Development of flexible organo-saponite films and their transparency at high temperature

We developed novel transparent saponite films with excellent thermal stability and water resistance. The transparent saponite films were composed of either 1-ethyl-3-methyl imidazolium saponite (EMI-SA) or tetraphenyl phosphonium saponite (TPP-SA), which were produced by ion exchange reaction of synthetic saponite (SA) with 1-ethyl-3-methyl imidazolium bromide (EMI-Br) or tetraphenyl phosphonium bromide (TPP-Br). We dispersed these organo-saponites, with poor swelling properties and dispersibility, in N, N-dimethylformamide (DMF). We produced a transparent self-supported film by casting. Coloring of the films at high temperature indicated its excellent thermal stability up to 300 °C. Especially, TPP-SA self-supported film showed excellent thermal stability and good flexibility, showing little coloring up to 400 °C with a decomposition temperature > 500 °C. It showed transparency of > 80% in the visible-light region, with high flexibility, and good water resistance. These results demonstrate that TPP-SA self-supported films are a promising transparent material for various applications.