Marine energy harvesting technologies demand composite materials capable of withstanding harsh and variable marine environments. In this study we develop and evaluate a fully bio-based composite system by combining a bio-derived epoxy resin with flax fiber reinforcement for marine applications. The DGMeOHQ-based epoxy system was synthesized from bio-based feedstocks and cured with IPDA, a bio-based hardener, at 100-160 °C. The resulting thermoset exhibited a glass transition temperature (Tg) of ~120 °C and a room-temperature storage modulus of 2.1 GPa, indicating robust thermomechanical performance. Composite panels were manufactured using the DGMeOHQ-IPDA resin with flax fibers, and for benchmarking, with commercial glass fibers and a commercial epoxy (phenol-novolak) system. Mechanical performance was evaluated following ASTM standards, including tensile, flexural, and saline-submersion conditioning tests. While flax fiber composites exhibited lower maximum tensile and flexural loads than glass fiber laminates (≈6 kN vs. 18-21 kN in tension), they showed markedly different failure behavior under marine-relevant conditions. After saline conditioning, flax composites exhibited a nearly twofold increase in flexural extension (≈10-25 mm) and suppressed brittle fracture, indicating enhanced toughness and energy absorption. These findings suggest that bio-based flax fiber composites are well-suited for marine components where damage tolerance, large deformation, and energy dissipation are critical.

Herein, we describe the synthesis and characterization of an all-aromatic, liquid-crystalline polyelectrolyte prepared via stirred liquid-liquid interfacial polycondensation. The polyelectrolyte, poly(2,2 '-disulfonyl-4,4 ' benzidine terephthalamide) (PBDT), self-assembles into helical dimers that form high-aspect-ratio, rodlike structures in aqueous solution. These helical aggregates undergo isotropic-to-nematic (I-N) transitions at concentrations as low as 0.8 wt%, corresponding to Onsager effective rod lengths of approximately 560 nm. When PBDT is synthesized with an excess molar ratio of terephthaloyl chloride (TPC), the resulting carboxylic acidterminated PBDT (PBDT-TPC) exhibits liquid crystalline behavior at concentrations below 1.0 wt%, with effective rod lengths of similar to 500 nm. In contrast, synthesis with excess 4,4 '-diaminobiphenyl-2,2 '-disulfonic acid (BDSA) yields amine-terminated PBDT (PBDT-BDSA) with reduced effective rod-lengths ranging from 110 to 350 nm, depending on the amount of excess BDSA. Rheology experiments reveal that both PBDT and PBDT-TPC solutions undergo irreversible gelation at 7.0 wt%, suggesting end-to-end rod growth between PBDT assemblies via carboxylic acid and amide/sulfonate hydrogen bonding under shear. In comparison, PBDT-BDSA solutions exhibit more gradual shear thickening behavior, indicative of weaker hydrogen bonding interactions involving amide and excess amine end-groups. Thin film tensile testing shows that PBDT-BDSA films produced from syntheses with a large excess of BDSA display poor stress-strain behavior, consistent with the formation of low molecular weight polymers and weak end-group associations. Conversely, PBDT-TPC films prepared using an excess of TPC exhibit excellent stress-strain properties, reflecting the formation of effectively high molecular weight polymer chains and strong carboxylic acid and amide/sulfonate hydrogen bonding interactions.

A series of thermally stable, hyperbranched poly(aryletherketone)s (hbPAEKs), functionalized with 4-(phenyl-ethynyl)phenol (PEP) reactive end-groups, were synthesized and evaluated as potential membranes for high-temperature gas separation applications. Despite their all-aromatic nature, the hbPAEKs can easily be processed into thin films from cyclopentanone and thermally crosslinked to form glassy films with high glass transition temperatures (Tg). The effect of crosslinking on Tg and the excess free fractional volume (EFFV) were studied using in-situ spectroscopic ellipsometry. Crosslinking hbPAEKs results in a significant increase in both Tg (from 140 to 250 degrees C) and EFFV (from 5 to 9.5 %). High-pressure CO2 sorption experiments demonstrated that crosslinked hbPAEKs resist plasticization at CO2 pressures up to 50 bar. When evaluating the gas separation performance at 200 degrees C, a crosslinked hbPAEK membrane with 10 mol% PEP exhibited exceptional stability, maintaining constant H2 and N2 permeance and H2/N2 selectivity for 2 weeks. Our findings indicate that crosslinked hbPAEK membranes hold great promise for high temperature gas separation applications.

All-aromatic calamitic liquid crystals are an unconventional family of rigid linear mesogens that represents the closest embodiment of the idealised rod-like molecule central to liquid crystal theories. 2,6-biphenyl naphthalene (PPNPP), a prototypical all-aromatic nematogen, has recently been the focus of scientific interest for both fundamental and technological purposes. While it provides a valuable benchmark for classical theories of nematic order, its experimental study presents challenges given the high temperature of the nematic phase. Herein, molecular dynamics (MD) simulations are contrasted with X-ray diffraction (XRD) data to resolve the thermotropic phase behaviour of PPNPP and the main structural features of its liquid crystal order. The observed trend of the molecular conformation with temperature points to an unexpected and significant distortion of the molecular framework in the nematic phase, which demonstrates the substantial non-linearity of the PPNPP molecule. The simulated mesomorphic behaviour and related thermodynamic parameters are in close agreement with the experimental data. The different phases are described in terms of their molecular organisation, pair distribution function, as well as the orientational and positional order parameters. We compare the classical and extended Maier-Saupe nematic theories with the computationally (MD) and experimentally (XRD) determined orientational order parameters. The observed deviation from the theoretical models indicates substantial inadequacies of the classical theories to describe the nematic-isotropic phase transition for this class of compounds. We suggest that modifications of theory should include the effects of short-range positional order, i.e., cybotaxis.

The behavior of a synthetic self-assembled rodlike polyelectrolyte is investigated both in salt-free solutions and in the presence of monovalent salt. The inherent rigidity and rodlike nature of poly(2,2 '-disulfonyl-4,4 '-benzidine terephthalamide) (PBDT) in salt-free aqueous solutions results in a nematic liquid-crystalline transition at a 1.0 wt % concentration. Specific viscosity eta(sp) of PBDT scales with concentration (c) as eta(sp) similar to c(1.2) in semidilute salt-free solutions, which deviates from the behavior of most semidilute polyelectrolyte solutions that follow Fuoss law (eta(sp) similar to c(0.5)). Additionally, PBDT solutions containing 30 mM NaCl reveal a crossover concentration (c > c(x)) and show up to a greater than 20-fold increase in eta(sp) compared with salt-free PBDT solutions at the same concentration. Oscillatory rheology experiments display a rise in modulus at all frequencies for PBDT solutions containing 10 mM NaCl and above, suggesting an increase in rod-rod association strength. X-ray scattering studies in salt-free semidilute PBDT solutions reveal polyelectrolyte correlation length (xi) scaling as epsilon similar to c(-0.43 +/- 0.03), which is a weaker dependence than typical scaling (xi similar to c(-1/2)) due to the balance of electrostatic and associative intermolecular interactions. We propose that PBDT can serve as a synthetic model system for studying the solution behavior of associative rodlike polyelectrolytes.

This work explores the effects of rigid (0.1, 0.25, and 0.5 wt. %) and semi-flexible (0.5, 1.0, and 2.5 wt. %) all-aromatic polyelectrolyte reinforcements as rheological and morphological modifiers for preparing phosphate geopolymer glass–ceramic composites. Polymer-modified aluminosilicate–phosphate geopolymer resins were prepared by high-shear mixing of a metakaolin powder with 9M phosphoric acid and two all-aromatic, sulfonated polyamides. Polymer loadings between 0.5–2.5 wt. % exhibited gel-like behavior and an increase in the modulus of the geopolymer resin as a function of polymer concentration. The incorporation of a 0.5 wt. % rigid polymer resulted in a three-fold increase in viscosity relative to the control phosphate geopolymer resin. Hardening, dehydration, and crystallization of the geopolymer resins to glass-ceramics was achieved through mold casting, curing at 80 °C for 24 h, and a final heat treatment up to 260 °C. Scanning electron microscopy revealed a decrease in microstructure porosity in the range of 0.78 μm to 0.31 μm for geopolymer plaques containing loadings of 0.5 wt. % rigid polymer. Nano-porosity values of the composites were measured between 10–40 nm using nitrogen adsorption (Brunauer–Emmett–Teller method) and transmission electron microscopy. Nanoindentation studies revealed geopolymer composites with Young’s modulus values of 15–24 GPa and hardness values of 1–2 GPa, suggesting an increase in modulus and hardness with polymer incorporation. Additional structural and chemical analyses were performed via thermal gravimetric analysis, Fourier transform infrared radiation, X-ray diffraction, and energy dispersive spectroscopy. This work provides a fundamental understanding of the processing, microstructure, and mechanical behavior of water-soluble, high-performance polyelectrolyte-reinforced geopolymer composites.

The development of perovskite solar cells (PSCs) has ushered in a new era of solar technology, characterized by its exceptional efficiency and cost-effective production. However, the soft and fragile nature of perovskites makes module encapsulation challenging. Polyolefin elastomers (POEs) have been reported to be promising encapsulants for perovskite modules. However, little research exists on identifying criteria among different types of POEs as encapsulants. Here, two POEs with different morphologies were compared as encapsulants. The first POE crystallizes during encapsulation (crystal content ∼40%), and the resulting shrinkage or warpage leads to delamination, causing minimodule failure. In contrast, perovskite minimodules encapsulated with a mostly amorphous POE exhibited better reliability and reproducibility. The best perovskite minimodules passed the thermal cycling test for 240 cycles between −40 and 85 °C and the damp heat test for 1419 h, according to the IEC 61215 standard. This study highlights the importance of the morphology of encapsulants in achieving high-quality encapsulation. Published by the American Physical Society 2024

Herein, we describe the synthesis and properties of a liquid crystal all-aromatic polyamide with tunable sulfonated content that can be converted into its poly(benzoxazole-co-amide) analog using a simple thermal treatment step. The parent all-aromatic polyamide, poly(3,3 '-dihydroxybenzidine terephthalamide) (DHTA), is modified by incorporating a sulfonated comonomer, 2,5-diaminobenzenesulfonic acid (DABS) (i.e., 5, 10, 25, and 50 mol% DABS), to yield sulfonated, random copolyamides (DHTA-y-DABS). The ortho-positioning of the hydroxyl group relative to the amide bond allows DHTA-y-DABS to undergo a cyclodehydration reaction from 200 to 450 degrees C, forming a sulfonated poly(benzoxazole-co-amide) while preserving the sulfonate functionalities. Swelling experiments show that the DHTA-y-DABS-Na+ films exhibit water uptake values ranging from 9 to 41 wt%. PBO-yDABS-Na+ films swell between 4 and 15 wt% in water. Dry films exhibit excellent mechanical properties. Young's moduli are between 8 and 10 GPa, yield strength values range from 117 to 215 MPa and elongation at break values range from 3 to 10%.

We have explored the structure-property relationships of a series epoxy-methylolphenol based thermoset films. Ortho-, meta-, and para-isomers of methylolphenol, that is, ortho-methylolphenol, meta-methylolphenol and para-methylolphenol, respectively, were reacted with the diglycidyl ether of bisphenol A (DGEBA) in the presence of an acid catalyst (CYCAT (R) XK 406 N). Thermogravimetric analyses showed that irrespective of the methylolphenol structure used, all crosslinked films exhibit 5% weight loss at 343-360 degrees C under nitrogen. The glass transition temperature (T-g) decreases in the order of ortho- (T-g = 117 degrees C) > para- (T-g = 102 degrees C) > meta-methylolphenol (T-g = 82 degrees C) as measured by differential scanning calorimetry. Uniaxial tensile testing of thin films shows good stress-strain behavior, with ultimate tensile strength values of 75 MPa and 6% strain-at-break. Homo-crosslinking of methylolphenol moieties can occur under the reaction conditions used but in the presence of DGEBA, the methylolphenols prefer to undergo epoxy ring-opening reactions. This was confirmed by the uniform networks that were formed, that is, no block-formation was observed. The results of this study confirm that simple methylolphenol hardeners can be used to prepare crosslinked epoxy-based films with excellent thermomechanical properties.

Single-ion-conducting electrolytes enable easy processingand canblock Li dendritic growth, showing potential for use in solid-statebatteries. We report solid electrolytes that combine a rigid-rod polyanion,poly(2,2 & PRIME;-disulfonyl-4,4 & PRIME;-benzidine terephthalamide)(PBDT), with Na+ or Li+ counterions, and poly(ethyleneglycol) (PEG, M (n) = 400 g mol(-1)). PBDT-PEG membranes show Young's modulus from 90 to 2110MPa that increases with the PBDT content and is >4x higherforLi-based vs Na-based electrolytes. We attribute this dramaticallyhigher modulus in LiPBDT-PEG to poorer ion dissociation betweenLi(+) and PBDT sulfonate groups and stronger interactionsbetween LiPBDT and PEG. These membranes show an increase in ionicconductivity with increasing PEG concentration (0.1-7 & mu;Scm(-1) at 30 & DEG;C), reaching 0.13 mS cm(-1) at 120 & DEG;C. These materials use highly rigid and charged PBDTdouble helices to "solidify" low-molecular-weight PEGinto mechanically strong and highly single-ion-conductive solid polymerelectrolytes with high thermal stability. Their combination of highcation conductivity and high modulus exceeds those of competing single-ionconductors at 30 & DEG;C.

We'll report on two series all-aromatic main-chain reactive oligomers that can be crosslinked in either the nematic phase or in the isotropic phase. This series is unique in that both model systems have an identical backbone geometry, comprised of hydroquinone with or without a phenyl substituent and phenyl substituted terephthalic acid. Crosslinking the oligomers (M-n of 1-9 kg/mol) via maleimide end-groups in the nematic or isotropic phase yields networks with similar crosslink densities (M-c) and similar thermal properties. Crosslinked films exhibit high decomposition temperatures (>395 degrees C) and amorphous thermoset films exhibit T-g's in the 141-190 degrees C range whereas nematic thermoset films give T-g's that range from 143 to 176 degrees C, as measured by DMTA. However, the phase type appears to have a major effect on the stress-strain behavior of the films. All films prepared by crosslinking un-aligned nematic oligomers show poor stress-strain behavior (sigma = 20-63 MPa, epsilon = 0.5%-5.4%), whereas crosslinking the amorphous oligomers results in films with excellent stress-strain properties (sigma = 94-97 MPa, epsilon = 7.1%-13.3%). The superior toughness of the cured amorphous films can be attributed to the larger free volume induced by steric crowding of the phenyl substituents in the polymer repeat unit.

Two aromatic polyamides─poly(3,3'-dihydroxybenzidine terephthalamide) (DHTA) and poly(3,3'-dihydroxybenzidine isophthalamide) (DHIA)─are compared for their ability to remove salts from water. DHTA is linear and rigid whereas DHIA is nonlinear and semirigid. DHTA and DHIA were selected as they allow us to investigate the effect of polymer backbone geometry on salt exclusion in a non-crosslinked thin film membrane, independently of the backbone chemistry. Because of their differences in solution viscosity, spin coating parameters for DHTA and DHIA solutions were optimized separately to produce thin film composites (TFCs) with reproducible membrane properties. The resulting DHTA TFCs displayed salt rejections of 87.8% (NaCl), 97.0% (MgSO4), and 80.3% (CaCl2). In comparison, DHIA TFCs demonstrated poor salt rejections of 21.0% (NaCl), 29.3% (MgSO4), and 15.4% (CaCl2). Cross-sectional SEM images of DHTA and DHIA films reveal that DHTA has a stratified (layered) morphology whereas DHIA exhibits a dense, featureless morphology. Both DHTA and DHIA TFCs exhibit similar surface morphology, contact angle, surface charge, and water uptake. PEG rejection experiments indicate that the average pore size of DHTA TFCs is ∼2 nm while DHIA TFCs have an average pore size of ∼3 nm. Our findings illustrate that using a rigid, linear aromatic polyamide gives an active layer with a stratified morphology, uniplanar orientation, smaller pores, and higher salt rejection, whereas the nonlinear aromatic polyamide analogue results in an isotropic active layer with larger pores and lower salt rejection.

We report on the morphology and mechanical properties of nanocomposite films derived from aqueous, hybrid liquid crystalline mixtures of rodlike aggregates of a sulfonated, all-aromatic polyamide, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT), and graphene oxide (GO) platelets. An isothermal step at 200 °C facilitates in situ partial thermal reduction of GO to reduced GO (rGO) in nanocomposite films. X-ray scattering studies reveal that PBDT-rGO nanocomposites exhibit both higher in-plane alignment of PBDT (the order parameter increases from 0.79 to 0.9 at 1.8 vol % rGO) and alignment along the casting direction (from 0.1 to 0.6 at 1.8 vol % rGO). From dynamic mechanical thermal analysis, the interaction between PBDT and rGO causes the β-relaxation activation energy for PBDT to increase with rGO concentration. Modulus mapping of nanocomposites using atomic force microscopy demonstrates enhanced local stiffness, indicating reinforcement. From stress-strain analysis, the average Young's modulus increases from 16 to 37 GPa at 1.8 vol % rGO and the average tensile strength increases from 210 to 640 MPa. Despite polymer alignment along the casting direction, an average transverse tensile strength of 230 MPa is obtained.

A novel series membranes based on non-linear all-aromatic polyimides (PIs) was investigated with the aim to understand how the PI backbone geometry and local electrostatics govern gas transport and the ability to separate CO2/CH4 mixtures. Non-linear 3-ring aromatic diamines, with exocyclic bond angles varying between 120 and 134 degrees, enable the design of high Tg (>276 degrees C) PIs. A polar 1,3,4-oxadiazole diamine (ODD) (mu = 3D) monomer and a non-polar m-terphenyl diamine (TPD) reference monomer were synthesized and coupled with 3 dianhydrides, i.e. ODPA, ODDA, and 6FDA. In 6FDA-based membranes CO2 permeabilities (PCO2) are the highest of the series. The 6FDA-ODD membrane shows excellent membrane performance with high PCO2 values at all feed pressures. Up to 12 bar (6 bar CO2) none of the membranes reached their plasticization pressure. The non-linear backbone geometry promotes CO2 permeability, whereas the presence of an electrostatic dipole moment asso-ciated with the 1,3,4-oxadiazole heterocycle governs CO2/CH4 separation selectivity.

Polyelectrolytes are widely used in heavy metal removal, finding applications as coagulants and flocculants. We compare the heavy metal removal capability of a water-soluble sulfonated semirigid polyamide, poly(2,2'-disulfonyl-4,4'-benzidine isophthalamide) (PBDI), with that of a well-known random-coil polymer, poly(sodium 4-styrenesulfonate) (PSS). Using lead (Pb(II)) as a model contaminant, both polymers precipitate out from solution at ~500 mg/L Pb(II) in water. The ability to remove Pb(II) from water was quantified using adsorption isotherms and fitted with Langmuir and Freundlich adsorption models. The sorption of Pb(II) by PSS fit the Langmuir model with a high degree of correlation (0.976 R2), but the sorption of Pb(II) by PBDI could not be accurately predicted using the Langmuir or Freundlich model. The sorption of Pb(II) by PBDI and PSS was compared by normalizing sorption by the number of sulfonate groups of each polymer and the ion exchange capacity (IEC), found by titration. We find that PBDI removes a greater amount of Pb(II) per gram of sorbent compared to PSS, 410 mg/g vs 260 mg/g, respectively, which cannot be accounted for by differences in IEC or number of sulfonate groups. Our findings confirm that the positioning of the sulfonate groups and the rigidity of the polymer backbone play an important role in how Pb(II) coordinates to the polymer prior to precipitating out from solution.

In order to better understand the design rules of epoxy-phenol thermosets we will report on the chemistry and (thermo)mechanical properties of cured epoxy-phenol thermoset films. Ortho-, meta- and para-isomers of dihydroxybenzene (DHB) were reacted with the diglycidyl ether of bisphenol A (DGEBA) in the presence of an acid catalyst or triphenylphosphine (PPh3). The glass transition temperatures (T-g) of the cross-linked films decreases in the order of meta- (T-g = 115 degrees C) > ortho- (T-g = 102 degrees C) > para-DHB (T-g = 96 degrees C) as measured by differential scanning calorimetry. Uniaxial tensile testing of cross-linked films showed excellent stress-strain behavior. The average ultimate strength values ranged from 65 to 82 MPa and the average values of the strain-at-break ranged from 4.8% to 6.9% at 25 degrees C for all cross-linked films. When a PPh3 was used, the network properties were profoundly different. The base catalyzed thermoset of DGEBA and meta-DHB shows a T-g of 85 degrees C, which is 30 degrees C lower than the T-g of the acid-catalyzed analog. Tensile films appear to be more ductile, as they exhibit a strain-at-break of 20%. The results of this study confirm that simple dihydroxybenzene hardeners can be used to prepare cross-linked films with excellent thermomechanical properties.

A critical challenge for next-generation lithium-based batteries lies in development of electrolytes that enable thermal safety along with the use of high-energy-density electrodes. We describe molecular ionic composite electrolytes based on an aligned liquid crystalline polymer combined with ionic liquids and concentrated Li salt. This high strength (200 MPa) and non-flammable solid electrolyte possesses outstanding Li+ conductivity (1 mS cm−1 at 25 °C) and electrochemical stability (5.6 V versus Li|Li+) while suppressing dendrite growth and exhibiting low interfacial resistance (32 Ω cm2) and overpotentials (≤120 mV at 1 mA cm−2) during Li symmetric cell cycling. A heterogeneous salt doping process modifies a locally ordered polymer–ion assembly to incorporate an inter-grain network filled with defective LiFSI and LiBF4 nanocrystals, strongly enhancing Li+ conduction. This modular material fabrication platform shows promise for safe and high-energy-density energy storage and conversion applications, incorporating the fast transport of ceramic-like conductors with the superior flexibility of polymer electrolytes. Developing safe electrolytes compatible with high-energy-density electrodes is key for the next generation of lithium-based batteries. Stable solid-state rigid-rod polymer composite electrolytes with nanocrystalline lithium ion pathways are now proposed.

Solid-state electrolytes are attractive for use in electro-chemical devices because they remove the need for a flammable liquid electrolyte while contributing to the structural integrity of the device. We have recently developed a class of solid electrolytes, termed molecular ionic composites (MICs), composed of ionic liquids (ILs) and a rigid-rod polyelectrolyte, poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) (PBDT). MIC materials, originally obtained through an ion-exchange process between IL and PBDT aqueous solution, possess an unprecedented combination of high ionic conductivity, high thermal stability, low flammability, and widely tunable tensile storage moduli. Here we present a facile solvent casting method for preparing MIC membranes. These membranes are uniform, flexible, and tough, with tunable composition and thickness (>= 40 mu m). Unlike the previous ion-exchange method, which only allowed incorporation of hydrophilic ILs, we can now incorporate hydrophobic ILs to prepare MIC membranes for, for example, battery electrolytes. A sodium (Na) metal symmetric cell constructed with a PBDT-Pyr(14) TFSI membrane as the solid electrolyte shows long-term stable cycling (>500 h) at 60 degrees C. The ability to prepare MICs by using both hydrophilic and hydrophobic ILs initiates a wider range of MIC materials and broadens the array of applications accessible by MIC membranes.

Thermoplastic polyaryletherketones (PAEKs) exhibit excellent mechanical properties and fluid stability, but their glass transition temperatures (T-g) are low and their all-aromatic nature makes processing challenging. We will present a synthetic route toward phenylethynyl-functionalized hyperbranched PAEKs (hbPAEKs) (T-g = 151 degrees C) that can be cross-linked to form flexible films with high T-g's (187-237 degrees C) and good mechanical properties (E' = 4 GPa, sigma = 44 MPa, and epsilon = 1.76%). After cross-linking, the films are amorphous, easy to handle, and insoluble. We will report on the melt rheology of the hbPAEK precursors, with and without reactive phenylethynyl-reactive functionalities, and the thermomechanical characteristics of thin cross-linked films using dynamic mechanical thermal analysis, differential scanning calorimetry, and tensile testing. We believe that our findings can be extended to other all-aromatic structural and functional polymer architectures that are otherwise impossible to process.