The Effect of Ormosil Matrix Composition and Alkaline Earth Metal Doping on the Photochromic Response of Ormosil-Phosphotungstate Films

Elias P Ferreira Neto,Jean M S C Yabarrena,Julia C Noveletto,Mateus B Simões,Ubirajara P Rodrigues Filho,Sajjad Ullah

doi:10.5935/0103-5053.20150282

Elias P Ferreira Neto, Jean M S C Yabarrena + Show 4 more

Open Access

https://doi.org/10.5935/0103-5053.20150282

Copy DOI

Abstract

In this study, polyoxometallate based hybrid photochromic materials were prepared by incorporating phosphotungstate anion, PW12O403−, (PW) in hybrid tetraethyl orthosilicate and (3-glycidyloxypropyl)trimethoxysilane TEOS-GPTMS derived organomodified silicates (Ormosil) matrices by sol-gel method and the resulting materials were used to prepare multilayer films by dip-coating method. The effect of alkaline earth metal cations doping and matrix composition (%GPTMS) on the photochromic response of the hybrid films was studied in details. GPTMS, after undergoing ring opening reaction, leads to the formation of chelating sites (diol and ether functionalities) which helps in anchoring of cations, which in turn interacts with phosphotungstate anions and favors their incorporation in the hybrid films. For a fixed concentration of GPTMS, the cation-phosphotungstate electrostatic interaction and hence the photochromic response of the films follow the order Mg2+ < Ca2+ < Sr2+ < Ba2+, thereby, indicating that larger cations interact more strongly with the heteropolyanions. The presence of these cations and GPTMS concomitantly leads to increased incorporation of phosphotungstic acid hydrate (HPW) in the films, resulting in a significant enhancement of the photochromic response.

Highlights

We report the preparation of tetraethyl orthosilicate (TEOS)-GPTMS-phosphotungstic acid hydrate (HPW) hybrid films doped with alkaline-earth divalent cations (Mg2+, Ca2+, Sr2+ and Ba2+)
Photochromic hybrid Ormosilphosphotungstate materials were prepared using sol-gel route and the resulting hybrid materials were immobilized as multilayer films on glass substrate using dip-coating technique
The presence of GPTMS and alkaline earth metal cations leads to a significant enhancement of the photochromic response of the films by increasing the amount of phosphotungstate anions incorporated in the films

Summary

Introduction

Photochromic materials present interesting properties related to light-induced changes in optical absorption leading to reversible coloration/discoloration upon exposure to light.[1,2,3] Great attention has been dedicated to research on photochromic materials due to their potential applications in optical lenses, smart windows, optical memory devices UV sensors, counterfeit devices, among others.[2,3,4,5,6,7,8]Polyoxometalates (POMs) are discrete metal-oxide nanoclusters[9,10] which exhibit promising photochromic behavior. A systematic study of the role of hybrid matrix composition and the presence of the doping cations in the film assembly (POM incorporation) and photochromic response of the resulting Ormosil‐polyoxometallate coatings is presented.

Results

Conclusion