Kwangwon Seo

Effect of tetrapod ZnO whiskers on the physical and moisture barrier properties of transparent polyimide/TZnO-W composite films

Tetrapod zinc oxide whiskers (TZnO-Ws) were successfully prepared by a thermal oxidation method and confirmed using scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD). A series of polyimide (PI)/TZnO-W composite films containing the as-prepared various TZnO-W contents were prepared and their physical properties were investigated to understand their potential use in flexible displays. The morphology, physical, and moisture barrier properties of the PI/TZnO-W composite films were interpreted as a function of the TZnO-W content. The PI/TZnO-W composite films exhibited an optical transparency greater than 80% at 550 nm (≤0.5 wt% TZnO-W content), a low coefficient of thermal expansion (CTE), and enhanced glass transition temperature. However, the thermal decomposition temperature decreased as the TZnO-W content increased. Although the mechanical strength increased up to 0.3 wt% TZnO-W content, it decreased due to poor interfacial interaction with high TZnO-W loading. The water vapor transmission rate (WVTR) and water uptake of the composite films, which were strongly dependent upon their morphological and chemical structure, varied from 508.3 to 325.2 g/m2/day and 3.7 to 1.3 wt%, respectively, greatly decreased as the TZnO-W content increased. The water resistance capacity of PI was greatly enhanced and moisture diffusion in the pure PI was retarded by incorporating the TZnO-W.

Residual stress behavior and physical properties of transparent polyimide/surface-modified CaCO3 nanocomposite films

A series of polyimide (PI) nanocomposite films with various surface-modified colloidal calcium carbonate (SCaCO3) contents were prepared and their physical properties were investigated to understand their possible use as polymer substrates. The morphology, thermal stability, residual stress behavior, moisture barrier and optical properties of nanocomposite films were investigated as a function of the SCaCO3 content and were found to be strongly dependent upon the chemical and morphological structures. With the addition of up to 0.5 wt% SCaCO3 in the PI matrix, resultant nanocomposite films exhibit not only enhanced thermal properties, but also minimized residual stress and excellent optical properties, simultaneously. With increasing SCaCO3 content, the water vapor transmission rate (WVTR) is greatly decreased from 630.76 to 484.22 g/m2/day. The residual stress was in the range of 26.0 to 12.1 MPa and is highly dependent on both temperature variation and SCaCO3 content. Although the residual stress becomes lower at 0.5 wt% SCaCO3 content, it increases at relatively high SCaCO3 loadings due to inadequate dispersion of the SCaCO3 and low interfacial interactions between the polymer and filler surfaces. Therefore, further studies are needed to maximize the performance of nanocomposite films by enhancing the compatibility of the polymer matrix and fillers.