Interfacial and dielectric behavior of polymer nano-composites: Effects of chain stiffness and cohesive energy density

Bimodal Polymer End-Linked Nanoparticle Network Design Strategy to Manipulate the Structure-Mechanics Relation

A kind of bimodal polymer end-linked network employing nanoparticles (NPs) as net points has been designed and constructed through coarse-grained molecular dynamics simulation. We systematically explore the effects of the molecular weight (length of the long polymer chains), chain flexibility, and temperature on the accurate distribution of the spherical NPs and the resulting mechanical properties of the bimodal network. It is found that the NPs can be dispersed well, and a larger average distance between the NPs is realized with the increase of the length of the long polymer chains, the rigidity of short and long chains, and the temperature. There is a linear relationship between the average interparticle distance of NPs and the arithmetical average of the root-mean-square end-to-end distance of long and short chains. By adopting the uniaxial deformation, the stress-strain behavior and the bond orientation are examined. The results illustrate that introducing the short chains into the uniform long chains network can notably improve the tensile stress-strain performance. The bond orientation behaviors present that short chains are more prone to be oriented and stretched, contributing to more stress during the stretching process. Furthermore, enhanced stress-strain behaviors can be observed by manipulating the chain stiffness and temperature. Interestingly, the bimodal end-linked network reveals a distinctively enhanced stress-strain behavior versus the temperature, which is opposite to that of traditional physically mixed polymer nanocomposites (PNCs), attributed to a higher entropic elasticity and the uniform dispersion of NPs of the end-linked system at high temperatures. The network exhibits a linear relationship for the stress at a fixed strain versus the temperature. Notably, it is indicated that the contribution of entropy accounts for most of the total stress, while the change of internal energy only accounts for a small part, which is consistent with the experimental observation of the classic rubber elastic theory. In general, our study demonstrates a rational route to precisely control the spatial dispersion of the NPs and effectively tailor the mechanical properties of PNCs.

Enhanced mechanical, thermal, and UV-shielding properties of poly(vinyl alcohol)/metal–organic framework nanocomposites

Metal–organic framework (HKUST-1) nanoparticles were successfully synthesized, and poly(vinyl alcohol) (PVA)/HKUST-1 nanocomposite films were fabricated by a simple solution casting method. Our results showed that the addition of HKUST-1 caused a remarkable enhancement in both thermal stability and mechanical properties of the PVA nanocomposites, due to the homogeneous distribution of HKUST-1 and the strong interfacial interactions between PVA and HKUST-1. With incorporation of 2 wt% HKUST-1, the degradation temperature of the nanocomposites was about 33 °C higher than that of pure PVA. At the same time, the Young's modulus and tensile strength of the nanocomposites was approximately 137% and 32% higher than those of pure PVA, respectively. Moreover, the PVA/HKUST-1 nanocomposites also showed strikingly enhanced UV-shielding ability as well as satisfactory visible light transmittance, which revealed that HKUST-1 nanoparticles could act as a good UV absorber in nanocomposites. This work provides a novel and simple method for producing UV-shielding materials with simultaneously enhanced thermal and mechanical properties, which have potential applications in UV protection areas.

PVA/HKUST-1 nanocomposites prepared by a simple solution casting method displayed significantly enhanced thermal stability, mechanical and UV-shielding properties.