Lauren S. White

Shortened aerogel fabrication times using an ethanol–water azeotrope as a gelation and drying solvent

Native and cross-linked aerogel monoliths were fabricated in a few hours using a technique that does not require solvent exchange prior to supercritical drying. Native oxide alcogels were synthesized by alkoxide hydrolysis–condensation using an ethanol–water azeotrope mixture as the gelation solvent. Cross-linked alcogels were synthesized by replacing part of the gelation solvent with a monomer, followed by visible light photopolymerization for which Eosin Y was used as an initiator and a tertiary amine used as a coinitiator. After aging for 2 hours, the alcogels were removed from the molds, placed in a pressure vessel, and dried using a supercritical ethanol–water azeotrope mixture. Starting from the sol, dried aerogels could be fabricated in about 6 hours. Most importantly, since solvent exchange was not required, native oxide and polymer cross-linked aerogels could be fabricated at the same rate. A systematic study was carried out to confirm that monoliths produced with our technique had density, surface area and Young’s modulus comparable to those of aerogels produced following more conventional pathways, such as supercritical CO2 drying. We synthesized samples using base- and acid-catalyzed chemistries, varied alkoxide concentration and, for cross-linked aerogels, monomer concentration. Depending on alkoxide concentration, native oxide aerogels had densities between about 0.06 and 0.17 g cm−3 and surface areas between about 300 and 500 m2 g−1. Depending on monomer type and concentration, cross-linked monoliths had a modulus between about 10 and 400 MPa, a density between 0.25 and 0.5 g cm−3 and a surface area between 150 m2 g−1 and 350 m2 g−1. Shrinkage was about 5% for base-catalyzed synthesis, about 20% for acid-catalyzed synthesis and about 10% for cross-linked monoliths. Infrared and Raman spectroscopies, solid state NMR and thermogravimetric analysis confirmed that drying in a supercritical ethanol–water azeotrope did not significantly affect the cross-linking polymer used to produce mechanically strong aerogels.

Fabrication of native silica, cross-linked, and hybrid aerogel monoliths with customized geometries

In this work, a previously developed (White et al 2015 J. Mater. Chem. A 3 762) rapid synthesis approach is used to fabricate native and cross-linked aerogel monoliths with customized geometries. This technique does not require solvent exchange, therefore fabrication times do not depend on part size. To prove this, parts with a smallest dimension of approximately 3.6 cm were fabricated within the same time scale as that of small cylinders with a diameter of 7 mm. In addition, monoliths with customized geometries exhibiting physical detail on the order of 1 mm were produced to demonstrate the versatility of this technique. Furthermore, hybrid materials consisting of native silica aerogel integrated with selected regions of polymer cross-linking were produced. The cross-linked regions allow for adhesion to other surfaces or labeling while the majority of the material retains the physical characteristics of a native silica aerogel. The physical and thermal properties of all aerogel components were examined. All aerogel materials produced in this work exhibited characteristics that were within the range of aerogel materials produced using more conventional methods. For native silica materials, this includes densities in the range of 0.03–0.116 g cm−3, surface areas between 342–799 m2 g−1, mode pore sizes in the range of 30–39 nm, and thermal conductivities in the range of 0.020–0.026 W m−1 K−1. For cross-linked aerogel materials, densities ranged between 0.154–0.340 g cm−3, surface areas were between 291–388 m2 g−1, mode pore sizes were in the range of 29–41 nm, and thermal conductivities were in range of 0.038–0.066 W m−1 K−1.

The anti-inflammatory properties of Au–scopoletin nanoconjugates

We investigated the biological activity of Au nanoparticles with a mean diameter of 30 nm which were capped with scopoletin, a natural coumarin isolated from Artemisia roxburghiana along with eleven other natural products. The NO inhibitory activity of scopoletin was unaffected by conjugation to the Au nanoparticles. A luminol chemiluminescence assay showed instead that conjugation increased the prevention of an oxidative burst of reactive oxygen species (ROS) in whole blood phagocytes and isolated neutrophils (PMN) by about three times.

Laser induced instantaneous gelation: aerogels for 3D printing

We present the synthesis of polymer cross-linked silica alcogels in a matter of seconds by illuminating the solution of TEOS, hexanedioldiacrylate, Eosin Y and amine with a laser beam (λ = 532 nm). The heat of polymerization triggers gelation instantly. We demonstrate printing of 3D letters on different substrates using this technique. The physical properties of the 3D printed samples are comparable to conventionally prepared cross-linked silica aerogels, i.e., shrinkage (10.4%), density (0.56 g cm−3), Youngs modulus (81.3 MPa) and BET surface area (155.3 m2 g−1). An important aspect of this rapid gelation is that it allows 3D printing/lithography of reinforced silica aerogel material without using a mould.

Fabrication of strong and ultra-lightweight silica-based aerogel materials with tailored properties

Cross-linked silica aerogels are promising, strong, lightweight materials for photolithographic applications. The work presented here details the preparation of ultra-lightweight aerogel materials with tailored properties through the appropriate combination of silica and methacrylate polymer using laser-induced rapid photogelation fabrication technique. For fabrication, an ethanolic solution of hexanediol diacrylate, tetraorthosilicate, Eosin Y and a tertiary amine was prepared. The amounts of reactants were varied to prepare different compositions of aerogel monoliths. The solution was irradiated with a green beam from a low power laser source. The samples, after drying in supercritical ethanol, were characterized using FTIR, BET, SEM, TGA, and a mechanical testing instrument. FTIR data suggests that neither low nor high silica content has an effect on the reactivity of acrylate functionalities during polymer formation. SEM micrographs reveal that variation in silica or polymer content does not produce any phase-separated structures. Instead, uniformly distributed nano-sized polymer–silica structures were obtained for all compositions. Our results suggest that a variety of combinations of mechanical and other properties (such as densities, surface areas, pore sizes, and pore volumes) can be produced through appropriate combination for diverse applications. All these findings provide convincing evidence that the variation of silica and/or polymer content can be used to fabricate aerogels with a variety of properties, which have the depth needed for use in laser-based 3D printing technology of simple or complex structures with nearly any dimensions.