Abstract
Optical materials with high refractive index (n) have been rapidly improved because of urgent demands imposed by the development of advanced photonic and electronic devices such as solar cells, light emitting diodes (LED and Organic LED), optical lenses and filters, anti-reflection films, and optical adhesives. One successful method to obtain high refractive index materials is the blending of metal oxide nanoparticles such as TiO2 and ZrO2 with high n values of 2.1–2.7 into conventional polymers. However, these nanoparticles have a tendency to agglomerate by themselves in a conventional polymer matrix, due to the strong attractive forces between them. Therefore, there is a limitation in the blending amount of inorganic nanoparticles. In this paper, various hydrophilic polymers such as poly(N-hydroxyl acrylamide) (pHEAAm), poly(vinyl alcohol), poly(ethylene glycol), and poly(acrylic acid) were examined for preparation of high refractive index film based on titanium oxide nanoparticle (TiNP) dispersed polymer composite. The hydrogen bonding sites in these hydrophilic polymers would improve the dispersibility of inorganic nanoparticles in the polymer matrix. As a result, pHEAAm exhibited higher compatibility with titanium oxide nanoparticles (TiNPs) than other water-soluble polymers. Transparent hybrid films were prepared by mixing pHEAAm with TiNPs and drop casting the mixture onto a glass plate. The refractive indices of the films were in good agreement with calculated values. The compatibility of TiNPs with pHEAAm was dependent on the surface characteristics of TiNPs. TiNPs with the highest observed compatibility could be hybridized with pHEAAm at concentrations of up to 90 wt%, and the refractive index of the corresponding film reached 1.90. The high compatibility of TiNPs with pHEAAm may be related to the hydrophilicity and amide and hydroxyl moieties of pHEAAm, which cause hydrogen bond formation on the TiO2 surface. The obtained thin film was slightly yellow due to the color of the original TiNP dispersion; however, the transmittance of the film was higher than 80% in the wavelength range from 480 to 900 nm.
Highlights
High refractive index materials are required to improve the performance of eyeglass lenses, optical fibers, and optical devices, such as waveguide-based optical circuits, optical interference filters and mirrors, optical sensors, and solar cells [1,2]
The titanium oxide nanoparticle (TiNP) (TiNP-1, 2, and 3) used in this study were characterized by Dynamic light scattering (DLS), X-ray diffraction measurements (XRD), and transmittance electron microscopy (TEM) analyses (Figure 1)
TEM images of TiNPs indicated that all TiNPs were nano-sized particles, the morphologies were different
Summary
High refractive index materials are required to improve the performance of eyeglass lenses, optical fibers, and optical devices, such as waveguide-based optical circuits, optical interference filters and mirrors, optical sensors, and solar cells [1,2]. Poly(4-vinylbenzyl alcohol) was reported as a matrix polymer for titania NPs. The composites were prepared by in-site polymerization of 4-vinylbenzyl alcohol in the acid surface-modified TiO2 nanoparticles dispersion. We have reported a new method for fabrication of high refractive index materials based on simple blending of polymers and heteropoly acids [28,29]. In these cases, hydrophilic moieties of polymers such as carbonyl and hydroxyl groups exhibited high compatibility with heteropoly acids which were molecularly dispersed in the polymer matrix. The hydrophilic polymers are examined as a matrix for titania NPs, and the optical properties including refractive index of the obtained composites are evaluated
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