Reinforcing silica aerogels with tungsten disulfide nanotubes

Synthesis of silica aerogel films in liquid molds

By virtue of their low density and thermal conductivity, aerogels constitute attractive thermal insulators. Of those, aerogel films are best suited for thermal insulation in microsystems. Processes for the synthesis of aerogel films with thicknesses smaller than 2 µm or thicker than 1 mm are well established. However, for microsystems films in the range of a few microns and up to several hundred microns would be beneficial. To circumvent the present limitations, we describe a liquid mold made of two immiscible liquids, used here to produce aerogel films thicker than 2 µm in a single molding step. Following gelation and aging, the gels were removed from the liquids and dried using supercritical carbon dioxide. In contrast to spin/dip coating, liquid molding avoids solvent evaporation from the gel's outer surface during gelation and aging, films are free-standing and have smooth surfaces. The choice of liquids determines the aerogel film thickness. As a proof of concept, 130 µm thick homogeneous and high porosity (>90%) silica aerogel films were synthesized in a liquid mold with fluorine oil and octanol. The resemblance of the liquid mold approach to the float glass technique offers the prospect of mass production of large sheets of aerogel films.

Carbon Fiber-Silica Aerogel Composite with Enhanced Structural and Mechanical Properties Based on Water Glass and Ambient Pressure Drying

The article presents the synthesis of silica aerogel from a much cheaper precursor of water glass that was reinforced with short pitch carbon fiber by way of ambient pressure drying. Before being added to the silica gel, the carbon fibers were surface modified to increase adhesion at the interfacial border. We were able to obtain stable structures of the composite with the amount of fibers above 10% by volume. The presence of fibers in the silica matrix resulted in lower synthesis time of the composite, improved adhesion of fibers to the aerogel nanostructure, and increased mechanical and structural parameters. An additional effect of the presence of fibers in excess of 10% by volume was a new function of the nanocomposite—the ability to conduct electric current. The most optimal parameters of the composite, however, were obtained for silica aerogel reinforced with 10 vol.% of carbon fibers. This material indicated relatively low density and good physical parameters. The paper also analyzes the results on the synthesis of fiber-reinforced silica aerogels that have appeared in recent years and compares these to the results gained in presented work.

Nanocomposite of Poly(l-Lactic Acid) with Inorganic Nanotubes of WS2

Composites of poly(l-lactic acid) (PLLA) reinforced by adding inorganic nanotubes of tungsten disulfide (INT–WS2) were prepared by solvent casting. In addition to the pristine nanotubes, PLLA nanocomposites containing surface modified nanotubes were studied as well. Several surface-active agents, including polyethylene imine (PEI), were studied in this context. In addition, other biocompatible polymers, like poly d,l-lactic acid (PDLLA) and others were considered in combination with the INT–WS2. The nanotubes were added to the polymer in different proportions up to 3 wt %. The dispersion of the nanotubes in the nanocomposites were analyzed by several techniques, including X-ray tomography microscopy (Micro-XCT). Moreover, high-temperature rheological measurements of the molten polymer were conducted. In contrast to other nanoparticles, which lead to a considerable increase of the viscosity of the molten polymer, the WS2 nanotubes did not affect the viscosity significantly. They did not affect the complex viscosity of the molten PLLA phase, either. The mechanical and tribological properties of the nanocomposites were found to improve considerably by adding the nanotubes. A direct correlation was observed between the dispersion of the nanotubes in the polymer matrix and its mechanical properties.

Synthesis and Properties of Silica and Alginate Hybrid Aerogel Particles with Embedded Carbon Nanotubes (CNTs) for Selective Sorption

The manuscript describes methods for producing hybrid silica microparticles and hybrid alginate beads with carbon nanotube (CNT) contents up to 4.5 and 30 wt.%, respectively. Silica hybrid aerogel microparticles with embedded nanotubes were obtained using a two-stage sol–gel method with a gelling process in an oil-emulsion. Alginate hybrid aerogels with embedded nanotubes were obtained using cross-linking reactions. The following methods were used to measure the structural characteristics of obtained materials: nitrogen adsorption porosimetry, scanning electron microscopy (SEM), and others. It is shown that specific surface area and pore volume increase with the increase of CNT content in silica aerogel microparticles. Obtained aerogels were tested as adsorbents for argon–oxygen separation. The alginate hybrid aerogel with 30 wt.% CNT content has the best argon adsorption selectivity.

Recent Advances in Research on the Synthetic Fiber Based Silica Aerogel Nanocomposites

The presented paper contains a brief review on the synthesis and characterization of silica aerogels and its nanocomposites with nanofibers and fibers based on a literature study over the past twenty years and my own research. Particular attention is focused on carbon fiber-based silica aerogel nanocomposites. Silica aerogel is brittle in nature, therefore, it is necessary to improve this drawback, e.g., by polymer modification or fiber additives. Nevertheless, there are very few articles in the literature devoted to the synthesis of silica aerogel/fiber nanocomposites, especially those focusing on carbon fibers and nanofibers. Carbon fibers are very interesting materials, namely due to their special properties: high conductivity, high mechanical properties in relation to very low bulk densities, high thermal stability, and chemical resistance in the silica aerogel matrix, which can help enhance silica aerogel applications in the future.

From Fragile to Resilient Insulation: Synthesis and Characterization of Aramid-Honeycomb Reinforced Silica Aerogel Composite Materials

The production of a new composite material embedding aramid honeycomb materials into nano-porous silica aerogels is studied. Our aim is to improve the poor mechanical strength of silica aerogels by aramid honeycombs without losing the amazing properties of the aerogels like little density and low thermal conductivity. The composite materials were prepared using two formulations of silica aerogels in combination with aramid honeycomb materials of different cell sizes. The silica aerogels are prepared using silicon alkoxides methyltrimethoxysilane and tetraethylorthosilicate as precursors in a two-step acid⁻base sol⁻gel process. Shortly in advance of the gelation point, the aramid honeycombs were fluted by the sol, gelation occurred and, after the aging process, the gel bodies were supercritically dried. The properties of the received composite materials are satisfying. Even the thermal conductivities and the densities are a bit higher than for pure aerogels. Most importantly, the mechanical strength is improved by a factor of 2.3 compared to aramid honeycomb materials and by a factor of 10 compared to the two silica aerogels themselves. The composite materials have a good prospective to be used as an impressive insulation material.