Designing the nano-scale interface in polymer nanocomposites as a driving parameter of the macroscopic properties for new functional materials – NANOINTERPROP

Over the last two decades it has become well-accepted that incorporating nanoparticles (NPs) into a polymer matrix can lead to materials with significantly improved properties, e.g., mechanical, optical, electrical or gas barrier. As a result, polymers filled with NPs - polymer nanocomposites (PNCs) – have the potential to strategically impact many critical emerging industrial applications like energy storage, tires, paint and medical implants. These interesting mixtures, whose structure and dynamics are driven by nanoscale interactions, have also opened up a series of fundamental physics questions related to the role of polymer chain confinement, entropic elasticity and colloidal aggregation in this context. Up to now, the field of PNCs research has mainly focused on the optimization of the filler contribution – specifically, the controlling the NP spatial arrangement in the polymer matrix – to improve the macroscopic material properties. However, it’s not obvious how to extract general trends about the mechanisms governing the structure-property relationships. One has some evidence showing clear correlation between the filler morphology and the macroscopic properties, for example the concept of NP percolation seems to underpin mechanical reinforcement, electrical and thermal conductivity in these hybrid materials. However, it is unclear if this percolation effect results purely from the NPs or from the corresponding polymer-NP interfacial contribution involving the modification of polymer chain dynamics that can range from local monomer relaxations to the large-scale entanglement network diffusion. Significant breakthroughs can therefore be expected in the field of PNCs by overcoming the lack of the proper characterization of interfacial and chain dynamics. The proposal aims to develop new methodologies to design well-defined PNCs with modulated interfacial properties to optimize their application-relevant functionality. To reach this objective, we propose a self-consistent multi-disciplinary project incorporating polymer synthesis, PNC formulation and characterization (including dynamics and macroscopic properties) and transfer this knowledge to real-life, industrially critical tire systems (Michelin). It is critical to emphasize the novel aspects of the proposed work, especially in relation to the established state-of-the-art in this well-travelled field. First, we will synthesize a series of grafted spherical NPs presenting various degrees of chain-NP interactions, chain mobility, interfacial stiffness and polydispersity. While many previous works have also focused on such interfacial modification of the NP surface, we propose to introduce labile bonds so that we can systematically (and controllably) “degraft” chains from the NPs and examine the deterioration of properties with the “worsening” interface, while presumably not affecting NP percolation. Secondly, we will design a new class of PNCs by controlling the NP dispersion state focusing of a new assembly paradigm. While many previous works have used two strategies, namely NP surfactancy or flow-induced effects to achieve this goal, here we propose to control NP assembly by a new mechanism, i.e., the rate of crystallization of a semi-crystalline polymer host. Finally, we shall transfer methodologies and concepts to systems relevant to the industrial manufacture of tire. Hence the project presented is a research collaborative project PRCE between four partners including an industrial partner, experts in (i) innovative grafting polymerization, (ii) theoretical and experimental studies to assemble these functionalized NPs in a polymer matrix and (iii) characterizing and modeling the macroscopic functionalities of the composite materials in line with structure and dynamics. We believe this collaboration, which builds on a long-standing relationship between the different partners, is central to achieving the goal of disruptively impacting industrial practice in this field.