More Like this

1. Scalable, hydrophobic and highly-stretchable poly(isocyanurate–urethane) aerogels

   https://doi.org/10.1039/c8ra03085e  

   Malakooti, Sadeq; Rostami, Saman; Churu, Habel Gitogo; Luo, Huiyang; Clark, Jenna; Casarez, Fabiola; Rettenmaier, Owen; Daryadel, Soheil; Minary-Jolandan, Majid; Sotiriou-Leventis, Chariklia; et al (January 2018, RSC Advances)

   Scalable, low-density and flexible aerogels offer a unique combination of excellent mechanical properties and scalable manufacturability. Herein, we report the fabrication of a family of low-density, ambient-dried and hydrophobic poly(isocyanurate–urethane) aerogels derived from a triisocyanate precursor. The bulk densities ranged from 0.28 to 0.37 g cm −3 with porosities above 70% v/v. The aerogels exhibit a highly stretchable behavior with a rapid increase in the Young's modulus with bulk density (slope of log–log plot > 6.0). In addition, the aerogels are very compressible (more than 80% compressive strain) with high shape recovery rate (more than 80% recovery in 30 s). Under tension even at high strains ( e.g. , more than 100% tensile strain), the aerogels at lower densities do not display a significant lateral contraction and have a Poisson's ratio of only 0.22. Under dynamic conditions, the properties ( e.g. , complex moduli and dynamic stress–strain curves) are highly frequency- and rate-dependent, particularly in the Hopkinson pressure bar experiment where in comparison with quasi-static compression results, the properties such as mechanical strength were three orders of magnitude stiffer. The attained outcome of this work supports a basis on the understanding of the fundamental mechanical behavior of a scalable organic aerogel with potential in engineering applications including damping, energy absorption, and substrates for flexible devices. 

   more » « less
2. Additive Manufacturing of Poly(phenylene Sulfide) Aerogels via Simultaneous Material Extrusion and Thermally Induced Phase Separation

   https://doi.org/10.1002/adma.202307881  

   Godshall, Garrett F; Rau, Daniel A; Williams, Christopher B; Moore, Robert B (August 2024, Advanced Materials)

   Abstract 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. 

   more » « less
3. Shear thickening in dense bidisperse suspensions

   https://doi.org/10.1122/8.0000495  

   Malbranche, Nelya; Chakraborty, Bulbul; Morris, Jeffrey F. (January 2023, Journal of Rheology)

   Discrete-particle simulations of bidisperse shear thickening suspensions are reported. The work considers two packing parameters, the large-to-small particle radius ratio ranging from [Formula: see text] (nearly monodisperse) to [Formula: see text], and the large particle fraction of the total solid loading with values [Formula: see text], 0.5, and 0.85. Particle-scale simulations are performed over a broad range of shear stresses using a simulation model for spherical particles accounting for short-range lubrication forces, frictional interaction, and repulsion between particles. The variation of rheological properties and the maximum packing fraction [Formula: see text] with shear stress [Formula: see text] are reported. At a fixed volume fraction [Formula: see text], bidispersity decreases the suspension relative viscosity [Formula: see text], where [Formula: see text] is the suspension viscosity and [Formula: see text] is the suspending fluid viscosity, over the entire range of shear stresses studied. However, under low shear stress conditions, the suspension exhibits an unusual rheological behavior: the minimum viscosity does not occur as expected at [Formula: see text], but instead decreases with further increase of [Formula: see text] to [Formula: see text]. The second normal stress difference [Formula: see text] acts similarly. This behavior is caused by particles ordering into a layered structure, as is also reflected by the zero slope with respect to time of the mean-square displacement in the velocity gradient direction. The relative viscosity [Formula: see text] of bidisperse rate-dependent suspensions can be predicted by a power law linking it to [Formula: see text], [Formula: see text] in both low and high shear stress regimes. The agreement between the power law and experimental data from literature demonstrates that the model captures well the effect of particle size distribution, showing that viscosity roughly collapses onto a single master curve when plotted against the reduced volume fraction [Formula: see text]. 

   more » « less
4. Aesthetic Aerogel Window Design for Sustainable Buildings

   https://doi.org/10.3390/su14052887  

   Carroll, Mary; Anderson, Ann; Mangu, Sri; Hajjaj, Zineb; Capron, Margeaux (March 2022, Sustainability)

   Transport of heat through windows accounts for more than 25% of heating and cooling losses in residential buildings. Silica-based aerogels are translucent with extremely low thermal conductivity, which make them attractive for incorporation into the interspaces of glazing units. Widespread incorporation of monolithic-silica-aerogel-based windows could result in significant energy savings associated with the heating and cooling of buildings. However, monolithic silica aerogels do not have the optical clarity of vision glass, due to light scattering by the solid matrix, and often have surface imperfections, both of which render these materials less appealing for glazing applications. Here, we demonstrate a variety of approaches to preparing aesthetically pleasing monolithic silica aerogel by a rapid supercritical extraction method for incorporation into glazing units, including: (1) process improvements that result in monoliths with higher visible light transmission; (2) innovative mold design for the preparation of uniform aerogel monoliths; (3) glazing designs that use thinner monoliths; and (4) the incorporation of artistic effects using dyes and laser etching to prepare glazing units with mosaic- or stained-glass-like patterns in which surface imperfections are perceived as features of the design rather than flaws. 

   more » « less
5. High Modulus, Strut-like poly(ether ether ketone) Aerogels Produced from a Benign Solvent

   https://doi.org/10.3390/gels10040283  

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

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

   more » « less