Polyethylene three-dimensional nano-networks: How lateral chains affect metamaterial formation

Polymers occupy a central role in current society due to their utility and versatile properties. As part of the class of soft materials, polymers have also been employed in research through nanostructuration and functionalization, looking for the development of new metamaterials with wide applicability in science and society. A particular polymer, Polyethylene, has been widely used both in research and commodities, and new ways to nanostructure and improve its functionality should be considered. Here, we report on the nanostructuration of polyethylene for the fabrication of three-dimensional nanonetworks, by resorting to 3 different variants of polyethylene: low density, high density, and ultra-high molecular weight. Through the melt infiltration of these polymers into well-known three-dimensional interconnected anodic aluminum oxide templates (3D-AAO), a study can be performed to understand the effects of the chain length, structure, and chain-branching of the used polymers on the stability and integrity of the resulting polymeric nanonetworks. This was accomplished by performing infiltrations in the presence of excess bulk material and quenching the infiltration process to access transient infiltration stages. The morphology of these networks was analyzed through SEM and STEM-HAADF to understand the differences arising from polymer structure. The observed results are interpreted through the use of the Lucas-Washburn equation for capillary flow and the determination of the critical contact angle for spontaneous capillary infiltration. The resulting metamaterials also exhibit photonic responses, resulting from the replication of the periodic nature of the employed templates.