Abstract
The current work presents a new approach to achieve high quality dispersion of surfactant-free nanoclay tactoid particles in sub-micron thin films despite the absence of organic modifier. Natural Montmorillonite particles, Na+ Cloisite, were dispersed in thin films of polycaprolactone (PCL) through a flow coating technique assisted by ultra-sonication. Wide-angle X-ray scattering (WAXS), grazing-incidence wide-angle X-ray scattering (GI-WAXS), and transmission electron microscopy (TEM) were used to confirm the level of natural clay dispersion down to the level of tactoids (sub-micron scale stacks of clay sheets). These characterization techniques were carried out in conjunction with an analysis of nanomechanical properties via strain-induced buckling instability for modulus measurements (SIEBIMM), a high-throughput technique to characterize thin film mechanical properties. The buckling patterns indicate that the natural clay tactoids separate buckling-enhancing (high-modulus) crystalline regions and interconnect buckling-suppressing amorphous (low-modulus) regions. Due to the tactoid length scale, the glass transition behavior of the composites as characterized by broadband dielectric relaxation spectroscopy was unmodified by the clay. Likewise, the glass transition temperature, T-g, and fragility (slope of relaxation time behavior approaching T-g), remain unaffected, indicating that these dispersed tactoids do not induce pronounced confinement effects on dynamics. POLYM. ENG. SCI., 58:1285-1295, 2018. (c) 2018 Society of Plastics Engineers