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1. Photoinitiator-grafted polymer chains for integrating hydrogels with various materials

   https://doi.org/10.1016/j.xcrp.2021.100463  

   Yin, Tenghao; Lavoie, Shawn R.; Qu, Shaoxing; Suo, Zhigang (June 2021, Cell Reports Physical Science)

   Hydrogels are commonly integrated with other materials. In the one-pot synthesis of a hydrogel coating, polymerization, crosslink, and interlink are concurrent. This concurrency, however, is often inapplicable for integrating hydrogels to other materials. For example, a permeable substrate will absorb small molecules in the solution, causing side reactions and even toxicity. Here, we report a method to break the concurrency by using photoinitiator-grafted polymer chains (PGPCs). A type of photoinitiator is copolymerized with various monomers. The PGPCs are uncrosslinked during syn- thesis, have long shelf lives in dark storage, and can be applied to a substrate by brush, cast, spin, dip, spray, or print. Under ultraviolet light, the polymer chains crosslink into a network and interlink with the substrate. The cured PGPC hydrogels are characterized by me- chanical tests. Furthermore, the PGPCs are demonstrated to adhere wet materials, form hydrophilic coatings on hydrophobic substrates, and pattern functional groups on permeable substrates. 

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2. Ab Initio Emulsion Atom‐Transfer Radical Polymerization

   https://doi.org/10.1002/anie.201804647  

   Lorandi, Francesca; Wang, Yi; Fantin, Marco; Matyjaszewski, Krzysztof (May 2018, Angewandte Chemie International Edition)

   Abstract Stable latexes of poly(meth)acrylates with predetermined molecular weights, narrow molecular‐weight distributions, and controlled architecture were prepared by true ab initio emulsion atom‐transfer radical polymerization. Water‐soluble (macro)initiators in combination with a hydrophilic catalyst, Cu/tris(2‐pyridylmethyl)amine, initiated the polymerization in the aqueous phase. The catalyst strongly interacted with the surfactant sodium dodecyl sulfate (SDS), thereby tuning the polymerization within nucleated hydrophobic polymer particles. Long‐term stable latexes were obtained, even with SDS loading below 3 wt % relative to monomer. Block and gradient copolymers were prepared in situ. The reaction volume and solid content were successfully increased to 100 mL and 40 vol %, respectively, thus suggesting facile scale‐up of this technique. The proposed setup could be integrated in existing industrial plants used for emulsion polymerization. 

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3. Robust silane self-assembled monolayer coatings on plasma-engineered copper surfaces promoting dropwise condensation

   https://doi.org/10.1016/j.ijheatmasstransfer.2022.123028  

   Wang, Ruisong; Guo, Jiahui; Muckleroy, Emily A; Antao, Dion S (September 2022, International Journal of Heat and Mass Transfer)

   Dropwise condensation is well known to result in better heat transfer performance owing to efficient condensate/droplet removal, which can be harnessed in various industrial heat/mass transfer applications such as power generation and conversion, water harvesting/desalination, and electronics thermal management. The key to enhancing condensation via the dropwise mode is thin low surface energy coatings (<100 nm) with low contact angle hysteresis. Ultrathin (<5 nm) silane self assembled monolayers (or SAMs) have been widely studied to promote dropwise condensation due to their minimal thermal resistance and scalable integration processes. Such thin coatings typically degrade within an hour during condensation of water vapor. After coating failure, water vapor condensation transitions to the inefficient filmwise mode with poor heat transfer performance. We enhance silane SAM quality and durability during water vapor condensation on copper compared to state of the art silane coatings on metal surfaces. We achieve this via (i) surface polishing to sub-10 nm levels, (ii) pure oxygen plasma surface treatment, and (iii) silane coating integration with the copper substrate in an anhydrous/moisture-free environment. The resulting silane SAM has low contact angle hysteresis (≈20°) and promotes efficient dropwise condensation of water for >360 hours without any visible sign of coating failure/degradation in the absence of non condensable gases. We further demonstrate enhanced heat transfer performance (≈5 7× increase over filmwise condensation) over an extended period of time. Surface characterization data post-condensation leads us to propose that in the absence of non-condensable gases in the vapor environment, the silane SAM degrades due to reduction and subsequent dissolution of copper oxide at the oligomer-substrate interface. The experiments also indicate that the magnitude of surface subcooling (or condensation rate) affects the rate of coating degradation. This work identifies a pathway to durable dropwise promoter coatings that will enable efficient heat transfer in industrial applications. 

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4. Solvent-Free Reactive Vapor Deposition for Functional Fabrics: Separating Oil–Water Mixtures with Fabrics

   https://doi.org/10.3390/fib7010002  

   Cheng, Nongyi; Park, Kwang-Won; Andrew, Trisha L. (January 2019, Fibers)

   A facile, solvent-minimized approach to functionalize commercial raw fabrics is described. Reactive vapor deposition of conjugated polymers followed by post-deposition functionalization transforms common, off-the-shelf textiles into distinctly hydrophobic or superhydrophilic materials. The fabric coatings created by reactive vapor deposition are especially resistant to mechanical and solvent washing, as compared to coatings applied by conventional, solution-phase silane chemistries. Janus fabrics with dissimilar wettability on each face are also easily created using a simple, three-step vapor coating process, which cannot be replicated using conventional solution phase functionalization strategies. Hydrophobic fabrics created using reactive vapor deposition and post-deposition functionalization are effective, reusable, large-volume oil–water separators, either under gravity filtration or as immersible absorbants. 

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5. Universal salt-assisted assembly of MXene from suspension on polymer substrates

   https://doi.org/10.1038/s41467-024-53840-y  

   Zhao, Liang; Bi, Lingyi; Hu, Jiayue; Gao, Guanhui; Zhang, Danzhen; Li, Yun; Flynn, Aidan; Zhang, Teng; Wang, Ruocun; Cheng, Xuemei_M; et al (November 2024, Nature Communications)

   Abstract Two-dimensional carbides and nitrides, known as MXenes, are promising for water-processable coatings due to their excellent electrical, thermal, and optical properties. However, depositing hydrophilic MXene nanosheets onto inert or hydrophobic polymer surfaces requires plasma treatment or chemical modification. This study demonstrates a universal salt-assisted assembly method that produces ultra-thin, uniform MXene coatings with exceptional mechanical stability and washability on various polymers, including high-performance polymers for extreme temperatures. The salt in the Ti₃C₂T_xcolloidal suspension reduces surface charges, enabling electrostatically hydrophobized MXene deposition on polymers. A library of salts was used to optimize assembly kinetics and coating morphology. A 170 nm MXene coating can reduce radiation temperature by ~200 °C on a 300 °C PEEK substrate, while the coating on Kevlar fabric provides comfort in extreme conditions, including outer space and polar regions. 

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