Structure and Rheological Properties of Polymer Nanocomposites with Bimodal Nanoparticle Sizes

Polymer nanocomposites (PNCs) have been used in many polymer-based applications based on their ability to improve the physical properties of clean polymers. To control the physical properties of PNC, many PNC studies have first changed the size of monodispersed nanofillers; however, polydispersed PNC systems have not been much discussed despite the frequent use of polydispersed nanofillers in the practical PNC application.

In this study, we introduce bimodal-sized nanofillers to PNC to examine how particle size distribution affects PNC structure and physical properties. The bimodal particle system exhibits unique dynamics and structures, and its properties can vary depending on the particle size ratio, the volume ratio between large/small particles, and the particle volume fraction. More importantly, the structure and rheological characteristics of PNC will also be systematically changed as the varying particle sizes create different interfacial layers of polymers. We composed the PNC model system with poly(ethylene glycol)/silica nanoparticles with varying size and volume fraction ratios of small/big particles, and the matrix polymer molecular weight. We found that PNCs with a high-volume fraction ratio of small particles can show enhanced modulus which can be sensitively dependent on the molecular weight of the polymer and its adsorption behavior.