Nano-effect is one of the common phenomena in nanofiller reinforced polymer nanocomposites. Over the past two decades, a general hypothesis proposed by most material scientists is that the nano-effect of nanofillers played a critical role in significant reinforcement of polymers. Due to the lack of proper experimental approaches and theoretical models, up to now, most trials for characterization of the nano-effect are rather qualitative. Moreover, these qualitative characterization approaches are unable to prove the existence of the nano-effect since incorporating nanofillers may also reduce the mechanical properties in some circumstances. In order to characterize the nano-effect precisely, a novel approach was invented in this study to quantitatively reveal the nano-effect of...[ Read more ]

Nano-effect is one of the common phenomena in nanofiller reinforced polymer nanocomposites. Over the past two decades, a general hypothesis proposed by most material scientists is that the nano-effect of nanofillers played a critical role in significant reinforcement of polymers. Due to the lack of proper experimental approaches and theoretical models, up to now, most trials for characterization of the nano-effect are rather qualitative. Moreover, these qualitative characterization approaches are unable to prove the existence of the nano-effect since incorporating nanofillers may also reduce the mechanical properties in some circumstances. In order to characterize the nano-effect precisely, a novel approach was invented in this study to quantitatively reveal the nano-effect of nanotube reinforced polymer nanocomposites. This approach included a series of specially designed experiments and a novel theoretical model. Both experiments and theoretical model are only controlled by the dimension of the reinforcing fiber at a certain loading and aspect ratio. Having only one variable in the experiments and theoretical model, other influencing factors which may affect the result can be fundamentally eliminated. Hence, this approach can substantially prove existence and origin of the nano-effect, and can characterize it in a quantitative way. In this study, halloysite nanotube (HNT), a typical natural nanotube, was selected as the nano-sized reinforcement due to its straight nano-structure and superior mechanical properties. And, polystyrene (PS) was chosen as the polymer matrix because of its amorphous nature and stable properties during processing. Using this approach, the nano-effect of HNTs in PS matrix was found by the experiments and numerically proven by a novel theoretical model. The huge interphase volume in the nanocomposites was characterized as the origin of the nano-effect. Furthermore, a functional relationship between Young’s modulus and radius of the reinforcing fibers at a fixed filler loading was established. Based on the results, the Young’s modulus value of the composites will be exponentially increased if the radius of the reinforcing fiber was below 200nm while it will be constant if the fiber’s radius is larger than 500nm. Hence, our theory clearly indicated that the nano-effect is only related to the dimension of the reinforcing fiber and will be triggered if its radius is under 200nm. This study enriches the fundamental knowledge of the nano-effect, which not only provides an innovative experimental approach but also presents a critical theoretical comprehension to quantitatively characterize and evaluate the nano-effect of nanofillers in polymer nanocomposites.