Simultaneous In-Film Polymer Synthesis and Self-Assembly for Hierarchical Nanopatterns

A key requirement for practical applications of nanostructured block copolymer (BCP) self-assembly is the ability to generate complex geometries including different shapes and diverse sizes across one substrate surface. This has been difficult because spatial control over the underlying chemistry of the BCP has been limited. Here, we demonstrate a photocontrolled in-film polymerization process in the presence of monomer vapor for synthesizing homopolymers in self-assembled BCP films. The homopolymers blend with BCPs and alter the nanopatterns by changing the underlying polymer chemistry and composition. We apply this technique to a variety of BCPs including polystyrene-b-polyisoprene-b-polystyrene, polystyrene-b-poly­(methyl methacrylate), and polystyrene-b-poly­(4-vinylpyridine). The region of in-film polymerization can be modulated by the location of irradiation using photomasks for obtaining distinct morphologies on one substrate, providing a new platform for hierarchically manipulating nanopatterns within the self-assembled BCP thin film as well as opening up a new area for radical polymerizations of monomers within such geometrically confined, swollen films

Multifunctional Carbon Fibers from Chemical Upcycling of Mask Waste

Over the past years, disposable masks have been produced in unprecedented amounts due to the COVID-19 pandemic. Their increased use imposes significant strain on current waste management practices including landfilling and incineration. This results in large volumes of discarded masks entering the environment as pollutants, and alternative methods of waste management are required to mitigate the negative effects of mask pollution. While current recycling methods can supplement conventional waste management, the necessary processes result in a product with downgraded material properties and a loss of value. This work introduces a simple method to upcycle mask waste into multifunctional carbon fibers through simple steps of thermal stabilization and pyrolysis. The pre-existed fibrous structure of polypropylene masks can be directly converted into carbonaceous structures with high degrees of carbon yield, that are inherently sulfur-doped, and porous in nature. The mask-derived carbon product demonstrates potential use in multiple applications such as for Joule heating, oil adsorption, and the removal of organic pollutants from aqueous environments. We believe that this process can provide a useful alternative to conventional waste management by converting mask waste generated during the COVID-19 pandemic into a product with enhanced value

Immobilization of Protease K with ZIF‑8 for Enhanced Stability in Polylactic Acid Melt Processing and Catalytic Degradation

Polylactic acid (PLA) is a biodegradable alternative to petroleum-based polymers for improving environmental sustainability of our society. However, the limited degradation rate and environmental conditions for PLA-based products remain significant challenges for their broader use in various applications. While Proteinase K (Pro K) from Tritirachium album has been demonstrated to efficiently degrade PLA, its autocatalytic degradation function in composite films is underexplored. Here, this work reports a strategy that encapsulates Pro K with zeolitic imidazole framework-8 (ZIF-8) in situ, combining a PLA matrix to prepare Pro K@ZIF-8/PLA films through solvent casting. The method is scalable and commercially viable, and the pH and thermal stability of the Pro K enzyme are significantly enhanced after immobilization. The enzyme can retain 61.8% of its initial activity after annealing at 160 °C for 10 min, allowing for its use in the melt processing of filler-containing PLA films. As a result, Pro K@ZIF-8/PLA films in buffer solutions exhibit stable degradation rates, which can be extended to PLA decomposition in acidic environments. Moreover, the enzyme in Pro K@ZIF-8/PLA films prepared by thermoforming remains active sufficiently to degrade PLA with a weight loss of up to 15% in 2 weeks. These results further indicate that our strategy can be broadly applicable for melt processing and controlled degradation of PLA materials with immobilized enzymes, allowing for its transformative impact for promoting environmental sustainability

Morphology Control in Mesoporous Carbon Films Using Solvent Vapor Annealing

Ordered mesoporous (2–50 nm) carbon films were fabricated using cooperative self-assembly of a phenolic resin oligomer with a novel block copolymer template (poly­(styrene-<i>block</i>-<i>N</i>,<i>N</i>-dimethyl-<i>n</i>-octadecylamine <i>p</i>-styrenesulfonate), (PS-<i>b</i>-PSS-DMODA)) synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization. Due to the high <i>T</i>_g of the PS segment and the strong interactions between the phenolic resin and the PSS-DMODA, the segmental rearrangement is kinetically hindered relative to the cross-linking rate of the phenolic resin, which inhibits long-range ordering and yields a poorly ordered mesoporous carbon with a broad pore size distribution. However, relatively short exposure (2 h) to controlled vapor pressures of methyl ethyl ketone (MEK) yields significant improvements in the long-range ordering and narrows the pore size distribution. The average pore size increases as the solvent vapor pressure during annealing increases, but an upper limit of <i>p</i>/<i>p</i>₀ = 0.85 exists above which the films dewet rapidly during solvent vapor annealing. This approach can be extended using mesityl oxide, which has similar solvent qualities to MEK, but is not easily removed by ambient air drying after solvent annealing. This residual solvent can impact the morphology that develops during cross-linking of the films. These results illustrate the ability to fine-tune the mesostructure of ordered mesoporous carbon films through simple changes in the processing without any compositional changes in the initial cast film

Accelerated Synthesis of Ordered Mesoporous Carbons Using Plasma

Conventional ordered mesoporous carbon (OMC) production usually requires long processing times in the carbonization step to achieve desired temperatures through controlled ramps. To enable expedited materials discovery, developing advanced manufacturing capability with significantly improved throughput is highly desired. Current approaches for accelerating the synthesis of OMCs include using microwave and Joule heating. However, both methods rely on the introduction of additional components, such as microwave absorbers and electrically conductive agents, within the bulk materials to impart the ability to reach high carbonization temperatures. This work demonstrates accelerated synthesis and functionalization of OMCs through the use of a dielectric barrier discharge plasma, where carbonization can be accomplished within 15 min using 30 W plasma sources, representing more than an order of magnitude increase in polymer-to-carbon conversion kinetics compared to that of a traditionally pyrolyzed analogue. Particularly, the ability of performing rapid carbonization without the use of additional substrates within the OMC precursor systems is advantageous. A systematic investigation of how plasma power, time, and gas atmosphere impact the resulting OMC pore textures and properties is performed, demonstrating the broad applicability of plasma-enabled carbonization methods. Furthermore, we demonstrate that the plasma treatment strategy can be extended to incorporate heteroatoms into the carbon framework by introducing ammonia gas, resulting in OMCs with a nitrogen content up to 4.7 at %, as well as non-Pluronic templating systems for synthesizing OMC with pore sizes larger than 10 nm. As employing a plasma source for materials pyrolysis is an industrially relevant approach, our system can be extended toward scaled synthesis of OMCs with much faster production rates

Control of Ordering and Structure in Soft Templated Mesoporous Carbon Films by Use of Selective Solvent Additives

The structure of ordered mesoporous carbons fabricated using poly­(styrene-block-<i>N</i>,<i>N</i>,-dimethyl-<i>n</i>-octadecylamine <i>p</i>-styrenesulfonate) (PS-<i>b</i>-PSS-DMODA) as the template and phenolic resin (resol) as the carbon source can be easily manipulated by inclusion of low concentrations of low volatility selective solvents in the casting solution. Casting from neat methyl ethyl ketone yields a disordered structure even upon thermal annealing. However, addition of both dioctyl phthalate (DOP, PS selective) and dimethyl sulfoxide (DMSO, resol and PSS-DMODA selective) at modest concentrations to this casting solution provides sufficient mobility to produce highly ordered films with cylindrical mesopores. The DOP acts to swell the hydrophobic domain and can more than double the mesopore size, while the DMSO acts to swell the resol phase. Moreover, the surface area of the mesoporous carbons increases significantly as the meosopore size increases. This is a result of the decrease in wall thickness, which can be ascertained by the constant <i>d</i>-spacing of the mesostructure as the pore size increases. This behavior is counter to the typical effect of pore swelling agents that increase the pore size and decrease the surface area. Moreover, with only 4 wt % DOP/DMSO in the solution (20 wt % relative to solids), the scattering profiles exhibit many orders of diffraction, even upon carbonization, which is not typically observed for soft templated films. Variation in the concentration of DOP and DMSO during casting enables facile tuning of the structure of mesoporous carbon films

Ambient Drying Route to Aramid Nanofiber Aerogels with High Mechanical Properties for Low‑<i>k</i> Dielectrics

Polymeric aerogels with low dielectric constant (low-k) are an important material solution for applications in high-frequency terminal electronic devices. However, most aerogels are prepared using high-cost supercritical drying or freeze-drying methods and typically exhibit poor mechanical properties and low thermal stability, which limits their use in practical applications. Here, we report the fabrication of aerogels with layered structure and hierarchical nanopores based on aramid nanofibers (ANFs), using a vacuum-assisted filtration method followed by low-cost ambient drying. The porosity of the ANF aerogels can be controlled from 38 to 79% by rationally selecting solvents with different surface tension for solvent exchange, tuning the affinity between solvents and ANF skeletons as well as controlling the solvent evaporation rate during the ambient drying process. The ANF aerogels have an ultralow and tunable dielectric constant as low as 1.56 while exhibiting a low dielectric loss between 0.0040 to 0.0055 at 1 MHz. The advantageous low-k property can be preserved at high temperatures up to 300 °C, and an inherent flame retardancy is achieved due to the rigid and all-aromatic backbone structure of poly­(p-phenylene terephthalamide). Moreover, the nanoporous ANF layers with relatively lower porosity compared with the overall porosity of the aerogel provide strong mechanical strength and modulus, while the presence of larger nanopores from the interspacing of ANF layers ensures a high porosity for the entire aerogel, which endows the aerogel film with superior tensile strength and modulus compared with their conventional counterparts containing homogeneous porous structures. Collectively, these ANF aerogels exhibit low-k, outstanding mechanical properties, high thermal stability, and inherent flame retardancy, enabling them to become very promising next-generation dielectric materials

Nanoporous Nonwoven Fibril-Like Morphology by Cooperative Self-Assembly of Poly(ethylene oxide)-<i>block</i>-Poly(ethyl acrylate)-<i>block</i>-Polystyrene and Phenolic Resin

Cooperative self-assembly of block copolymers with (in)­organic precursors effectively generates ordered nanoporous films, but the porosity is typically limited by the need for a continuous (in)­organic phase. Here, a network of homogeneous fibrous nanostructures (≈20 nm diameter cylinders) having high porosity (≈ 60%) is fabricated by cooperative self-assembly of a phenolic resin oligomer (resol) with a novel, nonfrustrated, ABC amphiphilic triblock copolymer template, poly­(ethylene oxide)-<i>block</i>-poly­(ethyl acrylate)-<i>block</i>-polystyrene (PEO-<i>b</i>-PEA-<i>b</i>-PS), via a thermally induced self-assembly process. Due to the high glass transition temperature (<i>T</i>_g) of the PS segments, the self-assembly behavior is kinetically hindered as a result of competing effects associated with the ordering of the self-assembled system and the cross-linking of resol that suppresses segmental mobility. The balance in these competing processes reproducibly yields a disordered fibril network with a uniform fibril diameter. This nonequilibrium morphology is dependent on the PEO-<i>b</i>-PEA-<i>b</i>-PS to resol ratio with an evolution from a relatively open fibrous structure to an apparent poorly ordered mixed lamellae-cylinder morphology. Pyrolysis of these former films at elevated temperatures yields a highly porous carbon film with the fibril morphology preserved through the carbonization process. These results illustrate a simple method to fabricate thin films and coatings with a well-defined fiber network that could be promising materials for energy and separation applications

Ambient Drying Route to Aramid Nanofiber Aerogels with High Mechanical Properties for Low‑<i>k</i> Dielectrics

Polymeric aerogels with low dielectric constant (low-k) are an important material solution for applications in high-frequency terminal electronic devices. However, most aerogels are prepared using high-cost supercritical drying or freeze-drying methods and typically exhibit poor mechanical properties and low thermal stability, which limits their use in practical applications. Here, we report the fabrication of aerogels with layered structure and hierarchical nanopores based on aramid nanofibers (ANFs), using a vacuum-assisted filtration method followed by low-cost ambient drying. The porosity of the ANF aerogels can be controlled from 38 to 79% by rationally selecting solvents with different surface tension for solvent exchange, tuning the affinity between solvents and ANF skeletons as well as controlling the solvent evaporation rate during the ambient drying process. The ANF aerogels have an ultralow and tunable dielectric constant as low as 1.56 while exhibiting a low dielectric loss between 0.0040 to 0.0055 at 1 MHz. The advantageous low-k property can be preserved at high temperatures up to 300 °C, and an inherent flame retardancy is achieved due to the rigid and all-aromatic backbone structure of poly­(p-phenylene terephthalamide). Moreover, the nanoporous ANF layers with relatively lower porosity compared with the overall porosity of the aerogel provide strong mechanical strength and modulus, while the presence of larger nanopores from the interspacing of ANF layers ensures a high porosity for the entire aerogel, which endows the aerogel film with superior tensile strength and modulus compared with their conventional counterparts containing homogeneous porous structures. Collectively, these ANF aerogels exhibit low-k, outstanding mechanical properties, high thermal stability, and inherent flame retardancy, enabling them to become very promising next-generation dielectric materials

Unidirectional Alignment of Block Copolymer Films Induced by Expansion of a Permeable Elastomer during Solvent Vapor Annealing

One challenge associated with the utilization of block copolymers in nanotechnology is the difficulties associated with alignment and orientation of the self-assembled nanostructure on macroscopic length scales. Here we demonstrate a simple method to generate unidirectional alignment of the cylindrical domains of polystyrene-block-polyisoprene-block-polystyrene, SIS, based on a modification of the commonly utilized solvent vapor annealing (SVA) process. In this modification, cross-linked poly­(dimethylsiloxane) (PDMS) is physically adhered to the SIS film during SVA; differential swelling of the PDMS and SIS produces a shear force to align the ordered domains of SIS in the areas covered by PDMS. This method is termed solvent vapor annealing with soft shear (SVA-SS). The alignment direction can be readily controlled by the shape and placement of the PDMS with the alignment angle equal to the diagonal across the rectangular PDMS pad due to a propagating deswelling front from directional drying of the PDMS by a dry air stream. Herman’s (second order) orientational parameter, S, can quantify the quality of the alignment over large areas with S > 0.94 obtainable using SVA-SS