Katsumi Motegi

Heat Resistant Transparent Flexible Film Obtained from Two Tetraphenylphosphonium Modified Smectites with Different Particle Size

Transparent clay films were prepared using tetraphenyl phosphonium (TPP) modified smectites (TPP-SA, TPP-HE, and TPP-SA-HE), which were prepared by ion exchange of either synthetic saponite (SA) or synthetic hectorite (HE) as well as a mixture of these two kinds of smectites (SA-HE) with TPP-bromide (TPP-Br). Uniform liquid dispersions of these TPP-smectites were successfully prepared by adding N,N-dimethylformamide (DMF) to hydrous gels of TPP-smectites. Finally, transparent self-supported films of about 30 µm thickness were prepared by casting these dispersions. From the optical studies, it was confirmed that the transparent clay films maintained their optical transparency in the visible range even after annealing at 350 °C for an hour. Particularly, haze value of the TPP-SA-HE film decreased by one-third compared to TPP-SA, and it was also confirmed that the flexibility of TPP-SA-HE film was better than that of TPP-HE. From the cross-sectional scanning electron microscope (SEM) images, it was confirmed that TPP-SA film has large voids, which causes scattering of light compared to TPP-HE. Finally, the average void size was reduced by mixing these two TPP-smectites with different particle size.