend on the chemical nature of interfacial interactions and the synergy between these components. Therefore, it is important to design a novel hybrid system via varying the nature, extent, and accessibility of the inner interface.8 The hybrid proceeding is a complex process involving chain orientation, chemical reaction, and structure relaxation, as well as the change of interactions between molecular components. In other words, the relationship among the microstructure, properties of these nanocomposites, and chemical nature of their components is of considerable practical significance. In previous work, we have prepared a series of hybrid films through entrapping POM in polyacrylamide matrix via hydrogen bon
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