Transparent polymer nanocomposites: An overview on their synthesis and advanced properties

Abstract

Since the last decade, there has been an increasing demand for the design of more advanced functional materials. The integration of inorganic nanoparticles to polymer matrices is a powerful tool to confer their fascinating and complementary properties to the polymer materials. Among the different polymer nanocomposites, transparent nanocomposites are of particular interest due to their significance in a wide range of applications. To achieve a high level of transparency in the nanocomposites, it is necessary to minimize the aggregation of the nanoparticles that induce significant light scattering and thus hamper the application for transparent materials. The basic concepts of light scattering, the refractive index modulation and the methods to characterize the transparency of nanocomposites are provided to introduce this review. The fabrication of the transparent nanocomposites has been the subject of many efforts to develop methods to limit aggregation. To address this challenge, several methods have been implemented to control the polymerization process, the nanoparticle synthesis, and the polymer-nanoparticle interface together with the polymer casting or processing. The main methodologies developed to fabricate transparent nanocomposites are discussed according to four main categories: the blending of nanoparticles and polymer; the in-situ polymerization in the presence of pre-formed nanoparticles; the in-situ nanoparticle synthesis in a pre-formed polymer matrix; and finally the simultaneous polymerization and in-situ nanoparticle synthesis. The few studies dealing with casting of polymer solution loaded with core-shell nanoparticles are also discussed. In light of the literature on polymer nanocomposites, this review focuses on transparent nanocomposites with special attention given to the level of transparency and how this transparency is assessed for each study claiming transparency of the nanocomposite. For each class of nanocomposites, it is of great importance to provide an overview of the different level of transparency according to the thickness of the polymer material. The second part of the review provides a thorough overview of the properties investigated in transparent nanocomposites with attention paid to the characterization of transparency. The transparent nanocomposites were described according to the targeted properties which are primarily the improvement of mechanical properties, thermal stability, barrier properties, magnetic properties and the optical properties. The optical properties have been the most thoroughly investigated due to the myriad inorganic nanoparticles exhibiting an excellent wide range of optical properties. Thus, the present review also describes the polymer/nanoparticle systems designed for the fabrication of transparent polymer nanocomposites with advanced optical properties: UV or IR-filtering properties, photoluminescence, ability to produce extreme refractive index, dichroism or non-linear optical properties.