ERI: Controlling the Hierarchical Porosity and Surface-Functionalized Nanostructure of Polyethylene using Amphiphilic Additives

Porous polymeric membranes are used for a variety of applications including gas and ion separations, but there is a significant need for alternative strategies to design polymers with tunable porosity using scalable processes, to overcome limitations presented by the trade-off between permeability and selectivity. In a recently discovered processing method, commercial microporous high-density polyethylene (HDPE) pellets can be swollen with fatty acids or other amphiphiles to form a surface-functionalized, nanoporous structure. This Engineering Research Initiative (ERI) project will utilize comprehensive structural characterization to study HDPE processed with this method to establish design rules that lead to control of the membrane characteristics. The knowledge established in this research will aid in the development of a new scalable process for developing nanoporous membranes, which will serve to address the societal challenge of tuning permeability and selectivity in porous membranes. This project will involve the mentorship and training of one graduate and two undergraduate students, and outreach to local high school students, who will learn about materials research and advanced manufacturing. This project will identify how the process of swelling polyethylene (PE) with different amphiphiles can lead to control of the porosity and hierarchical nanostructure. This research has the potential to address a significant knowledge and technical gap in the creation of polyethylene-based membranes with controlled nanostructure, porosity, and surface functionalization, and a new fundamental understanding of how to attain this. This work will study in detail how amphiphile characteristics impact their co-crystallization with the HDPE during this new swelling process, and how this crystallization in turn affects the hierarchical nano- and microporosity of the resulting material. A wide range of amphiphiles will be used with varying head groups and PE-type tail with lengths. Complementary techniques will be used to study the hierarchical structure: differential scanning calorimetry to study crystallinity ( 2 μm in size; broadband dielectric spectroscopy to study total porosity and corresponding changes with additional high temperature annealing. The primary outcome of this work will be the establishment of a set of design rules for predicting crystallinity and hierarchical porosity based on amphiphile head group and tail length in HDPE processed with this new method, potentially transforming the landscape of porous membranes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.