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This paper experimentally investigates adhesive fracture resistance and crack path selection in adhesive joints containing well-defined localized interfacial defects. Several systematic patterns of localized interfacial defects were created on base-acid treated aluminum adherends by physical vapor deposition of copper through a mask. Adhesive joints were prepared using a commercially available, structural epoxy adhesive and the effect of localized interface defects on the performance of adhesive joints was studied. Under mode-I loading conditions, the presence of localized weak interfaces influenced the fracture energy of a propagating debond over a considerable distance. For a crack tip approaching a given weak interface pattern, a falling or reverse R-curve type trend was observed. Within the same DCB specimen, as the crack tip advanced beyond the patterned region, a rising R-curve type trend was observed as fracture energy increased with increasing crack lengths, which were recorded visually and were also inferred using compliance and crack length relationship. In addition, the mode-I fracture energy was found to scale with the area fraction of the weak interfaces according to a rule of mixtures. For the adhesive system and the joint geometry used in this study, it was observed that cohesive failure in the adhesive layer can be obtained even in the presence of exceptionally weak interfaces (similar in size to those detected in mode-I loading) when loaded under mixed mode conditions (achieved through asymmetric loading of DCB-like specimens), that tended to steer the crack away from the interface. When loaded with the opposite mode mixity direction, the crack tip propagated through the defects, though the fracture energy did not exhibit similar R-curve type trends as observed in mode-I tests. The results offer insights into the interaction of propagating cracks in adhesive layers and their interactions with discrete, localized defects, which could lead to improvements in surface preparations and bond integrity or even to joint designs having intentionally placed defects useful in controlled disassembly or for other purposes. [ABSTRACT FROM AUTHOR]

Ionomer chain and solvent molecule interactions during solution-casting, solvent evaporation, and solidification impacts chain entanglements, spatial arrangement of functional groups, microstructure development, morphology, and physical properties. These concepts were investigated using poly( t -butylstyrene- b -ethylene- alt -propylene- b -sulfonatedstyrene- b -ethylene- alt -propylene- b - t -butylstyrene) with a fixed ion-exchange capacity of 1.0, and estimated solubility parameter of 21.8 (J/cm 3 ) 1/2 . Films were solution-cast using an equal volume cyclohexane:heptane mixture (C:H), chloroform (CHCl 3 ), and tetrahydrofuran (THF). Subsequent film structures were evaluated using transmission electron microscopy (TEM), small-angle X-ray scattering (SAXS), FT-IR, and electrochemical impedance spectroscopy. A commercially supplied film had sulfonated domains randomly distributed throughout it, and its initial proton conductivity was 11.8 mS/cm. A film created by solution-casting from C:H had a morphology containing randomly distributed sulfonated domains. This random morphology became more ordered with a lamella-like morphology when solution-cast using THF. The film produced from CHCl 3 had a morphology that was between random and ordered. Film morphology differences were attributed to a poorer solvent system that inhibited chain solvation. The solution-cast film’s proton conductivity was 1.0 mS/cm for a random morphology, and 15.3 mS/cm with a lamella-like structure. Increasing the ionomer-THF solution-casting temperature to 40 °C produced a film with a 103% increase in conductivity (31.2 mS/cm). This led to a water uptake change from 29 wt% to 80 wt%. Cycling a THF solution-cast film from its dry to a wet state revealed that a lamella-like morphology would maintain its conductivity, but the commercial film’s conductivity decreased from 11.8 mS/cm to 0.98 mS/cm. Ionomer film properties were found to be dependent upon solvent quality and processing. [ABSTRACT FROM AUTHOR]

The phase diagram for the thermoreversible gelation of poly(ether ether ketone) (PEEK) in dichloroacetic acid (DCA) was constructed over broad temperature and concentration ranges, revealing that PEEK is capable of dissolving and forming gels in DCA up to a weight fraction of 25 wt%. For PEEK solutions within this concentration range, the time required for gelation decreased with increasing temperature up to 80 °C, above which the gelation time increased considerably. Highly porous aerogels of PEEK were prepared through simple solvent exchange and lyophilization of the PEEK/DCA gels. Aerogel density was controlled by varying the PEEK concentration in solution, and shown to be unaffected by PEEK molecular weight (MW). Annealing PEEK aerogels prepared from relatively low concentration gels resulted in aerogels of increased density. Mechanical properties (in compression) were shown to improve with increasing density, resulting in equivalent compressive moduli at comparable density regardless of preparation method (concentration variation or annealing parameters). Additionally, density-matched aerogels from various MW PEEK showed a correlation between increasing MW and increasing compressive modulus. Contact angle and contact angle hysteresis revealed that PEEK aerogels have a high contact angle, suggesting superhydrophobicity, that decreases with increasing density and a very low contact angle hysteresis that increases with increasing density. [ABSTRACT FROM AUTHOR]

Tris- and tetra-(β-alanine)-grafted polyisobutylenes ( A3 and A4 ) with the same grafting density have been synthesized and studied. IR, DSC, SAXS, and WAXD show that the β-alanine tetramer segments in A4 form β-sheet crystals similar to those in A3 . A3 and A4 are melt-processable TPEs. The less than 5% by volume of β-sheet crystals in A3 and A4 bring about mechanical properties significantly better that those of a vulcanized butyl rubber composite optimally reinforced with carbon black ( CBV ). A4 is somewhat stiffer and less extensible than A3 . Overall, only a small gain in toughness is achieved for A4 over A3 . Importantly, A3 and A4 also show hysteretic properties and dynamic mechanical properties superior to CBV . Both A3 and A4 are less hysteretic than CBV at low strains and more hysteretic at high strains. Their loss factors are substantially lower than that of CBV in the temperature range of 60–100 °C, and their modulus dependence on strain amplitude at very low strains (Payne effect) are significantly subdued in comparison to CBV . In fact, A3 is slightly better than A4 in all respects from the view point of hysteresis and dynamic mechanical properties. Dichroic IR study indicates that the oligo(β-alanine) segments in A3 and A4 statistically prefer to orient perpendicular to the extension axis due to shear stress exerted on the elongated β-sheet crystals at <250% strain. At higher strains, the grafting molecular architecture and the random location of the load-bearing chain on the surface of the β-sheet crystals dictate the orientation of the β-sheet crystals to be random. No fragmentation of the β-sheet crystals in the hydrogen-bonding direction is detectable during the entire process of extension until break. The residual preference of the oligo(β-alanine) segments for the orientation perpendicular to the extension axis is attributed to the elongated β-sheet crystal morphology, which prevent the crystals from fully comply to the load-bearing chains. [ABSTRACT FROM AUTHOR]

Multiblock copolymers of poly(arylene ether sulfones) (PAESs) and poly(1,4-cyclohexylenedimethylene terephthalate) (PCT) were synthesized via melt-phase polymerization. PAES oligomers (M n = 2000 g/mol) were synthesized with hydroxyethoxyl end groups, and then reacted with dimethyl terephthalate (DMT) and 1,4-cyclohexanedimethanol (CHDM) to obtain segmented copolymers with the goal of introducing semi-crystallinity into the PAES segmented block copolymers. Two CHDMs ( all trans and cis/trans = 30/70) were used for comparison. Weight percentages of PCT segments varied from 20 wt% to 80 wt%. According to the results measured by DSC, DMA and WAXS, the copolymers crystallized when the content of PCT segment was above 50 wt%, and the crystallinity of the copolymers exhibited a proportional dependence on the weight percentage of PCT segments. Segmented copolymers with trans -CHDM as the polyester segment exhibited a higher level of crystallinity than the 30/70 CHDM mixture. [ABSTRACT FROM AUTHOR]

Crystallization inhibitors in amorphous solid dispersions (ASD) enable metastable supersaturated drug solutions that persist for a physiologically relevant time. Olefin cross-metathesis (CM) has successfully provided multifunctional cellulose-based derivatives as candidate ASD matrix polymers. In proof of concept studies, we prepared hydrophobic bile salt/cellulose adducts by CM with naturally occurring bile salts. We hypothesized that increased hydrophilicity would enhance the ability of these conjugates to maximize bioactive supersaturation. Their selective preparation presents a significant synthetic challenge, given polysaccharide reactivity and polysaccharide and bile salt complexity. We prepared such derivatives using a more hydrophilic hydroxypropyl cellulose (HPC) backbone, employing a pent-4-enyl tether (Pen) for appending bile acids. We probed structure-property relationships by varying the nature and degree of substitution of the bile acid substituent (lithocholic or deoxycholic acid). These conjugates are indeed synergistic inhibitors, as demonstrated with the fast-crystallizing prostate cancer drug, enzalutamide. The lithocholic acid methyl ester derivative, AcrMLC-PenHHPCPen (0.64), increased induction time 68 fold vs. drug alone. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Polymer tubes with control on tube thickness and surface morphology are highly desirable for a wide range of applications in energy storage and transport as well as in tissue engineering and drug delivery. In this work, using the non-electrospinning Spinneret based Tunable Engineered Parameters (STEP) platform, we demonstrate fabrication of long (mm-cm) aligned polystyrene (PS) nano and microscale tubes in single and multiple layers. The tube outer diameters (0.3–3.6 μm), surface morphologies (pore size distribution: 20–200 nm) and tube wall thickness (50–500 nm) are controlled through tuning of the relative humidity, solvent type, and solution concentration (C/C*∼12). We experimentally show that incorporating MWCNTs into the tube structure significantly increases their ultimate strength and elongation. The tubes are also capable of sustaining high compressive radial pressures (0.2–0.6 MPa). When used as absorbents for oil cleaning, crisscross layers of porous PS tubes demonstrate higher absorption capacity compared with solid PS fibres (20–30% enhancement) and polypropylene (PP) fibres (90–110% enhancement). [Copyright &y& Elsevier]

Segmented polyurethanes based on polytetramethylene glycol (PTMG) of 1000 g/mol were synthesized using a two-step polymerization procedure. Various hard segments were obtained using hexamethylene diisocyanate (HDI) or 4,4′-methylenebis(phenyl isocyanate) (MDI) as the diisocyanates and hydroquinone bis(2-hydroxyethyl)ether (HQEE) or triptycene-1,4-hydroquinone bis(2-hydroxyethyl)ether (TD) as the chain extenders. The effect of rigidity and bulkiness of the hard segments on morphology, thermal and mechanical properties were studied. Fourier transform infrared (FTIR) suggested that hydrogen bonding interactions were weakened in the presence of the bulky triptycene-containing hard segments. Variable temperature FTIR demonstrated that hydrogen bonds completely dissociate at around 170 °C for polyurethanes chain extended by HQEE compared to around 110 °C for their TD analogs. Polyurethanes from MDI and TD displayed microphase mixing behavior based on atomic force microscopy (AFM) and small angle X-ray scattering (SAXS). When HDI was used as the diisocyanate in the TD chain extended polyurethane, enhanced microphase separation was observed with comparable mechanical properties to those of the MDI analogs with HQEE. [ABSTRACT FROM AUTHOR]

Abstract: A series of multiblock copolymers based upon alternating segments of a hydrophilic disulfonated poly(arylene ether sulfone) and a hydrophobic fluorine-terminated poly(arylene ether benzonitrile) (6FPAEB) were synthesized and characterized for use as proton exchange membranes (PEM). The ion-exchange capacity of the block copolymers were varied by utilizing 4,4′-biphenol or hydroquinone in combination with 3,3′-disulfonated-4,4′-dichlorodiphenyl sulfone (SDCDPS) to form the hydrophilic segments. The alternating block copolymer morphology was achieved by using mild temperatures to link the oligomers together and minimize ether–ether interchange reactions. Both the 4,4′-biphenol and hydroquinone based membranes showed high proton conductivity with moderate water uptake and good mechanical properties. The block copolymers displayed nanophase separated morphologies, confirmed by transmission electron microscopy (TEM) and small angle x-ray scattering (SAXS). The strong membrane performance was attributed to the multi-phase morphology. [Copyright &y& Elsevier]

Abstract: An unprecedented family of segmented polydimethylsiloxane poly(urea oxamide) (PDMS-UOx) copolymers displayed thermoplastic elastomeric behavior with improved thermomechanical properties compared to PDMS polyurea (PDMS-U) analogs. A two-step, PDMS end-capping sequence using diethyl oxalate and hydrazine generated difunctional oxamic hydrazide capped oligomers. Polymerization with HMDI provided high molecular weight copolymers, which yielded elastomeric films with monodisperse hard segments. Dynamic mechanical analysis (DMA) of PDMS-UOx copolymers revealed a broad, rubbery plateau that extended for >180 °C. The PDMS-UOx service window extended ∼120 °C further than a PDMS-U analog, presumably due to enhanced hydrogen bonding and concomitant microphase separation. DSC and WAXD elucidated the amorphous morphology of PDMS-UOx, and DMA, SAXS, and AFM confirmed a well-defined microphase-separated morphology. Incorporation of urea oxamide groups significantly affected microphase separation and thermomechanical properties, and these copolymers offer impact in adhesive and biomedical technologies due to low temperature reaction conditions for unique hydrogen bond containing segmented copolymers. [Copyright &y& Elsevier]

Abstract: Adenine-functionalized ionenes (ionene-A) and thymine-functionalized ionenes (ionene-T) were synthesized from novel nucleobase-containing monomers from an efficient aza-Michael addition to an acrylate precursor. Complexes of ionenes with nucleobase-containing guest molecules (n-butyl thymine, nBT and n-butyl adenine, nBA) exhibited well-defined complementary hydrogen bonding interactions. Job’s analysis revealed a 1:1 stoichiometry for the hydrogen-bonded complexes of [ionene-A]:[nBT], [ionene-T]:[nBA], and [nBA]:[nBT]. A mathematical fit of the chemical shifts to the Benesi–Hildebrand method revealed the association constants of 94M−1, 130M−1, and 137M−1 for complexes of [ionene-A]:[nBT], [ionene-T]:[nBA], and [nBA]:[nBT], respectively. Furthermore, DSC thermograms of 1:1 [ionene-A/T]:[guest molecule] complexes showed the disappearance of the melting transition for the guest molecule, confirming the absence of macrophase separation of the nucleobase guest in the polymer matrix. Morphological studies including atomic force microscopy (AFM) and small-angle X-ray scattering (SAXS) revealed a microphase-separated morphology for the nucleobase-containing ionenes and less defined microphase separation for the 1:1 complexes. [Copyright &y& Elsevier]

Abstract: A semi-continuous process using scCO2 is reported for processing polymer–clay composites with high clay loading (i.e. 10wt %) by reducing the collapse of the exfoliated clays. Two major modifications are involved in the new procedure: exfoliating the nano-clay directly into the hopper filed with pellets followed by processing the composite immediately and sequentially mixing the clay into the melt. This latter approach helped to minimize the clay collapse when processing the composites with high clay loadings. Transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD) results are provided to investigate the effect of sequential mixing on reducing the clay collapse in the nanocomposite. Surface modified montmorillonite (MMT) nano-clay/polypropylene (PP) composite at 10wt % nano-clay with improved clay dispersion was obtained with increased modulus and tensile strength of 63 % and 16%, respectively, compared to the pure PP matrix. [Copyright &y& Elsevier]

Abstract: Poly(ethylene glycol) (PEG)-based sulfonated polyurethanes bearing either sulfonated soft segments (SSSPU) or sulfonated hard segments (SHSPU) were synthesized using sulfonated monomers. Differential scanning calorimetry (DSC) revealed that sulfonate anions either in the soft segments or hard segments both increased the glass transition temperatures (T g’s) of the soft segments and suppressed their crystallization. Moreover, dynamic mechanical analysis (DMA) and tensile analysis demonstrated that SSSPU possessed a higher modulus and tensile strength relative to SHSPU. Fourier transform infrared (FTIR) spectroscopy revealed that hydrogen bonding interactions in SHSPU were suppressed compared to SSSPU and noncharged PU. This observation suggested a high level of phase-mixing for SHSPU. In addition, atomic force microscopy (AFM) phase images revealed that both SSSPU and noncharged PU formed well-defined microphase-separated morphologies, where the hard segments phase-separated into needle-like hard domains at the nanoscale. However, SHSPU showed a phase-mixed morphology, which was attributed to increased compatibility of polar PEG soft segments with sulfonated ionic hard segments and disruption of hydrogen bonds in the hard segment. The phase-mixed morphology of SHSPU was further demonstrated using small angle X-ray scattering (SAXS), which showed a featureless X-ray scattering profile. In contrast, SAXS profiles of SSSPU and noncharged PU demonstrated microphase-separated morphologies. Moreover, SSSPU also displayed a broad ionomer peak ranging in q = 1–2 nm−1, which resulted from the sodium sulfonate ion pair association in the polar PEG soft phase. Morphologies of sulfonated polyurethanes correlated well with thermal and mechanical properties. [Copyright &y& Elsevier]

Abstract: The isolation and assessment of hydrocarbonoclastic bacteria often represents a key strategy in the bioremediation of hydrocarbon-contaminated sites. However the isolation and assessment of such bacteria is often a lengthy and expensive procedure. The aim of this study was to identify potential isolates for use in the remediation of hydrocarbon contaminated sites using a combination of selective isolation plating, the Biolog system and subsequent multivariate analyses. The use of weathered oil as the main C source restricted the number of isolates growing to 5×102 CFUg soil−1. Isolates (n=96) were then assessed individually using Biolog MT2 plates with seven different hydrocarbons (dodecane, tridecane, hexadecane, octadecane, eicosane, naphthalene and phenanthrene). The results indicated that all isolates were able to grow on at least one hydrocarbon from the seven chosen. This confirmed that the isolation media developed was selective in isolating hydrocarbonoclastic bacteria only. Cluster analysis of Biolog data separated the isolates into two discrete clusters with cluster 2 identifying hydrocarbonoclastic bacteria that are effective in degrading a variety of contaminants. Further study on the isolates from cluster 2 was carried out based on their phylogenetic analysis. Phylogenetic analysis of 28 bacterial isolates from cluster 2 based on the 1500bp sequences from 16S rDNA genes using MRBAYES confirmed all isolates as being hydrocarbonoclastic, providing supportive evidence that isolates from cluster 2 have a potential use in bioremediation. This approach could improve both the speed and efficiency of the commercial bioremediation process. [Copyright &y& Elsevier]

Abstract: The effects of block length and solution-casting conditions on the final microstructures and properties of disulfonated poly(arylene ether sulfone) multiblock copolymer (BPSH100–BPS0) films for proton exchange membranes were investigated based on the basic principles of microstructure formation of block copolymers. Morphological studies using transmission electron microscopy and small angle X-ray scattering demonstrated that as the block length increased, the inter-ionic-domain distance increased, with a subsequent increase in lamellar ordering and long-range continuity. Further enhancement in morphological order was achieved by simply utilizing a selective solvent, dimethylacetamide, which is good and marginal for the sulfonated and unsulfonated blocks, respectively, rather than a neutral solvent, N-metyl-2-pyrrolidone. These morphological enhancements led to higher proton conductivity and water uptake. Drying temperature and/or solvent removal rate were observed to have considerable effects on water uptake and swelling behavior, being coupled with solvent selectivity. Also, the multiblock copolymer consisting of longer blocks was found to be more sensitive to the variation of the processing conditions such as solvent type and film drying temperature. [Copyright &y& Elsevier]

Abstract: H+-form Nafion 212 films were chemically degraded via Fenton''s reagent and characteristic polymer chain motions were analyzed using broadband dielectric spectroscopy. The β-relaxation peak maximum frequency (f max) shifts to higher temperatures upon degradation, reflecting slower chain motions. Perhaps this is due to an upward shift in average molecular weight caused by low molecular weight fragments being leached out of the membrane during the degradation experiment. Permittivity data for degraded and undegraded materials were fitted to the Havriliak–Negami equation. The quantities extracted from these fits were the relaxation time (τ) and parameters that reflect the breadth and asymmetry of the distribution of τ. These parameters were also used in the Vogel–Fulcher–Tammann–Hesse (VFTH) equation which was well-fitted to relaxation time versus temperature data. The increase in the Vogel temperature with degradation reflects more restricted chains. The distribution of relaxation time curve shifts to longer times, broadens, and is transformed from being bi- to tri-modal which reflects an increase in microstructural heterogeneity after degradation. It is concluded that dielectric spectroscopy can be a powerful tool in assessing the chemical degradation of Nafion membranes in the fuel cell environment. [Copyright &y& Elsevier]

Blends of poly(ethylene terephthalate) (PET) and poly(m -xylylene adipamide) (MXD6) were successfully compatibilized by using a phosphonated PET ionomer in the Na+ form (Na+-PPET) as a compatibilizer. The compatibilized 90:10 (by weight) polyester/polyamide blends containing various amounts of the phosphonated polyester were prepared by melt mixing in a twin-screw extruder. Scanning electron microscopy (SEM) revealed that the extruded blends contained spherical MXD6 domains dispersed in the PET matrix. The phase-separated MXD6 domain size decreased with increasing ionic monomer concentration, and the efficient compatibilization was attributed to specific interactions between the ionic phosphonate groups on the Na+-PPET ionomer and the amide linkages of MXD6. Thermal analysis suggested that the small MXD6 domains nucleated the crystallization of PET upon cooling as indicated by a shift of crystallization temperature of PET to higher temperatures. Furthermore, the specific interactions appeared to inhibit crystallization of MXD6. Biaxial orientation of melt processed films of the blends with a draw ratio of 3 × 3 transformed the spherical MXD6 domains into high aspect ratio platelets that were oriented in the plane of the film. Compared to the uncompatibilized base blends, optical property characterization on the oriented films revealed a decreased haziness by 56% and an improved transparency by 35% with 0.22 mol% of phosphonated ionic monomers incorporated in the polyester component. Moreover, a 33% decrease in oxygen permeability was found for the oriented Na+-PPET/PET/MXD6 blend composition containing 0.11 mol% of phosphonated monomers. Image 1 • Compatibilization of PET and MXD6 polyamide blends by using a new phosphonated PET ionomer (PPET). • Decreased MXD6 domain size with increasing ionic monomer concentration. • Decreased haze, increased transmittance, and improved oxygen barrier properties for biaxially oriented films. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) of aerogels increases the achievable geometric complexity, and affords fabrication of hierarchically porous structures. In this work, a custom heated material extrusion (MEX) device prints aerogels of poly(phenylene sulfide) (PPS), an engineering thermoplastic, via in situ thermally induced phase separation (TIPS). First, pre-prepared solid gel inks are dissolved at high temperatures in the heated extruder barrel to form a homogeneous polymer solution. Solutions are then extruded onto a room-temperature substrate, where printed roads maintain their bead shape and rapidly solidify via TIPS, thus enabling layer-wise MEX AM. Printed gels are converted to aerogels via postprocessing solvent exchange and freeze-drying. This work explores the effect of ink composition on printed aerogel morphology and thermomechanical properties. Scanning electron microscopy micrographs reveal complex hierarchical microstructures that are compositionally dependent. Printed aerogels demonstrate tailorable porosities (50.0-74.8%) and densities (0.345-0.684 g cm -3 ), which align well with cast aerogel analogs. Differential scanning calorimetry thermograms indicate printed aerogels are highly crystalline (≈43%), suggesting that printing does not inhibit the solidification process occurring during TIPS (polymer crystallization). Uniaxial compression testing reveals that compositionally dependent microstructure governs aerogel mechanical behavior, with compressive moduli ranging from 33.0 to 106.5 MPa., (© 2023 The Authors. Advanced Materials published by Wiley‐VCH GmbH.)

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 χ 12 = 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/cm 3 , porosities between 80 and 93%, and surface areas between 200 and 225 m 2 /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.

Mn dissolution has been a long-standing, ubiquitous issue that negatively impacts the performance of Mn-based battery materials. Mn dissolution involves complex chemical and structural transformations at the electrode-electrolyte interface. The continuously evolving electrode-electrolyte interface has posed great challenges for characterizing the dynamic interfacial process and quantitatively establishing the correlation with battery performance. In this study, we visualize and quantify the temporally and spatially resolved Mn dissolution/redeposition (D/R) dynamics of electrochemically operating Mn-containing cathodes. The particle-level and electrode-level analyses reveal that the D/R dynamics is associated with distinct interfacial degradation mechanisms at different states of charge. Our results statistically differentiate the contributions of surface reconstruction and Jahn-Teller distortion to the Mn dissolution at different operating voltages. Introducing sulfonated polymers (Nafion) into composite electrodes can modulate the D/R dynamics by trapping the dissolved Mn species and rapidly establishing local Mn D/R equilibrium. This work represents an inaugural effort to pinpoint the chemical and structural transformations responsible for Mn dissolution via an operando synchrotron study and develops an effective method to regulate Mn interfacial dynamics for improving battery performance., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)

Quantitative analysis of particle size and size distribution is crucial in establishing structure-property relationships of composite materials. An emerging soft composite architecture involves dispersing droplets of liquid metal throughout an elastomer, enabling synergistic properties of metals and soft polymers. The structure of these materials is typically characterized through real-space microscopy and image analysis; however, these techniques rely on magnified images that may not represent the global-averaged size and distribution of the droplets. In this study, we utilize ultra-small angle X-ray scattering (USAXS) as a reciprocal-space characterization technique that yields global-averaged dimensions of eutectic gallium indium (EGaIn) alloy soft composites. The Unified fit and Monte Carlo scattering methods are applied to determine the particle size and size distributions of the liquid metal droplets in the composites and are shown to be in excellent agreement with results from real-space image analysis. Additionally, all methods indicate that the droplets are getting larger as they are introduced into composites, suggesting that the droplets are agglomerating or possibly coalescing during dispersion. This work demonstrates the viability of X-ray scattering to elucidate structural information about liquid metal droplets for material development for applications in soft robotics, soft electronics, and multifunctional materials.

This manuscript describes the versatility of highly directional, noncovalent interactions, i.e., quadruple hydrogen bonding (QHB), to afford novel polyurea segmented supramolecular polymers for melt extrusion three-dimensional (3D) printing processes. The molecular design of the polyurea elastomers features (1) flexible polyether segments and relatively weak urea hydrogen-bonding sites in the soft segments to provide elasticity and toughness, and (2) strong ureido-cytosine (UCyt) QHB in the hard segments to impart enhanced mechanical integrity. The resulting polyureas were readily compression-molded into mechanically-robust, transparent, and creasable films. Optimization of polyurea composition offered a rare combination of high tensile strength (95 MPa), tensile elongation (788% strain), and toughness (94 MJ/m 3 ), which are superior to a commercially available Ninjaflex elastomer. The incorporation of QHB facilitated melt processability, where hydrogen bonding dissociation provided low viscosities at printing temperatures. During cooling, directional self-assembly of UCyt QHB facilitated the solidification process and contributed to part fidelity with the formation of a robust physical network. The printed objects displayed high layer fidelity, smooth surfaces, minimal warpage, and complex geometries. The presence of highly directional QHB effectively diminished mechanical anisotropy, and the printed samples exhibited comparable Young's moduli along ( x - y direction, 0°) and perpendicular to ( z -direction, 90°) the layer direction. Remarkably, the printed samples exhibited ultimate tensile strains approaching 500% in the z -direction prior to failure, which was indicative of improved interlayer adhesion. Thus, this design paradigm, which is demonstrated for novel polyurea copolymers, suggests the potential of supramolecular polymers with enhanced mechanical performance, melt processability, recyclability, and improved interlayer adhesion for melt extrusion additive manufacturing processes.

Preparation of polysaccharide-based block copolymers with linear architectures is an important goal, opening up clear application potential and requiring significant advances in polysaccharide regio- and chemoselectivity. Herein we report a simple approach to prepare dextran-based block copolymers. Reaction with N -bromosuccinimide (NBS)/triphenyl phosphine (PPh 3 ) regioselectively brominates the sole primary alcohol of linear, unbranched dextran at C-6 of the nonreducing end monosaccharide. The resulting dextran, monofunctionalized with a terminal C-6 bromide, was coupled with various amine terminated polymers to prepare block copolymers, including dextran- b -poly(ethylene glycol), dextran- b -polystyrene, and dextran- b -poly( N -isopropylacrylamide). These renewable-based block copolymers, prepared in two selective, high-yielding steps from native linear dextran, exhibit various interesting properties. Dextran- b -poly( N -isopropylacrylamide) undergoes thermally induced micellization as revealed by dynamic light scattering (DLS), forming micelles upon exceeding 33 °C. We also observed microphase separation in dextran- b -polystyrene by using small-angle X-ray scattering (SAXS). Overall, this methodology provides a new, highly chemo- and regioselective, versatile route to diverse dextran-based block copolymers with useful properties, enabling drug delivery, compatibilization, and other applications.

The phase diagram for the thermoreversible gelation of poly(ether ether ketone) (PEEK) in 4-chlorophenol (4CP) was constructed over broad temperature and concentration ranges, revealing that PEEK is capable of dissolving and forming gels in both 4CP and dichloroacetic acid (DCA) up to a concentration of 25 wt %. Highly porous aerogels of PEEK were prepared through simple solvent exchange followed by one of two drying methods of solvent removal from the wet gel: freeze-drying or supercritical CO 2 fluid extraction (SC-drying). The field-emission scanning electron microscopy analysis showed that gelation of PEEK in 4CP, followed by SC-drying, produced aerogels with well-defined lamellar aggregates as compared to less ordered aggregates formed from DCA. Mechanical properties (in compression) were shown to improve with increasing density, resulting in equivalent compressive moduli at comparable density, regardless of the preparation method (gelation solvent selection, concentration variation, or drying method). Nitrogen adsorption-desorption isotherms indicate that PEEK aerogels are comprised of mesopores (2-50 nm diameter pores) formed from stacked crystalline lamella. PEEK aerogels prepared using SC-drying exhibit higher Brunauer-Emmett-Teller surface areas than freeze-dried aerogels of comparable density. The ultra-small-angle X-ray scattering/small-angle X-ray scattering (SAXS)/wide-angle X-ray scattering analysis revealed a hierarchical morphology of the PEEK aerogels with structural features from PEEK crystallites to agglomerates of stacked lamella that spanned a wide range of length scales. SANS contrast-matching confirmed that the morphological origin of the principle scattering feature in PEEK aerogels is stacked crystalline lamella. Nitrogen sorption measurements of porosity and the specific surface area of the PEEK aerogels were correlated with the SAXS analysis to reveal a remarkably high surface area attributed to the platelet-like, lamellar morphology. Contact angle and contact angle hysteresis (CAH) revealed that low-density PEEK aerogels (ρ < 0.15 g/cm 3 ) have water contact angles above the superhydrophobicity cutoff angle (>150°) and a very low CAH near 1°.

Objective: The Joint Committee on Infant Hearing recommends that all newborns undergo hearing screening during their hospital birth admission or before one month of age. Also, infants with certain risk factors should receive audiologic monitoring every six months until three years of age. Initial treatment of sensorineural hearing loss involves the use of properly fitted binaural hearing aids with cochlear implantation indicated for use in children ages twelve months and older that have derived limited benefit from amplification. Cochlear implantation before two years of age is associated with improved language acquisition. Pediatric primary care physicians are crucial to the diagnosis and treatment of congenital hearing loss. This study provides a baseline assessment of Mississippi pediatric primary care physicians' understanding of the risk factors, diagnosis, treatment options, and role of cochlear implantation with regard to congenital hearing loss., Methods: A single page questionnaire consisting of sixteen questions about newborn hearing loss and cochlear implantation was mailed to all active members of the Mississippi Academy of Family Physicians and the Mississippi Chapter of the American Academy of Pediatrics., Results: Of the 501 surveys mailed out, 160 surveys were returned completed for a resultant 32% response rate. Out of the 160 physicians returning the questionnaire, 50 were general pediatricians, 89 were family practitioners, and 21 were physicians who did not practice primary care medicine for pediatric patients. The majority of questions were answered correctly by all groups. In most instances, there was a significant statistical difference with the pediatrician group having more correct responses as compared to the family practitioner group., Conclusions: The data presented demonstrate that primary care providers for children within the state of Mississippi are generally knowledgeable about the diagnosis and treatment of congenital hearing loss. Aspects of newborn hearing loss diagnosis and treatment to emphasize in future education efforts include: understanding the necessity of objective screening measures for the diagnosis of hearing loss, the need for hearing aid intervention by six months of age, and the role of early cochlear implantation in the mainstreaming of prelinguistically deaf children.

The chloroplast genes of dinoflagellates are distributed among small, circular dsDNA molecules termed minicircles. In this paper, we describe the structure of the non-coding region of the psbA minicircle from Symbiodinium: DNA sequence was obtained from five Symbiodinium strains obtained from four different coral host species (Goniopora tenuidens, Heliofungia actiniformis, Leptastrea purpurea and Pocillopora damicornis), which had previously been determined to be closely related using LSU rDNA region D1/D2 sequence analysis. Eight distinct sequence blocks, consisting of four conserved cores interspersed with two metastable regions and flanked by two variable regions, occurred at similar positions in all strains. Inverted repeats (IRs) occurred in tandem or "twin" formation within two of the four cores. The metastable regions also consisted of twin IRs and had modular behaviour, being either fully present or completely absent in the different strains. These twin IRs are similar in sequence to double-hairpin elements (DHEs) found in the mitochondrial genomes of some fungi, and may be mobile elements or may serve a functional role in recombination or replication. Within the central unit (consisting of the cores plus the metastable regions), all IRs contained perfect sequence inverses, implying they are highly evolved. IRs were also present outside the central unit but these were imperfect and possessed by individual strains only. A central adenine-rich sequence most closely resembled one in the centre of the non-coding part of Amphidinium operculatum minicircles, and is a potential origin of replication. Sequence polymorphism was extremely high in the variable regions, suggesting that these regions may be useful for distinguishing strains that cannot be differentiated using molecular markers currently available for Symbiodinium.