Epoxy siloxane/ZnO quantum dot nanocomposites: Model-fitting and model-free approaches to kinetic analysis of non-isothermal curing process

In this paper, we report on synthesis of ZnO quantum dots (QDs) nanoparticles with an epoxy siloxane composition as surface modifier, which facilitated the preparation of uniform epoxy siloxane based nanocomposite thanks to the compatibility of epoxy siloxane resin with surface modified ZnO QDs. The objective of this study was to evaluate the influence of zinc oxide quantum dots (ZnO QDs) on the reaction between poly (dimethyl siloxane), diglycidyl ether terminated (Epoxy-Siloxane), and 1,3-bis (amino methyl) cyclohexane (1,3BAC). Epoxy-Siloxane was filled with ZnO QDs at four treatment levels (0, 0.05, 0.1, and 0.15 wt.%) via direct dispersion method. After preparing the filled and unfilled samples, they were mixed with 1,3BAC after which their thermal behavior was studied using differential scanning calorimetry (DSC) under non-isothermal conditions. The reaction kinetics were derived using model-fitting methods as well as two different isoconversional approaches, i.e. the Friedman method and Ozawa-Flynn-Wall method. In the fitting procedure, the nth order coupled with autocatalysis model yielded relatively good results. The results indicated that the ZnO QDs incorporated into Epoxy-Siloxane slightly raised the activation energy of the reaction between epoxy siloxane and 1,3BAC, except for the sample containing 0.1 wt.% ZnO QDs. It also revealed a significant increase in the activation energy from (similar to)50 to (similar to)100 kJ/mol, which may be considered as the percolation threshold of the system. Atomic force microscopy and water contact angle measurements presented significant changes in the surface properties of the Epoxy-Siloxane films with respect to the content of ZnO quantum dots.