Low-Density, Semicrystalline Poly(phenylene sulfide) Aerogels Fabricated Using a Benign Solvent

Abstract

Utilizing a thermally induced phase separation process, poly(phenylene sulfide) (PPS) thermoreversible gels are developed using for the first time a benign solvent, 1,3-diphenylacetone (DPA). The PPS/DPA phase diagram revealed a solid–liquid phase separation mechanism often observed with crystallizable polymers in good solvents. Two different methods of determining the Flory–Huggins interaction parameter, χ, were utilized to understand the polymer–solvent interactions that govern the phase behavior. Using an experimental approach, a melting point depression curve was fit to experimental PPS/DPA melting point data, revealing an interaction parameter of χ = 0.41. Using accepted Hansen solubility parameters of PPS and calculated parameters for DPA via a group contribution method, the polymer–solvent interaction parameter was estimated to be χ = 0.49. The reasonable agreement between both methods indicates good interactions between PPS and DPA and verifies the calculated solubility parameters for DPA. Upon gelation at temperatures below 225 °C, subsequent solvent evacuation via freeze–drying yields aerogels with low densities ranging from 0.11 to 0.25 g/cm3 and volumetric porosities ranging from 92.3 to 82.2%. The physical properties of the PPS aerogels were found to be comparable to similar aerogels made from poly(ether ether ketone) (PEEK). Ultra-small to wide-angle X-ray scattering (USAXS/SAXS/WAXS) profiles reveal an ordered, hierarchical morphology with sharp interfaces, whereby the microstructure is composed of semicrystalline aggregates of stacked lamella. Scanning electron microscopy micrographs indicate that the PPS aerogels are highly porous and that the lamellar stacks take the form of elongated, interconnected fibrils. Power-law scaling of aerogel density with compressive modulus suggests a tendency of the interconnected lamellar aggregates to bend and/or buckle in compression in a manner similar to strut deformation in open-celled foams. Despite their similar physical properties, PPS aerogels demonstrated higher moduli than PEEK aerogels at comparable densities due to their network-like morphology.

Separators and Membranes for Advanced Alkaline Water Electrolysis

“…A larger amount of DBS, accompanied by higher polymer concentration and faster cooling rate, could improve mechanical properties, such as tensile strength and elongation at break, of these membranes. Godshall et al 47 used a thermally induced phase separation process for developing PPS gels with a benign solvent, 1,3diphenylacetone (DPA). Gelation, which occurs at temperatures below 225 °C and is followed by freeze−drying solvent evacuation, results in formation of aerogels of low densities (0.11−0.25 g/cm 3 ) and high porosities (82.2−92.3%), with the structure of elongated, interconnected fibrils that could be of interest for development of future PPS AWE separators.…”

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

“…The solubility parameters for PEEK were calculated using the group contribution method of van Krevelen [80] as δ D1 = 18.8 MPa 1/2 , δ P1 = 4.3 MPa 1/2 , and δ H1 = 5.9 MPa 1/2 . Similarly, the solubility parameters for DPA were previously calculated by our group [28] using the group contribution method of Stefanis and Panayiotou [81]. The solubility parameters of DPA are δ D2 = 19.6 MPa 1/2 , δ P2 = 3.5 MPa 1/2 , and δ H2 = 4.7 MPa 1/2 .…”

“…Gels 2024, 10, 283 2 of 22 polyethylene [9][10][11], isotactic polypropylene [12,13], syndiotactic polystyrene [4,[14][15][16][17], poly(L-lactic acid) [18], polyoxymethylene [19], polyamide-6 [20], poly(vinylidene fluoride) [21,22], poly(ethylene terephthalate) [23], poly(phenylene oxide) [24,25], syndiotactic poly(methyl methacrylate) [26,27], and poly(phenylene sulfide) [28]. The choice of solvent can also lead to differences in the gel morphology and properties [29][30][31].…”

“…In contrast, 4CP and DCA are both acutely toxic, corrosive, and environmentally hazardous. Using DPA, we have previously reported the gelation of two other aromatic semicrystalline polymers: poly(phenylene sulfide) [28] (PPS) and poly(ether ketone ketone) [36] (PEKK). PPS and PEKK gels from DPA were found to contain fibrillar morphologies composed of crystalline axialites.…”

“…Liquid-liquid phase separation tends to have considerable composition dependence and can lead to morphologies such as powders [47] and bicontinuous structures [48,49]. Solid-liquid phase separation can lead to crystalline textures, such as spherulites [50][51][52][53] and axialites [28,52,53]. Porous PEEK systems have been prepared using solvents including 4-phenylphenol [54], diphenyl sulfone [55,56], and benzophenone [57].…”