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1. High Modulus, Strut-like poly(ether ether ketone) Aerogels Produced from a Benign Solvent

   https://doi.org/10.3390/gels10040283  

   Spiering, Glenn A; Godshall, Garrett F; Moore, Robert B (April 2024, Gels)

   Poly(ether ether ketone) (PEEK) was found to form gels in the benign solvent 1,3-diphenylacetone (DPA). Gelation of PEEK in DPA was found to form an interconnected, strut-like morphology composed of polymer axialites. To our knowledge, this is the first report of a strut-like morphology for PEEK aerogels. PEEK/DPA gels were prepared by first dissolving PEEK in DPA at 320 °C. Upon cooling to 50 °C, PEEK crystallizes and forms a gel in DPA. The PEEK/DPA phase diagram indicated that phase separation occurs by solid–liquid phase separation, implying that DPA is a good solvent for PEEK. The Flory–Huggins interaction parameter, calculated as χ12 = 0.093 for the PEEK/DPA system, confirmed that DPA is a good solvent for PEEK. PEEK aerogels were prepared by solvent exchanging DPA to water then freeze-drying. PEEK aerogels were found to have densities between 0.09 and 0.25 g/cm3, porosities between 80 and 93%, and surface areas between 200 and 225 m2/g, depending on the initial gel concentration. Using nitrogen adsorption analyses, PEEK aerogels were found to be mesoporous adsorbents, with mesopore sizes of about 8 nm, which formed between stacks of platelike crystalline lamellae. Scanning electron microscopy and X-ray scattering were utilized to elucidate the hierarchical structure of the PEEK aerogels. Morphological analysis found that the PEEK/DPA gels were composed of a highly nucleated network of PEEK axialites (i.e., aggregates of stacked crystalline lamellae). The highly connected axialite network imparted robust mechanical properties on PEEK aerogels, which were found to densify less upon freeze-drying than globular PEEK aerogel counterparts gelled from dichloroacetic acid (DCA) or 4-chlorphenol (4CP). PEEK aerogels formed from DPA were also found to have a modulus–density scaling that was far more efficient in supporting loads than the poorly connected aerogels formed from PEEK/DCA or PEEK/4CP solutions. The strut-like morphology in these new PEEK aerogels also significantly improved the modulus to a degree that is comparable to high-performance crosslinked aerogels based on polyimide and polyurea of comparable densities. 

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2. Increased strength in carbon-poly(ether ether ketone) composites from material extrusion with rapid microwave post processing

   https://doi.org/10.1016/j.addma.2022.103209  

   Ai, J-R; Li, S; Vogt, BD (October 2022, Additive manufacturing)

   One critical challenge for commercial products manufactured via material extrusion 3D printing is their inferior mechanical properties in comparison to injection molding; in particular, 3D printing leads to weaker properties perpendicular to the plane of the printed roads (z-direction). Here, rapid (≤20 s) post-processing of 3D printed carbon- poly(ether ether ketone) (PEEK) with microwaves is demonstrated to dramatically increase the modulus, such that the z-direction after microwave processing (2.7–3.8 GPa) exhibits a higher elastic modulus than the maximum in any direction for the as-printed part (2.3 GPa). Additionally, the stress at break in the z-orientation is increased by an order of magnitude by microwaves to slign with the stress for other print orientations in the as-printed state. The rapid heating and cooling by coupling of the microwave energy with the carbon filler in the PEEK does not increase the crystallinity of the PEEK, so the increased mechanical properties are attributed to improved interfaces between printed roads. This simple microwave post-processing enables large increases in the elastic modulus of the printed parts and can be tuned by the microwave power. As PEEK is generally difficult to print, these concepts can likely be applied to other commercial engineering plastic filaments that contain carbon or other fillers that are microwave active to rapidly post process 3D printed thermoplastics without requiring modification of the filament with selective placement of microwave absorbers. Additionally, these results demonstrate that the average crystallinity does not necessarily correlate with the strength of 3D printed semicrystalline plastics due to the importance of the details of the interface between adjacent printed roads. 

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3. Low-Temperature Plasmas Improving Chemical and Cellular Properties of Poly (Ether Ether Ketone) Biomaterial for Biomineralization

   https://doi.org/10.3390/ma17010171  

   Bradford, John P.; Hernandez-Moreno, Gerardo; Pillai, Renjith R.; Hernandez-Nichols, Alexandria L.; Thomas, Vinoy (January 2024, Materials)

   Osteoblastic and chemical responses to Poly (ether ether ketone) (PEEK) material have been improved using a variety of low-temperature plasmas (LTPs). Surface chemical properties are modified, and can be used, using low-temperature plasma (LTP) treatments which change surface functional groups. These functional groups increase biomineralization, in simulated body fluid conditions, and cellular viability. PEEK scaffolds were treated, with a variety of LTPs, incubated in simulated body fluids, and then analyzed using multiple techniques. First, scanning electron microscopy (SEM) showed morphological changes in the biomineralization for all samples. Calcein staining, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) confirmed that all low-temperature plasma-treated groups showed higher levels of biomineralization than the control group. MTT cell viability assays showed LTP-treated groups had increased cell viability in comparison to non-LTP-treated controls. PEEK treated with triethyl phosphate plasma (TEP) showed higher levels of cellular viability at 82.91% ± 5.00 (n = 6) and mineralization. These were significantly different to both the methyl methacrylate (MMA) 77.38% ± 1.27, ethylene diamine (EDA) 64.75% ± 6.43 plasma-treated PEEK groups, and the control, non-plasma-treated group 58.80 ± 2.84. FTIR showed higher levels of carbonate and phosphate formation on the TEP-treated PEEK than the other samples; however, calcein staining fluorescence of MMA and TEP-treated PEEK had the highest levels of biomineralization measured by pixel intensity quantification of 101.17 ± 4.63 and 96.35 ± 3.58, respectively, while EDA and control PEEK samples were 89.53 ± 1.74 and 90.49 ± 2.33, respectively. Comparing different LTPs, we showed that modified surface chemistry has quantitatively measurable effects that are favorable to the cellular, biomineralization, and chemical properties of PEEK. 

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4. ENABLING POLY ETHER ETHER KETONE AS A SOLID POLYMER ELECTROLYTE FOR STRUCTURAL BATTERY COMPOSITES

   https://doi.org/10.33599/nasampe/s.25.0168  

   Carrola, Mia; Asadi, Amir; Amiri, Ahmad; Yu, Zhenning; Koerner, Hilmar (January 2025, Society for the Advancement of Material and Process Engineering)

   To advance the state of structural battery composites, more mechanically robust polymeric materials must be investigated for use as the ionically conductive electrolyte. Currently, the matrices being utilized in solid polymer electrolytes lack mechanical strength, and are often gels, due to their amorphous structure offering increased lithium-ion conductivity. To address the need for more robust, semicrystalline polymer matrices, poly ether ether ketone (PEEK) was selected as a candidate that would offer both ionic conductivity and mechanical reinforcement in these novel multifunctional composite structures. Through a series of functionalization procedures, specifically sulfonation and lithiation of the polymer chains, the PEEK exhibits ionic conductivity and an amorphous microstructure. However, to maintain the structural characteristics required of the matrix, careful functionalization is used to tailor the PEEK electrolytes and strike a balance between the two inversely related properties (ion conductivity and crystallinity). It was found that selective adjusting of the morphology of the solid electrolyte successfully enables the two properties that are most important for this multifunctional application. The discoveries presented from this work provide a foundation to continue progress on thermoplastic structural battery composites. 

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5. Identifying the granitic composition water-saturated solidus

   Rufledt C, Thomas JB (September 2023, Xth Hutton Symposium)

   The granitic water-saturated solidus (G-WSS) is the lower temperature limit of magmatic mineral crystallization. The accepted water-saturated solidus for granitic compositions was largely determined >60 years ago1. More recent advances in experimental petrology, improved analytical techniques, and recent observations that granitic systems can remain active or spend a significant proportion of their lives at conditions below the traditional G-WSS2–5 necessitate a careful experimental investigation of the near-solidus regions of granitic systems. Natural and synthetic starting materials were melted at 10 kbar and 900°C with 48 wt% H2O to produce hydrous glasses for subsequent experiments at lower PT conditions used to locate the G-WSS. We performed crystallization experiments and melting experiments at temperatures ranging from 575 to 800°C and 1, 6, 8, and 10 kbar on 12 granitoid compositions. First, we ran a series of isothermal crystallization experiments along each isobar at progressively lower temperatures until runs completely crystallized to identify apparent solidus temperatures. Geochemical analyses of quenched glass compositions demonstrate that progressive crystallization drives all starting compositions towards silica-rich, water-saturated rhyolitic/granitic melts (e.g., ~7578 wt% SiO2). After identifying the apparent solidus temperatures at which the various compositions crystallized, we then ran series of reversal-type melting experiments. With the goal of producing rocks with hydrous equilibrium microstructures, we crystallized compositions at temperatures ~10°C below the apparent solidus identified in crystallization experiments, and then heated isobarically to conditions that produced ~20% melt during the crystallization experiments. Importantly, crystallization experiments and heating experiments at the same PT conditions produced similar proportions of melt, crystals, and vapor. A time-series of experiments 230 days at PT conditions previously identified to produce ~10% to 20% melt did not reveal any kinetic effects on melt crystallization. Experiments at 6 to 10 kbar crystallized/melted at temperatures close to the published G-WSS. However, at lower pressures where the published G-WSS is strongly curved in PT space, all compositions investigated contained melt to temperatures ~75 to 100°C below the accepted G-WSS. The similarity of crystallization temperatures for the higher-pressure experiments to previously published results, similar phase proportions in melting and crystallization experiments, and the lack of kinetic effects on crystallization collectively suggest that our lower pressure constraints on the G-WSS are accurate. The new experimental results demonstrating that the lower-pressure G-WSS is significantly lower than unanimously accepted estimates will help us to better understand the storage conditions, evolution, and potential for eruption in mid- to upper-crustal silicic magmatic systems. (1) Tuttle, O.; Bowen, N. Origin of Granite in the Light of Experimental Studies in the System NaAlSi3O8–KAlSi3O8–SiO2–H2O; Geological Society of America Memoirs; Geological Society of America, 1958; Vol. 74. https://doi.org/10.1130/MEM74. (2) Rubin, A. E.; Cooper, K. M.; Till, C. B.; Kent, A. J. R.; Costa, F.; Bose, M.; Gravley, D.; Deering, C.; Cole, J. Rapid Cooling and Cold Storage in a Silicic Magma Reservoir Recorded in Individual Crystals. Science 2017, 356 (6343), 1154–1156. https://doi.org/10.1126/science.aam8720. (3) Andersen, N. L.; Jicha, B. R.; Singer, B. S.; Hildreth, W. Incremental Heating of Bishop Tuff Sanidine Reveals Preeruptive Radiogenic Ar and Rapid Remobilization from Cold Storage. Proceedings of the National Academy of Sciences 2017, 114 (47), 12407–12412. https://doi.org/10.1073/pnas.1709581114. (4) Ackerson, M. R.; Mysen, B. O.; Tailby, N. D.; Watson, E. B. Low-Temperature Crystallization of Granites and the Implications for Crustal Magmatism. Nature 2018, 559 (7712), 94–97. https://doi.org/10.1038/s41586-018-0264-2. (5) Glazner, A. F.; Bartley, J. M.; Coleman, D. S.; Lindgren, K. Aplite Diking and Infiltration: A Differentiation Mechanism Restricted to Plutonic Rocks. Contributions to Mineralogy and Petrology 2020, 175 (4). https://doi.org/10.1007/s00410-020-01677-1. 

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