Mixed Matrix Membranes Based on Torlon® and ZIF-8 for High-Temperature, Size-Selective Gas Separations

Torlon® is a thermally and plasticization-resistant polyamide imide characterized by low gas permeability at room temperature. In this work, we aimed at improving the polymer performance in the thermally-enhanced He/CO2 and H2/CO2 separations, by compounding Torlon® with a highly permeable filler, ZIF-8, to fabricate Mixed Matrix Membranes (MMMs). The effect of filler loading, gas size, and temperature on the MMMs permeability, diffusivity, and selectivity was investigated. The He permeability increased by a factor of 3, while the He/CO2 selectivity decreased by a factor of 2, when adding 25 wt % of ZIF-8 at 65 °C to Torlon®; similar trends were observed for the case of H2. The MMMs permeability and size-selectivity were both enhanced by temperature. The behavior of MMMs is intermediate between the pure polymer and pure filler ones, and can be described with models for composites, indicating that such materials have a good polymer/filler adhesion and their performance could be tailored by acting on the formulation. The behavior observed is in line with previous investigations on MMMs based on glassy polymers and ZIF-8, in similar conditions, and indicates that ZIF-8 can be used as a polymer additive when the permeability is a controlling aspect, with a proper choice of loading and operative temperature.

Determining the Self-Limiting Electrospray Deposition Compositional Limits for Mechanically Tunable Polymer Composites

Electrospray deposition (ESD) is a versatile micro/nano coating technology that utilizes the competition between surface charge of a droplet and its surface tension to create monodisperse generations of micro/nano droplets. ESD can deposit uniform thin films by including dilute solutes in these droplets. One mode of ESD, self-limiting electrospray deposition (SLED), has been shown to exist when glassy polymers are sprayed in a volatile solvent below the polymer glass transition temperature (Tg). This leads to charge accumulation on the coating surface that slows the growth of the film thickness. Since solutes can be easily blended in dilute ESD solutions, we investigate the SLED limits of self-limiting and non-self-limiting solute blends. As a motivating application, we focus on mechanical properties of the film. Specifically, we blend self-limiting polystyrene (PS) and SU-8 epoxy resin with different non-self-limiting mechanical modifiers, such as plasticizers and curing agents. To characterize the resulting morphologies and mechanical properties, we employ scanning electron microscopy and nanoindentation of as received and smoothed films. The results illustrate the formation of composited polymers that exhibit self-limiting ability by SLED, depending on the interaction between the two components. Further, mechanical properties could be effectively fine-tuned within these compositional ranges. This signifies the 3D coating capabilities through SLED can be implemented incorporating additional functionalities and properties beyond the base matrix.