Epoxy-siloxane molecular hybrid materials for application of flexible hard coatings

Abstract

A glass has played a key role providing good transparency and reliable protection of a screen for most flat-panel displays. However, the transition toward the era of flexible electronics make the glass an impractical option as a cover window due to its intrinsic stiffness and brittleness. Recently, hardware innovation for commercialization of foldable displays have focused on the development of new optically transparent protective materials as a substitute of the glass, simultaneously attaining high strength and elastic compliance known to be mutually exclusive. In this dissertation, research for the design of innovative transparent hybrid material, exhibiting glass-like wear resistance, plastic-like compliance and large elastic recoverability resulted from the strategy to increase the chemical bonds of intra- and inter-phases at the molecular level, is conducted as follows. First, the synthetic mechanism of epoxy siloxane molecular hybrid (ESMH) are developed using a simple, mass-producible and low-energy-consuming method based on the synergetic combination of highly condensed siloxane backbones by the sol-gel reactions that are maximally cross-linked by a cationic ring-opening polymerization of cycloaliphatic epoxide groups. In addition, by introducing the moisture annealing process, the epoxy conversion increased and the volume expansion occurred which resulted in the relaxation of residual stresses due to the volume shrinkage by the epoxy linking. Second, the mechanical properties are characterized using nanoindentation experiments and in-situ compression and bending tests to visually and quantitatively validate the real mechanical responses under the same mode it will encounter during the actual applications, which shows that the ESMH pierces the limitation of mechanical properties for engineering materials. Lastly, on the basis of structure-property relationships in epoxy-siloxane hybridization, we propose that these brilliant properties to intimate chemical bonds of intra- and inter-phases at the molecular level. These findings create a new selection to be applied for flexible protective coatings in flexible cover windows.