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1. Selectivity and polarization in water channel membranes: lessons learned from polymeric membranes and CNTs

   https://doi.org/10.1039/C8FD00054A  

   Freger, Viatcheslav ( January 2018 , Faraday Discussions)

   Water channels are employed by nature to move pure water across cell membranes while selectively rejecting salts. At present, synthetic channels successfully mimic water permeation, yet even the best channels, such as carbon nanotubes (CNTs) and graphene oxide stacks, still fall short of the selectivity target. The present paper analyzes factors that may help to enhance and control salt rejection based on the lessons learned from conventional membranes and CNTs. First, it highlights the importance of raising the ion self-energy (dielectric mechanism), which suggests that having the channels both narrow and surrounded by a low-dielectric environment is key to highmore »selectivity. In contrast, pore charge alone is insufficient, yet it may help to enhance and tune ion rejection, provided that non-mean-field effects enhanced in low-dielectric pores, such as ion association and sorption, especially of H + and OH − ions, are properly understood and addressed in the channel design. Second, the role of concentration polarization (CP) is analyzed, which shows that the CP level is apparently low in isolated channels or microscopically small membranes. However, the geometry of the diffusion field should change and CP should increase drastically in macroscopic membranes incorporating densely spaced channel arrays. If not properly addressed in membrane design, the increased CP level in scaled-up channel-based membranes may significantly compromise the observed selectivity and require that target of selectivity be re-set to an even more challenging value. These points may help guide the future development of high-performance artificial water channels and their scale-up towards utilization in next-generation water purification membranes.« less
2. THE ACCOMMODATION COEFFICIENT OF SALINE SESSILE WATER DROPLETS EVAPORATING WITH VARYING NON-VOLATILE IMPURITY LOADS

   Murray, B ; Narayanan, S. ( July 2021 , 15th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics)

   Meyer, J. P. (Ed.)

   Air-water evaporation systems are ubiquitous in industrial applications, including processes such as fuel combustion, inkjet printing, spray cooling, and desalination. In these evaporation-driven systems, a fundamental understanding of mass accommodation at the liquid-vapour interface is critical to predicting and optimizing performance. Interfacial mass accommodation depends on many factors, such as temperature, vapour concentration, non-volatile impurity content, and non-condensable gasses present. Elucidating how these factors interact is essential to designing devices to meet demanding applications. Hence, high precision measurements are needed to quantify accommodation at the liquid-vapour interface accurately. Our previous study has shown surface averaged accommodation coefficients close to 0.001more »for pure water droplets throughout evaporation. While it is well established that saline non-volatile impurities reduce the evaporation rate of sessile droplets, the dynamic effect on mass accommodation during the droplet's lifespan is yet to be determined. In this work, we combine experimental and computational techniques to determine the accommodation coefficient over the lifespan of 10-3 to 1 molar potassium chloride-water droplets evaporating on a gold-coated surface into dry nitrogen. This study uses a quartz crystal microbalance as a high-precision contact area sensor. It also determines the non-volatile impurities in the droplet with a precision on the order of nanograms. The computational model couples macroscopic measurements with the microscopic kinetic theory of gasses to quantify hard-to-measure physical quantities. We believe this study will provide a basis for predicting evaporative device performance in conditions where non-volatile impurities are intrinsic to the application.« less
3. Electromechanical characterization of 3D printed dielectric material for dielectric electroactive polymer actuators

   Gonzalez, David ; Garcia, Jose ; Newell, Brittany ( January 2019 , Sensors and actuators. A, Physical)

   Dielectric electroactive polymers (DEAPs) represent a subclass of smart materials that are capable of converting between electrical and mechanical energy. These materials can be used as energy harvesters, sensors, and actuators. However, current production and testing of these devices is limited and requires multiple step processes for fabrication. This paper presents an alternate production method via 3D printing using Thermoplastic Polyurethane (TPU) as a dielectric elastomer. This study provides electromechanical characterization of flexible dielectric films produced by additive manufacturing and demonstrates their use as DEAP actuators. The dielectric material characterization of TPU includes: measurement of the dielectric constant, percentage radialmore »elongation, tensile properties, pre-strain effects on actuation, surface topography, and measured actuation under high voltage. The results demonstrated a high dielectric constant and ideal elongation performance for this material, making the material suitable for use as a DEAP actuator. In addition, it was experimentally determined that the tensile properties of the material depend on the printing angle and thickness of the samples thereby making these properties controllable using 3D printing. Using surface topography, it was possible to analyze how the printing path, affects the roughness of the films and consequently affects the voltage breakdown of the structure and creates preferential deformation directions. Actuators produced with concentric circle paths produced an area expansion of 4.73% uniformly in all directions. Actuators produced with line paths produced an area expansion of 5.71% in the direction where the printed lines are parallel to the deformation direction, and 4.91% in the direction where the printed lines are perpendicular to the deformation direction.« less
4. Carbon nanotube enhanced dynamic polymeric materials through macromolecular engineering

   https://doi.org/10.1039/D0MA00143K  

   Stopler, Erika B. ; Dodo, Obed J. ; Hull, Alexander C. ; Weaver, Kyle A. ; Chakma, Progyateg ; Edelmann, Richard ; Ranly, Logan ; Zanjani, Mehdi B. ; Ye, Zhijiang ; Konkolewicz, Dominik ( August 2020 , Materials Advances)

   Dynamic covalent Diels–Alder chemistry was combined with multiwalled carbon nanotube (CNT) reinforcement to develop strong, tough and conductive dynamic materials. Unlike other approaches to functionalizing CNTs, this approach uses Diels–Alder bonds between diene pendant groups on the polymer and the CNT surface πσ bonds acting as dienophiles. Experimental and simulation data align with the CNT reinforcement coming from dynamic covalent bonds between the matrix and the CNT surface. The addition of just 0.9 wt% CNTs can lead to an almost 3-fold increase in strength and 6–7 order of magnitude increases in electrical conductivity, and materials with 0.45 wt% CNTs showmore »excellent strength, self-healing and conductivity.« less
5. 3D Printed Stress Sensors for Non-Destructive Evaluation of Space Structures

   Perla Latorre-Suraez, Rohan Madathil ( April 2021 , AIAA 2021 Regional Student Conference, April 2021.)

   Self-sufficient and non-contact sensors play multiple roles in lunar, planetary exploration, and Earth structures. These sensors allow engineers to accurately examine structural integrity and defects on mechanical components for optimal operations. Structural integrity allows the industry to ensure the safety and capacity of key structures. Materials like α-alumina can be employed as sensors due to the photoluminescent properties that they possess. Piezospectroscopy is a non-destructive evaluation (NDE) method capable of capturing in-situ stress using α-alumina due to the chromium ion impurities that it contains. The chromium ion impurities carry spectral characteristics, that when excited with an Nd: YAG laser (532more »nm), demonstrate capabilities for structural integrity monitoring. In this work, a 3D printing method is developed to autonomously create sensors that are compatible with use in space environments. The 3D printing method intends to provide the industry flexible and adaptive solutions for structural integrity monitoring. This method includes a modified Fused Deposition Method printer by exchanging its original nozzle with a syringe base nozzle. The printing parameters such as printing speed, printing bed temperature, coating thickness, and syringe volume are determined during the testing process. Challenges include achieving uniform integration and nanoparticle dispersion as well as adhesion between the matrix and the substrates. The parameters to encounter these challenges will depend on the materials used. Experiments with three different volume fractions (VF) of α-alumina within an epoxy were performed to address the printing challenges. The sensors were applied to nine specimens, three of each VF but with varying deposition rates after the mixture process. These experiments considered the mixing and deposition method while testing the dispersion within the α-alumina and the epoxy matrix. The substrates, on which the epoxy matrix was deposited, underwent a surface treatment to ensure adhesion between the substrate and the sensor matrix. During this experiment, the epoxy matrix was deposited with a syringe onto a substrate and cured at room temperature. The specimens were tested with a tensile load using an electromechanical MTS. While the samples are tensile loaded, the sensors were characterized via photoluminescent piezo spectroscopy to determine which VF demonstrates the best stress sensing capabilities, along with the adhesion between the matrix and the substrate. The data collected allows the optimal VF to be established for future applications.« less