Hybrids of colloidal silica and waterborne polyurethane

Waterborne polyurethane (WPU) was synthesized and followed by adding colloidal silica to prepare WPU–silica hybrids. The silica content in the hybrid thin films was varied from 0 to 50 wt%. The experimental results revealed that the viscosity of these hybrid solutions increased with increasing silica content and resulted in the aggregation of silica particle in the hybrid films. The latter result was evidenced by SEM examination. The effect of interaction between silica particle and urethane polymer chains is more significant with increasing silica content. The prepared hybrid films show much better thermal stability and mechanical properties than pure WPU. The optical transparence did not linearly decrease with increasing the silica fraction in the hybrid thin film. At below 20% silica content, the film transparence decreased with increasing silica content; the converse is true at above 20% silica content. These results showed that the prepared hybrid films demonstrated tunable transparence with the silica fraction in the films.

Transmittance variation of the hybrid films (ca. 0.5 mm thickness) with different silica content over a wavelength range of 200–1100 nm. As shown in the inset, the transmittance at 633 nm decreases from 92% of pure WPU to 20% of the hybrid with 20% silica content, and then gradually increases from 20 to 87% of the hybrid with 50% silica content.Figure optionsDownload as PowerPoint slide