Search for: All records

EVOH’s excellent gas barrier properties have enabled its continued market growth in numerous applications including food packaging, fuel tanks, and construction. However, EVOH’s susceptibility to thermo-oxidation limits its ability to be reprocessed. While it is generally known that EVOH degradation leads to cross-linking, detailed degradation rates and mechanisms are not well established. Understanding EVOH degradation has been elusive because readily accessible thermal and spectroscopy methods do not reveal significant changes. Moreover, gel permeation chromatography requires specialized solvents and columns. We report that measuring changes in viscoelasticity with time-resolved rheology (TRR) is a facile way to monitor the temporal dynamics of EVOH degradation. TRR was performed on EVOH grades with ethylene copolymer contents of 27, 32, 48 mol%. As expected, the grade with the highest ethylene content was the most stable. However, with time, all the EVOH grades transitioned from a Carreau-like fluid to a power law fluid and no longer exhibited terminal behavior. Cole-Cole plots also revealed that EVOH relaxation evolved from rapid process into a long, complex process consistent with network formation. The mechanism of degradation was further elucidated by using 13C distortionless enhancement of polarization transfer (DEPT-135) nuclear magnetic resonance spectroscopy. These results showed that degradation occurred by ring-opening of lactone terminal groups that led to cross-linking. This enhanced understanding provides a foundation for developing methods to probe and mitigate EVOH degradation. 

Mineral precipitation reactions in porous media can change the porosity and permeability of the rock formations. Predicting the rate of reaction and impacts on formation properties is challenging due to a lack of understanding of mineral precipitation reaction kinetics and mechanisms in porous media. This is furthermore challenging due to the highly heterogeneous nature of natural porous media. Here, we aim to develop a novel experimental platform leveraging 3D printing to facilitate replicable mineral precipitation experiments in controlled, heterogenous porous media systems. This requires fundamental understanding of the kinetics of mineral precipitation on the polymer materials used to fabricate the 3D printed porous media. In this work, we manipulate (via sulfonation) material surfaces (high impact polystyrene, HIPS) to promote calcite precipitation from supersaturated solutions to inform the design of synthetic subsurface systems. Calcite precipitation on HIPS films of varied surface sulfonation is confirmed using X-ray diffraction (XRD) analysis and weight-based precipitation experiments where increased precipitation with increased surface functionalization and solution saturation index are observed. This approach is then applied to 3D-printed porous media to enhance understanding of geochemical reactions, specifically calcite precipitation. Three dimensional images of Bentheimer Sandstone are used as the basis for 3D-printed porous media samples. Two 3D-printed samples were functionalized with acid to activate the surface and promote mineral precipitation. Functionalized and unfunctionalized samples underwent calcite precipitation core flooding experiments with oversaturated calcite solutions for 96 hours. Three dimensional X-ray micro-CT imaging revealed calcite growth in functionalized samples, with a calcite volume fraction of approximately 2.6% and a substantial reduction in porosity. Unfunctionalized samples exhibited diminished calcite precipitation and porosity changes. These findings demonstrate that reactive 3D-printed porous media can provide a versatile geochemical modeling and experimentation platform. Functionalizing 3D printed samples enhances reactivity, allowing investigations of mineral precipitation processes in complex porous media. This research highlights the potential for further exploration of 3D-printed media in various geochemical contexts. 

Carboxylate anions of various chain lengths are important molecules for many applications such as CO2 reduction, membrane-based bioreactors, etc. Also, carboxylate anions are ubiquitous in biological molecules such as amino acids, fatty acids, etc. Therefore, understanding the transport behavior of carboxylates of different chain lengths in polymer materials is important both as a fundamental phenomenon but also for designing materials for applications. Here, we characterized transport behavior by measuring the permeability (P), and total partition coefficient (K) for a series of polymer membranes for four model carboxylate salts—sodium salts of formate (NaOFm), acetate (NaOAc), propionate (NaOPr), and butanoate (NaOBu)—at varied upstream salt concentrations (0.1–1 M) or a series of polyethylene glycol diacrylate (PEGDA)-based membranes with 1) varying pre-polymerization water content; 2) varying uncharged side chain comonomer (polyethylene glycol methacrylate, PEGMA), and 3) varying charged comonomer)2-acrylamido-2-methyl-1-propanesulfonic acid, AMPS). Also, diffusivity values of the four salts through the membranes have been calculated based on the solution diffusion model equation (Pdouble bondK × D), experimentally obtained permeability, and total partition coefficients. For a majority of these membranes, NaOFm's permeability is much higher than the other three carboxylate salts (NaOAc, NaOPr, and NaOBu) seemingly due to the lower chain length and thereby smaller hydrated diameter. In terms of total partition coefficient, a size-based trend is not observed. For example, NaOBu's total partition coefficient (K) is generally the largest among the four, and at higher upstream salt concentrations (1 M), the values of the total partition coefficients of the four salts converge. From this we conclude that the carboxylate salt transport through these PEGDA-based non-porous dense membranes to be primarily driven by kinetics and not sorption. 

Understanding multi-component transport through polymer membranes is critical for separation applications such as water purification, energy devices, etc. Specifically for CO2 reduction cells, where the CO2 reduction products (alcohols and carboxylate salts), crossover of these species is undesirable and improving the design of ion exchange membranes to prevent this behavior is needed. Previously, it was observed that acetate transport increased in copermeation with alcohols for cation exchange membranes consisting of poly(ethylene glycol) diacrylate (PEGDA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and that the inclusion of poly(ethylene glycol) methacrylate (PEGMA) (n = 5, n represents the number of ethylene oxide repeat units) could suppress this behavior. Here, we further investigate the role of PEGMA in modulating fractional free volume and transport behavior of alcohols and carboxylates. PEGDA-PEGMA membranes of varied membranes are fabricated with both varied pre −polymerization water content at constant PEGMA (n = 9) content and varied PEGMA content at two pre −polymerization water contents (20 and 60 wt.% water). Permeability to sodium acetate also decreases in these charge-neutral PEGDA-PEGMA membranes compared to PEGMA-free films. Therefore, incorporation of comonomers such as PEGMA with long side chains may provide a useful membrane chemistry structural motif for preventing undesirable carboxylate crossover in polymer membranes. 

In many applications of hydrated, dense polymer membranes—including fuel cells, desalination, molecular separations, electrolyzers, and solar fuels devices—the membrane is challenged with aqueous streams that contain multiple solutes. The presence of multiple solutes presents a complex process because each solute can have different interactions with the polymer membrane and with other solutes, which collectively determine the transport behavior and separation performance that is observed. It is critical to understand the theoretical framework behind and experimental considerations for understanding how the presence of multiple solutes impacts diffusion, and thereby, the design of membranes. Here, we review models for multicomponent diffusion in the context of the solution-diffusion framework and the associated experiments for characterizing multicomponent transport using diffusion cells. Notably, multicomponent effects are typically not considered when discussing or investigating transport in dense, hydrated polymer membranes, however recent research has shown that these effects can be large and important for understanding the transport behavior. 

Polymer composites are becoming an important class of materials for a diversified range of industrial applications due to their unique characteristics and natural and synthetic reinforcements. Traditional methods of polymer composite fabrication require machining, manual labor, and increased costs. Therefore, 3D printing technologies have come to the forefront of scientific, industrial, and public attention for customized manufacturing of composite parts having a high degree of control over design, processing parameters, and time. However, poor interfacial adhesion between 3D printed layers can lead to material failure, and therefore, researchers are trying to improve material functionality and extend material lifetime with the addition of reinforcements and self-healing capability. This review provides insights on different materials used for 3D printing of polymer composites to enhance mechanical properties and improve service life of polymer materials. Moreover, 3D printing of flexible energy-storage devices (FESD), including batteries, supercapacitors, and soft robotics using soft materials (polymers), is discussed as well as the application of 3D printing as a platform for bioengineering and earth science applications by using a variety of polymer materials, all of which have great potential for improving future conditions for humanity and planet Earth.