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  1. Ultraviolet (UV) printing of photopolymers is a widely adopted manufacturing method because of its high resolution and throughput. However, available printable photopolymers are typically thermosets, resulting in challenges in postprocessing and recycling of printed structures. Here, we present a new process called interfacial photopolymerization (IPP) which enables photopolymerization printing of linear chain polymers. In IPP, a polymer film is formed at the interface between two immiscible liquids, one containing a chain-growth monomer and the other containing a photoinitiator. We demonstrate the integration of IPP in a proof-of-concept projection system for printing of polyacrylonitrile (PAN) films and rudimentary multi-layer shapes . IPP shows in-plane and out-of-plane resolutions comparable to conventional photoprinting methods. Cohesive PAN films with number-average molecular weights greater than 15 kg mol–1 are obtained, and to our knowledge this is the first report of photopolymerization printing of PAN. A macrokinetics model of IPP is developed to elucidate the transport and reaction rates involved and evaluate how reaction parameters affect film thickness and print speed. Last, demonstration of IPP in a multilayer scheme suggests its suitabiliy for three-dimensional printing of linear-chain polymers. 
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    Free, publicly-accessible full text available June 28, 2024
  2. To help straddle the breadth of research on doctoral student stress, our team sought to explore the landscape of doctoral student stressors by interviewing an intentionally stratified sample of doctoral students four times during the course of an academic year. We present an overview of our research process and the top 10 most reported stressors from analysis of our interview data. Further, we report on the most frequent coping strategies used by students in our sample, contributing additional coping strategies used by engineering doctoral students. Understanding the most common factors which contribute to the stresses experienced by doctoral students and these students' effective coping strategies can support students, advisors, and departments to develop proactive interventions and strategies that support well-being and retention. 
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    Free, publicly-accessible full text available June 1, 2024
  3. Abstract

    Polyetherimides (PEI) are high‐performance thermoplastic polymers featuring a high dielectric constant and excellent thermal stability. In particular, PEI thin films are of increasing interest for use in solid‐state capacitors and membranes, yet the cost and thickness are limited by conventional synthesis and thermal drawing techniques. Here, a method of synthesizing ultrathin PEI films and coatings is introduced based on interfacial polymerization (IP) of poly(amic acid), followed by thermal imidization. Control of transport, reaction, and precipitation kinetics enables tailoring of PEI film morphology from a nanometer‐scale smooth film to a porous micrometer‐scale layer of polymer microparticles. At short reaction times (≈1 min) freestanding films are formed with ≈1 µm thickness, which to our knowledge surpass commercial state‐of‐the‐art films (3–5 µm minimum thickness) made by thermal drawing. PEI films synthesized via the IP route have thermal and optical properties on par with conventional PEI. The use of the final PEI is demonstrated in structurally colored films, dielectric layers in capacitors, and show that the IP route can form nanometer‐scale coatings on carbon nanotubes. The rapid film formation rate and fine property control are attractive for scale‐up, and established methods for roll‐to‐roll processing can be applied in future work.

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  4. Automated handling of microscale objects is essential for manufacturing of next-generation electronic systems. Yet, mechanical pick-and-place technologies cannot manipulate smaller objects whose surface forces dominate over gravity, and emerging microtransfer printing methods require multidirectional motion, heating, and/or chemical bonding to switch adhesion. We introduce soft nanocomposite electroadhesives (SNEs), comprising sparse forests of dielectric-coated carbon nanotubes (CNTs), which have electrostatically switchable dry adhesion. SNEs exhibit 40-fold lower nominal dry adhesion than typical solids, yet their adhesion is increased >100-fold by applying 30 V to the CNTs. We characterize the scaling of adhesion with surface morphology, dielectric thickness, and applied voltage and demonstrate digital transfer printing of films of Ag nanowires, polymer and metal microparticles, and unpackaged light-emitting diodes. 
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  5. Abstract

    Zwitterionic surfaces are increasingly explored as antifouling coatings due to their propensity to resist protein, bacterial, and cell adhesion and are typically applied as polymeric systems. Here, the self‐assembly of strongly interacting small molecule amphiphiles is reported to produce nanoribbons for antifouling applications. Synthesized amphiphiles spontaneously form micrometers‐long nanoribbons with nanometer‐scale cross‐sections and intrinsically display a dense coating of zwitterionic moieties on their surfaces. Substrates coated with nanoribbons demonstrate concentration‐dependent thicknesses and near superhydrophilicity. These surface coatings are then probed for antifouling properties and substantial reductions are demonstrated in protein adsorption, bacterial biofilm formation, and cell adhesion relative to uncoated controls. Harnessing cohesive small molecule self‐assembling nanomaterials for surface coatings offers a facile route to effective antifouling surfaces.

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  6. Abstract

    Manufacturing of printed electronics relies on the deposition of conductive liquid inks, typically onto polymeric or paper substrates. Among available conductive fillers for use in electronic inks, carbon nanotubes (CNTs) have high conductivity, low density, processability at low temperatures, and intrinsic mechanical flexibility. However, the electrical conductivity of printed CNT structures has been limited by CNT quality and concentration, and by the need for nonconductive modifiers to make the ink stable and extrudable. This study introduces a polymer‐free, printable aqueous CNT ink, and, via an ambient direct‐write printing process, presents the relationships between printing resolution, ink rheology, and ink‐substrate interactions. A model is constructed to predict printed feature sizes on impermeable substrates based on Wenzel wetting. Printed lines have conductivity up to 10 000 S m−1. The lines are flexible, with <5% change in DC resistance after 1000 bending cycles, and <3% change in DC resistance with a bending radius down to 1 mm. Demonstrations focus on i) conformality, via printing CNTs onto stickers that can be applied to curved surfaces, ii) interactivity using a CNT‐based button printed onto folded paper structure, and iii) capacitive sensing of liquid wicking into the substrate itself. Facile integration of surface mount components on printed circuits is enabled by the intrinsic adhesion of the wet ink.

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