Preparation of epoxy-based hybrid films from an aqueous TiO₂ dispersion via solvent exchange and surface modification with n-octylphosphonic acid

Abstract

Transparent TiO₂/epoxy hybrid films with high refractive indices have been prepared from a 9-mass% aqueous TiO₂ (rutile form) dispersion by a combination of dispersion medium exchange and surface modification with n-octylphosphonic acid (OPA). The dispersion medium was exchanged from H₂O to N-methylformamide (NMF) by distilling off H₂O after the addition of NMF. The TiO₂ surface was then modified with OPA by heating at 80 °C for 24 h. IR and NMR spectra of the OPA-modified TiO₂ nanoparticles (NPs) revealed that the OPA moiety was grafted onto the surface of the TiO₂ NPs through Ti–O–P bonds. The resulting OPA-modified TiO₂ NPs were employed to prepare epoxy-based hybrid films possessing excellent transparency. The transmittance in the entire visible range (400–800 nm) of the hybrid film containing 66.3 mass% TiO₂ was above 94%. This hybrid film also exhibited the highest refractive index (n = 1.74), which represented a remarkable increase from that of the pure epoxy resin film (n = 1.51).

Keywords:

• epoxy resin
• titania
• high refractive index
• organic–inorganic hybrids

Acknowledgments

This work was financially supported in part by a Grant-in-Aid for Scientific Research on Innovative Areas ‘New Polymeric Materials Based on Element-Blocks (No. 2401)’ (24102002), and the Global COE program ‘Center for Practical Chemical Wisdom’ of the Ministry of Education, Culture, Sports, Science, and Technology, Japan. The authors thank TAYCA Co., Ltd for donating the aqueous TiO₂ dispersion. They also thank Daihachi Chemical Industry Co., Ltd for donating n-octylphosphonic acid and Daicel Chemical Co., Ltd for donating 3, 4-epoxy cyclohexyl-methyl-3′, 4′-epoxycyclohexylcarboxylate.