Lamellar Stacks Research Articles

Structure, performance and deposition control of the graphitic carbon protective layer in blast furnace hearth

Hundreds of operational blast furnaces annually are forced to be maintained using traditional methods due to hearth safety, significantly increasing carbonaceous fuel consumption and maintenance costs. Our team has pioneered a novel hearth maintenance approach, whose core lies in promoting the formation of a graphitic carbon protective layer. The key to forming this protective layer and optimizing its structure and performance lies in regulating the precipitation and growth behavior of graphite in blast furnace molten iron. This work first clarified the phase composition, morphology, crystal structure, growth direction, and high-temperature performance of the graphitic carbon protective layer by multiple characterization methods. The contents of C, Si, S, and Ti in the protective layer were much higher than those in molten iron, and the C content was up to 81.24 wt.%. Graphite exhibited macroscopically large-size flake morphology and microscopically lamellar stacking structure, and its preferred growth direction was [21-30]. The thermal conductivity of the protective layer decreased with increasing temperature. The CSLM in-situ experiments were conducted to reveal the effect of the molten iron elements on the precipitation and growth behavior of graphite. The elements that promote the graphite precipitation were Si, Ti, and C in order, while S inhibited it. The S, C, and Si promoted the lateral growth of graphite along the a-axis, and S was the strongest promoter. The effect of Ti on graphite growth was negligible. The control approach for promoting the deposition of flake graphite was proposed in terms of both temperature and molten iron elements.

Unraveling the changes of physical properties and nanostructures of rice starch incorporated with pregelatinized rice starch paste during gelatinization

In this study, we aimed to determine the influence of pregelatinized rice starch paste (PRSP) on the gelatinization of native rice starch, including its rheology and nanostructure. Gelatinization of PRSP-incorporated rice starch in excess water while heating at 5 °C/min was analyzed via rheometry, differential scanning calorimetry (DSC) and synchrotron small angle X-ray scattering (SAXS). Rheometry revealed that the addition of PRSP resulted in a more stable rice starch–water system at sub-gelatinization temperatures. A decrease from around 3000 Pa to lower than 1000 Pa in G′ was observed in the samples with PRSP after heating over 80 °C compared to that of the native starch. The sol-gel transition point of the starch–water system was altered by PRSP. DSC results showed no significant differences between the PRSP-incorporated and native starch. SAXS analysis revealed that the scattering invariant up to the gelatinization onset temperature was increased by the addition of PRSP due to the large volume fraction of the lamellar stacks. Correlation function-based structural parameters of the samples with PRSP changed earlier than those of native starch during heating due to the annealing effect. Moreover, the melting temperature of lamella of native starch was around 70 °C while those of the sample with PRSP were around 65 °C. Analysis of the radius of gyration (Rg) of the micellar structure after complete gelatinization indicated that Rg of native starch sample increased from 3.9 to 6.2 nm while that of the sample with 20% PRSP remained unchanged (≈ 4.3 nm). Overall, our results suggest that PRSP inhibits the swelling of rice starch during gelatinization and changes its rheological properties.

Oxygen vacancies-promoted oxidative esterification of ethylene glycol to methyl glycolate over Au/ZnO catalyst

Au/ZnO-x with different morphologies were prepared by controlling the amount of (NH4)2CO3 (x) using deposition precipitation method and applied for the one-step oxidative esterification of methanol and ethylene glycol (EG) to methyl glycolate (MG). The catalytic performance of Au/ZnO-x firstly increases and then decreases with the increase of the amount of (NH4)2CO3, and the maximum is achieved in Au/ZnO-4, with EG conversion of 89.6 % and 96.4 % selectivity to MG, significantly higher than the reported Au-based catalysts. The superior catalytic behavior is mainly derived from the most oxygen vacancy concentration (Vo+) accompanied with the highest I100/I101 ratio at moderate (NH4)2CO3 dosage, promoting the adsorption and dissociation of O2 molecular. Specifically, different preferential growth ratio between the (100) and (101) crystal plane accounts for Au/ZnO-2, Au/ZnO-4, and Au/ZnO-6 with lamellar stacking morphology, orderly layer structure, and randomly stacked layers, respectively. Significantly, it was found that there was a linear positive correlation between the Vo+ and the EG conversion. Innovatively, the oxygen vacancy played the predominant role in Au/ZnO-x for the catalyzed oxidative esterification of EG, which provided a new idea for the design of efficient catalysts for the reaction.

Design Principles for Enhancing Both Carrier Mobility and Stretchability in Polymer Semiconductors via Lewis Acid Doping

AbstractWith the rise of skin‐like electronics, devices are increasingly coming into close contact with the human body, creating a demand for polymer semiconductors (PSCs) that combine stretchability with reliable electrical performance. However, balancing mechanical robustness with high carrier mobility remains a challenge. To address this, tris(pentafluorophenyl)borane (BCF) for Lewis acid doping is proposed to improve charge mobility while enhancing stretchability by increasing structural disorder. Through systematic investigation, several key structural principles have been identified to maximize the effectiveness of BCF doping in stretchable PSCs. Notably, increasing the lamellar stacking distance and reducing crystallinity facilitate the incorporation of BCF into the alkyl side‐chain regions, thereby enhancing both mobility and stretchability. Conversely, stronger Lewis base groups in the main chain negatively impact these improvements. These results demonstrate that with a small addition of BCF, a two‐fold increase in carrier mobility is achieved while simultaneously enhancing the crack onset strain to 100%. Furthermore, doped PSCs exhibit stable mobility retention under repeated 30% strains over 1000 cycles. This method of decoupling carrier mobility from mechanical properties opens up new avenues in the search for high‐mobility stretchable PSCs.

Case Series of Thermal Cautery Artifact in Urine Cytology: An Uncommon Finding but a Potential Pitfall.

Therapeutic modalities used in bladder lesions/neoplasms (electrocautery, fulguration, and laser) could produce morphologic alterations leading to diagnostic challenges. While often seen on histology, they can present in urine cytology as atypia or even raise the concern for malignancy. Herein, we present clinicopathologic findings of four patients with cautery artifact in urine cytology. The authors' lists and a computerized search of urine cytology with features of thermal cautery artifact were collated. Slides and clinicopathologic variables (prior specimens, concurrent and follow-up surgical specimens, age, sex, manner of urine collection, cystoscopy, and treatment procedure during cystoscopy) were reviewed. Four cases were identified. Procedures performed during cystoscopy included laser therapy (n = 2), postbiopsy cauterization (n = 1), and fulguration (n = 1). All cases showed spindled cells with delicate bipolar cytoplasm, "cigar-shaped" nuclei, smooth to slightly irregular nuclear membranes, and arranged singly and loosely cohesive to lamellar stacks. Few atypical well-preserved, undistorted cells were identified in 2/4. The concurrent biopsies showed superficial cellular fragments with thermal artifact (n = 1) and rare atypical cells (n = 2). Follow-up biopsies in two cases had high-grade urothelial carcinoma both of which were diagnosed as atypical urothelial cells on cytology. Thermal cautery artifact in urine cytology is rare and can be seen following laser, electrocautery, and fulguration. The spindling artifact can render some degree of difficulty in assessing for the presence of urothelial atypia both in cytology and biopsy. Familiarity with these cytologic features, knowledge of the treatment procedure, attention to the cytologic findings of well-preserved cells and repeat sampling in cases with atypical urothelial cells in patients with history of malignancy is essential.

All-in-One Polymer Gel Electrolyte towards High-Efficiency and Stable Fiber Zinc-Air Battery.

Fiber zinc-air batteries are explored as promising power systems for wearable and portable electronic devices due to their intrinsic safety and the use of ambient oxygen as cathode material. However, challenges such as limited zinc anode reversibility and sluggish cathode reaction kinetics result in poor cycling stability and low energy efficiency. To address these challenges, we design a polydopamine-based all-in-one gel electrolyte (PAGE) that simultaneously regulates the reversibility of zinc anodes and the kinetics of air cathodes through polydopamine interfacial and redox chemistry, respectively. The intrinsic catechol and carboxylate groups in PAGE regulate the transport and solvation structure of Zn2+, facilitating dendrite-free zinc deposition with a lamellar stacking morphology. Additionally, the oxidation of redox-active catechol groups in PAGE replaces the sluggish oxygen evolution reaction on the air cathode and reduces the energy barrier for charging, enabling fiber zinc-air batteries to achieve a significantly improved energy efficiency of 95 % and a longer lifespan of 40 hours. Further integration into self-powered electronic textiles underscores its potential for next-generation wearable systems.

All‐in‐One Polymer Gel Electrolyte towards High‐Efficiency and Stable Fiber Zinc‐Air Battery

Fiber zinc‐air batteries are explored as promising power systems for wearable and portable electronic devices due to their intrinsic safety and the use of ambient oxygen as cathode material. However, challenges such as limited zinc anode reversibility and sluggish cathode reaction kinetics result in poor cycling stability and low energy efficiency. To address these challenges, we design a polydopamine‐based all‐in‐one gel electrolyte (PAGE) that simultaneously regulates the reversibility of zinc anodes and the kinetics of air cathodes through polydopamine interfacial and redox chemistry, respectively. The intrinsic catechol and carboxylate groups in PAGE regulate the transport and solvation structure of Zn2+, facilitating dendrite‐free zinc deposition with a lamellar stacking morphology. Additionally, the oxidation of redox‐active catechol groups in PAGE replaces the sluggish oxygen evolution reaction on the air cathode and reduces the energy barrier for charging, enabling fiber zinc‐air batteries to achieve a significantly improved energy efficiency of 95% and a longer lifespan of 40 hours. Further integration into self‐powered electronic textiles underscores its potential for next‐generation wearable systems.

Effective improvement of lithium-ion battery anode performance of Ti3C2 by alkali metal ion treatment strategy

MXene has emerged as a promising electrochemical energy storage material due to modifiable layered structure and good electrical conductivity. However, its lamellar stacking has severely limited the electrochemical performance during charging and discharging. Herein, the Li-treated Ti3C2 and Na-treated Ti3C2 nanocomposites are prepared by hydrothermal treatment. Li-treated Ti3C2 exhibits the largest discharge specific capacity, with an initial capacity of 551.5 mA h/g at a rate of 0.1 A/g, which is 81.3 mA h/g higher than Na-treated Ti3C2. After 200 cycles, the Li-Ti3C2 possesses a final capacity of 321.1 mA h/g, better than Na-Ti3C2 (151.7 mA h/g) and Ti3C2 (119.3 mA h/g). The Li-Ti3C2 shows superior cycling performance at a high rate of 2 A/g and a capacity retention rate of 84 % after 1000 cycles. During hydrothermal treatment, the in situ generated TiO2 plays a crucial role in the targeted introduction of metal ions. Density functional theory (DFT) calculations verify that LiTiO2 phase in Li-treated Ti3C2 possesses low band gap and lowest Li migration barrier. The synergy of these factors leads to the improved electrochemical performance of Li-treated Ti3C2. This work provides novel design strategies for developing MXene materials as high performance lithium-ion batteries.

Chain-Folded Lamellar Stacking Structure of the Crystalline Fraction of Bombyx mori Silk Fibroin with Silk II Form Studied by 2D 13C-13C Homonuclear Correlation NMR Spectroscopy.

The structure of Bombyx mori silk fibroin (SF) is a subject of significant interest due to its remarkable physical properties; however, its atomic-level structure is still not conclusive. We previously proposed a lamellar stacking structure for the crystalline fraction (Cp) with β-turns occurring every eighth amino acid. In this study, we took the following steps: At first, a model of the chain-folded lamellar stacking structure in antipolar and antiparallel β-sheet layers was constructed. Then, dipolar-assisted rotational resonance solid-state NMR spectra were observed to determine the effective internuclear distance (rj,keff) for the uniformly 13C-labeled Cp fraction sample. By comparing the experimentally obtained rj,keff (obs) values with the calculated rj,keff (calc) values from our structural model, a fairly good correlation between the observed and calculated values of the internuclear distances was obtained with a standard deviation of 0.37 Å. This supports the existence of the chain-folded lamellar stacking structure in the SF fiber. These findings contribute to our understanding of the atomic-level structure of SF and its exceptional properties.

Oligo-cyclic loading-induced evolution of stress distribution and apparent amorphous modulus in lamellar stacks of high-density polyethylene

Assessing the resistance of high-density polyethylene (HDPE) against earthquake-like loads involves understanding the changes in structure and properties induced by oligo-cyclic loading at various length scales. To study the evolution of stress distribution and intrinsic properties within lamellar stacks from pristine to oligo-cyclic loading pre-conditioned materials, simultaneous in-situ SAXS/WAXS measurements were performed. During the elastic deformation of each pristine and preconditioned sample, crystal strain was tracked using the in-situ WAXS technique. Based on the established elastic tensor of the crystalline structure in polyethylene, we calculated the microscopic stress values within crystalline lamellae. In the pristine sample, lamellar stacks exhibit closely series-like coupling in the equatorial region and parallel-like coupling in the polar region of the spherulite. In the pre-conditioned sample, stress is primarily concentrated in the intra-fibrillar region, where the crystalline and amorphous phases are series-coupled, and strong strain concentration occurs in the inter-fibrillar region. By combining the local strain in the amorphous layer within the lamellar stacks in the equatorial region of the spherulite and the intra-fibrillar region with series-coupled lamellar stacks, measured by in-situ SAXS tests, the apparent amorphous modulus at the lamellar stack scale can be determined. This modulus changes from 71 to 106 MPa in the equatorial region of pristine spherulites to a notable 2000–7000 MPa in the intra-fibrillar region under the influence of oligo-cyclic pre-loading. Importantly, this apparent modulus is affected by both crystallization conditions and molecular structure, with molecular parameters exerting the primary influence.

Based on size-exclusion effect of selective removal of organic pollutants in complex water quality by low temperature plasma: Degradation behavior and selective mechanism analysis

The presence of natural organic matters (NOMs) will have a negative effect on the removal of small molecule organic contaminants in complex water quality, therefore, it’s very important to design a catalyst with size-exclusion function to achieve the selective removal of targeted pollutant. Herein, a novel ZIF-L catalyst precursor with lamellar stack structure is designed, and iron as heteroatom is doped in ZIF-L gaps named ZIF-L@Fe. After pyrolysis, Fe ions are transformed into Fe nanoparticles, and act as the active sites of catalyst. In order to verify the selective removal ability of resulted NSC@Fe in dielectric barrier discharge (DBD), tetracycline hydrochloride (TTCH) and humic acid (HA) is selected as the target pollutant and coexistence macromolecular interferent, respectively. In the presence of HA (50 mg/L), the degradation rate of TTCH in the system is not significantly affected (with HA, k = 0.037 min−1; without HA, k 0.036 min−1), which is mainly due to the layered material stacking characteristics (size-exclusion). The degradation mechanism and pathway are further confirmed by radical quenching experiments and liquid chromatography−mass spectrograph (LC−MS), respectively. This study is believed to shed new light on how to rationally design catalyst with selective removal of organic pollutants in complex water quality for water remediation.

Photocatalytic persulfate activation by silica microsphere-supported g-C3N4 for efficient carbamazepine degradation

A silica-loaded g-C3N4 composite photocatalyst (M-SiO2/g-C3N4) was prepared by grinding amorphous SiO2 microspheres (M − SiO2) with melamine and calcining the resulting grinding products. This composite was used for photocatalytic persulfate (PMS) activation to degrade carbamazepine (CBZ). The results showed that the degradation efficiencies of CBZ by M-SiO2/g-C3N4-2.5 (39.16 % of g-C3N4)-activated PMS were 78.92 % and 100 % after simulated sunlight irradiation for 60 and 120 min, respectively. These values were significantly greater than those of the system with pure g-C3N4 (29.15 % and 42.4 %). In particular, the degradation efficiency of CBZ with M-SiO2/g-C3N4-2.5 decreased by only 9.47 % after 4 cycles of recycling. In the catalytic process, h+, SO4•− and O2•− were the main reactive species contributing to CBZ degradation. Compared with g-C3N4, loading g-C3N4 on the surface of M − SiO2 resulted in a decrease in g-C3N4 lamellar stacking, which increased the number of active surface sites and improved the separation and migration of photogenerated carriers, improving the degradation performance.

Crystal structural evolution and cavitation in biodegradable polyglycolide: An in-situ WAXD/SAXS study during hot-stretching

The structural evolution of high-crystallinity polyglycolide (PGA) during hot-stretching from 50 °C to 150 °C was investigated using synchrotron in-situ WAXD/SAXS techniques. The structural evolution during stretching at different temperatures can be divided into three stages. The stage preceding the yield point, the lamellar crystals undergo extensive slip due to shear forces. The crystallite size decreases by 43.9 % during stretching at 50 °C, while it only decreases by 23.8 % at 150 °C. In this stage, cavities with their long axes vertical to the stretching direction form between the lamellar stacks parallel to the stretching direction. Higher stretching temperatures are less favorable for the formation of these cavities. Stage from yield point to onset of strain hardening, some of the small crystals formed in the previous stage accumulate in the oblique direction. After reaching the critical strain, they reorient towards the stretching direction. This reorientation causes fragmentation and recrystallization, promoting the further development of cavities. Both the cavities and the recrystallized crystals align along the stretching direction. In the strain-hardening stage, new crystal formation occurs under stress, and higher temperatures favor the formation of highly oriented crystals. As a result, the crystallinity and crystal orientation of PGA at the end of stretching are positively correlated with the stretching temperature.

Effect of interface type on deformation mechanisms of γ-TiAl alloy under different temperatures and strain rates by molecular dynamics simulation

Crystalline interface plays a significant role in strengthening lamellar γ-TiAl alloys through reconciling the strength and ductility. Herein, the effects of temperature and strain rate on the tensile deformation of three lamellar γ-TiAl interface models are investigated by molecular dynamics simulations. The three interfaces, pseudo twin (PT), rotational boundary (RB), and true twin (TT), exhibit different tensile responses due to the different interface effects: TT interface only acts as a barrier of dislocation traversing to facilitate crack extension; PT interface acts as both dislocation barrier and emission source and has a stronger release of strain energy than TT interface, retarding the crack extension; RB interface can retard and resist crack extension due to the blunting and deflection of the crack tip and the best interface geometry compatibility. The defect evolution indicates that the elevated temperature suppresses dislocation propagation at low strain rate, while the high strain rate causes small lamellar stacking faults and slit-shaped holes along tensile direction at low temperature. In addition, the dual conditions of high strain rate and low temperature induce the phase transition from FCC to BCC and then BCC to HCP. These findings provide a specific insight to understand the atomistic mechanism of interface-mediated deformation.

Evolution of elliptical SAXS patterns in aligned systems.

Small-angle X-ray and neutron scattering (SAXS and SANS) patterns from certain semicrystalline polymers and liquid crystals contain discrete reflections from ordered assemblies and central diffuse scattering (CDS) from uncorrelated structures. Systems with imperfectly ordered lamellar structures aligned by stretching or by a magnetic field produce four distinct SAXS patterns: two-point 'banana', four-point pattern, four-point 'eyebrow' and four-point 'butterfly'. The peak intensities of the reflections lie not on a layer line, or the arc of a circle, but on an elliptical trajectory. Modeling shows that randomly placed lamellar stacks modified by chain slip and stack rotation or interlamellar shear can create these forms. On deformation, the isotropic CDS becomes an equatorial streak with an oval, diamond or two-bladed propeller shape, which can be analyzed by separation into isotropic and oriented components. The streak has elliptical intensity contours, a natural consequence of the imperfect alignment of the elongated scattering objects. Both equatorial streaks and two- and four-point reflections can be fitted in elliptical coordinates with relatively few parameters. Equatorial streaks can be analyzed to obtain the size and orientation of voids, fibrils or surfaces. Analyses of the lamellar reflection yield lamellar spacing, stack orientation (interlamellar shear) angle α and chain slip angle ϕ, as well as the size distribution of the lamellar stacks. Currently available computational tools allow these microstructural parameters to be rapidly refined.

Morphology, functional groups, and CO2 adsorption performance of Cu2(OH)PO4: Effects of synthesis conditions

Global warming, primarily driven by emissions of greenhouse gases, particularly carbon dioxide, has emerged as a widely acknowledged concern. Hence, the development of novel carbon capture materials with high capacity and low cost holds substantial practical significance. This study investigates the influence of aging time, pH, and copper salt on the synthesis of Cu2(OH)PO4 and its CO2 adsorption performance. Cu2(OH)PO4 adsorbents were synthesized under various aging time, pH, and copper salt conditions, and their morphology and surface functional groups were characterized. Experimental findings indicate that excessively prolonged or abbreviated aging times adversely affect the formation of distinct, discernible lamellar structures within the material. Different pH levels influence the stacking configuration of the lamellae, impacting both their thickness and size. Under acidic conditions, lamellae exhibit dispersed three-dimensional stacking; under neutral conditions, lamellae notably enlarge and demonstrate two-dimensional stacking; at pH 9, lamellae stack three-dimensionally and aggregate. Additionally, the CO2 adsorption performance of Cu2(OH)PO4 adsorbents synthesized with different copper salts varies. By examining the relationship between surface functional group content and CO2 adsorption capacity, we deduced the mechanism by which various synthesis conditions affect both surface functional groups and adsorption capacity. Cu2(OH)PO4 synthesized with a 24 h aging time, pH 7, and CuSO4 as the copper salt exhibits the highest CO2 adsorption capacity, achieving 1.006 mmol/g.

Coupling various in-situ methods to reveal the peculiar semi-crystalline morphology of melt-processed fluorinated copolymers

Poly(vinylidene fluoride-co-trifluoroethylene) (P(VDF-co-TrFE)) copolymer and poly(vinylidene fluoride-ter-trifluoroethylene-ter-chlorotrifluoroethylene) P(VDF-ter-TrFE-ter-CTFE) terpolymer thin films are usually produced by solvent-casting followed by annealing to enhance their electroactive properties in electronic devices. In this study, we investigate the effect of a different thermal treatment, namely crystallization from the melt, on the crystalline structure and morphology of P(VDF-ter-TrFE-ter-CTFE) terpolymers with varying CTFE content (ranging from 0 to 8.3 mol %) using a combination of different in-situ techniques. First, in-situ Wide-Angle X-Ray Scattering (WAXS) shows the different crystal-crystal transitions during cooling for all the samples. For the terpolymers, two sharp Bragg peaks ((110) and (200) family of planes) of the low temperature crystalline phase can be detected. Their sharpness reflects a high lateral extension of the crystalline domains. Moreover, coupled morphological studies by in-situ Small-Angle X-Ray Scattering (SAXS) and Atomic Force Microscopy (AFM) show that the crystallization starts with the formation of very extended semi-crystalline domains with a sub-micrometric thickness that contributes to the SAXS signal. For significant amounts of CTFE, crystallization is spread out, leading to the appearance of increasingly finer lamellar stacks during cooling, filling the spaces left unoccupied during crystallization at higher temperatures. This contrasts with the very rapid crystallization observed in the polymer with 0 mol % of CTFE. Finally, the Curie transition is clearly visible in the AFM mechanical images, providing an original method for detecting the structural transitions occurring in these polymers.

Structural Characteristics of Fibrillar Crystals in Uniaxially Stretched Isotactic Polypropylene Dominated by Temperature and Strain

AbstractThe spherulitic morphology of isotactic polypropylene can be transformed into the oriented fibrillar morphology through hot stretching processes with varying temperature (Ts) or altering strain (εt). The effects of Ts and εt on the structural characteristics of fibrillar crystals are comprehensively investigated with respect to crystal orientation, long periodic spacing, lamellar thickness (Lc), crystallinity (Xc), melting point, and chain relaxation behavior. Small‐angle X‐ray scattering patterns illustrate that the fibrillar crystals consist of alternated stacks of crystalline lamellae and amorphous layers. High Ts leads to a low orientation degree of lamellae, whereas large εt facilitates a high orientation level. The Xc and mean Lc are improved continuously with the increasing of Ts or εt, indicating a stretching‐enhanced crystallization behavior driven by the two factors. The endothermic profiles reveal that new chain‐folded lamellae with relatively thinner thickness form during the hot stretching process. The formation of thinner lamellae is dominated by the melting–recrystallization mechanism. This work would provide guidance for optimizing process conditions to manipulate the microstructure of hot‐stretched semicrystalline polymers.

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

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.

Strain Rate Dependence of Amorphous Phase Instability in Semicrystalline Polymers: Insights from the Scale of Lamellar Stacks

Strain Rate Dependence of Amorphous Phase Instability in Semicrystalline Polymers: Insights from the Scale of Lamellar Stacks