Elsevier

Applied Surface Science

Volume 257, Issue 8, 1 February 2011, Pages 3451-3454
Applied Surface Science

Silane effects on the surface morphology and abrasion resistance of transparent SiO2/UV-curable resin nano-composites

https://doi.org/10.1016/j.apsusc.2010.11.044Get rights and content

Abstract

Transparent ultraviolet curable nano-composite coatings consisting of nano-sized SiO2 and acrylate resin have been developed to improve the abrasion resistance of organic polymers. The nano-sized SiO2 particles were surface-modified using various amounts of 3-methacryloxypropyltrimethoxysilane. The 3-methacryloxypropyltrimethoxysilane concentration effects on the surface morphology and abrasion resistance of the transparent SiO2/ultraviolet-curable resin nano-composites were investigated using scanning electron microscopy, atomic force microscopy, and ultraviolet-visible spectrophotometer. The results showed that as the 3-methacryloxypropyltrimethoxysilane/SiO2 weight ratio increased from 0.2 to 0.6, the dispersion, compatibility and cross-linking density between the 3-methacryloxypropyltrimethoxysilane-modified SiO2 particles and acrylate resin were improved, leading to an increase in abrasion resistance. However, as the 3-methacryloxypropyltrimethoxysilane/SiO2 weight ratio was increased to 1.5, the additional 3-methacryloxypropyltrimethoxysilane may exceed that needed to fill the pores with the probability of SiO2 nano-particles existing on the coating surface was lower than that for samples with a 3-methacryloxypropyltrimethoxysilane/SiO2 weight ratio of 0.6. This produced a decrease in abrasion resistance.

Research highlights

▶ The surface microstructure for the transparent SiO2/UV-curable resin coatings with various MEMO concentrations was investigated. ▶ MEMO/SiO2 weight ratio increased from 0.2 to 0.6, the dispersion, compatibility and cross-linking density between the MEMO-modified SiO2 particles and acrylate resin were improved, leading to an increase in abrasion resistance. ▶ As the 3-methacryloxypropyltrimethoxysilane/SiO2 weight ratio was increased to 1.5, the additional MEMO may exceed that needed to fill the pores with the probability of SiO2 nano-particles existing on the coating surface was lower than that for samples with a MEMO/SiO2 weight ratio of 0.6. This produced a decrease in abrasion resistance.

Introduction

Hybrid organic-inorganic nano-composites have received significant interest in recent years due to their superior mechanical properties and strong increase in scratch and abrasion resistance in coating applications. It is well known that the addition of inorganic nano-particles, typically SiO2 or Al2O3, to radiation-curable acrylate can promote hardness and result in a strong increase in scratch and abrasion resistance in these coatings [1], [2], [3]. However, the inorganic nano-particles are very hydrophilic and cannot be dispersed directly in low-polar acrylate resins. The surface modification of nano-sized SiO2 particles with a coupling agent, 3-methacryloxypropyltrimethoxysilane (MEMO) in radiation-curable acrylate formulations, can offer superior performance, such as improved dispersibility, increased compatibility between SiO2 and acrylate monomers and adhesion strength between the SiO2 particles and polymer matrix due to silane molecule vinyl groups grafted onto the SiO2 surface, participating in acrylate monomer free radical polymerization [4], [5], [6].

The silane concentration employed in the solution during surface modification will affect the configuration of the silane added into the SiO2-resin nano-composites [7], [8]. The resulting silane configurations will in turn, affect the dispersion and rheological behaviors of the coating suspension and the microstructures and mechanical properties of the coatings. However, the relationship between the silane configurations, surface morphology and abrasion resistance of the SiO2-resin nano-composites has not been well understood.

This study examines the MEMO silane concentration effects on the surface morphology and abrasion resistance of transparent SiO2/UV-curable resin nano-composites using scanning electron microscopy, atomic force microscopy, and UV–vis spectrophotometer.

Section snippets

Experimental procedures

MEMO prehydrolysis (Degussa, AG) was conducted by gently mixing MEMO, deionized water and ethyl alcohol with MEMO:deionized water:ethyl alcohol = molar ratio of 1:2:1 for about 3 h. The nano-sized SiO2 (QS-102, Tokuyama; mean particle size: 15 nm; specific surface area: 200 m2/g) was first intensively stirred in n-isopropanol (Mallinckrodt Chem., 99.5%) using a magnetic stirrer at around 600–700 rpm for about 1–2 min, followed by ultra-sonication in an ice bath for 30 min. Samples were then mixed with

Results and discussion

Fig. 1 shows AFM pictures of the coatings with various MEMO concentrations. For the 0.6C sample the surface microstructure shows a clearly visible outline of dispersed SiO2 nano-particles with a particle size close to the primary particle size. As the MEMO/SiO2 was increased to 1.0, the appearance of SiO2 nano-particles was still visible, but the particle size appeared larger than that of the primary particle. This may be due to the MEMO oligomers surrounding the particles. However, as the

Conclusion

The microstructure for the transparent SiO2/UV-curable resin coatings with various MEMO concentrations depended on the adsorbed MEMO silane configuration and the amount of un-adsorbed MEMO oligomer. At low MEMO concentrations the phase separation between SiO2 nano-particles and HDDA monomer occurred and SiO2 nano-particles tended to migrate to the coating surface due to the incomplete surface coverage and the adsorbed MEMO molecules tending to orient parallel to the SiO2 surface. This may

Acknowledgment

The authors would like to express their thanks to the Ministry of Economic Affairs of the Republic of China for financially supporting this project (97-EC-17-A-08-S1-023).

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