Highly transparent flexible clay films modified with organic polymer: structural characterization and intercalation properties

Abstract

We are developing transparent flexible clay films with high thermal resistance and gas barrier properties. The clay films were fabricated by casting aqueous dispersions of synthetic Na⁺-saponite mixed with various loadings of water-soluble organic polymer. In this paper, the structural, optical, and physical properties of the films are reported. The structure of these films has been found to have an alignment of densely packed clay platelets interspersed with polymer chains between clay platelet edges. The parallel stacking of clay platelets is enhanced by adsorption of anionic polymer on the positively charged edges of the clay platelets so that excellent optical transparency is maintained even for high clay loading (up to 90 wt%). Also, polymer chains bounded on particle edges are tightly confined by upper and lower layers of clay platelets, rendering these films more thermally stable. The degradation temperature of the films is more than 350 °C. Differential scanning calorimetry analysis reveals that the melting point of the polymer in the clay layers is shifted towards the higher temperature range, up to 440 °C. However, the segregation of polymers towards the film surface occurs with the polymer loading, which reduces the thermal resistance of the film due to weaker interaction of adsorbed polymer on the film's surface. Consequently, films with higher clay loading (>80 wt%) provide excellent optical and physical properties, these films will be promising for a wide variety of applications such as displays or other electronic devices.