Session G13: Aerogels, Foams and Sponges: Recent Advances and Challenges

Foams and aerogels based on nanopolysaccharides

Nanopolysaccharides, including nanocelluloses and nanochitin, self-assemble in aqueous solution and form gel networks, supramolecular inclusion complexes and other structures that adsorb at the oil/water and air/water interfaces. As such, they are ideally suited to stabilize multiphase systems such as Pickering emulgels and foams where the nanopolysaccharides bring their own functionalities. The latter can be extended by surface chemical modification or by combination with surfactants or polymers. Hence, it is possible to create stimuli-responsive, tailorable, and/or active functional bio-based materials suitable in a range of applications. We describe the chemistry, structure, and physicochemical properties of nanocellulose and deacetylated nanochitin for the synthesis of light-weight materials. We show the possibility of anisotropic and chiral nematic arrangement of cellulose nanocrystals to produce aerogels with opto-mechanical properties. In further developments, we describe 3D structured hybrid aerogels via liquid-liquid sculpting in which an elastic film formed at the interfaces of immiscible liquids leads to elastic structures with a highly porous honeycomb arrangement that is highly conductive upon thermal annealing and attenuate most of the incident EM waves. The aerogels act as perfect thermal insulators and infrared shields capable of preventing heat transfer, leading to effective energy saving and infrared shielding.   

Design & engineering of wood-inspired super-insulating foams

Buildings account for 40% of the total U.S. energy consumption. The energy lost through building’s walls, roofs and windows is the largest single waste of energy in most buildings. One way to contribute to the building energy efficiency consists in improving their thermal insulation by e.g., developing green and advanced functional materials as insulating panels.

With the advent of the Green Economy, the use and valorization of lignocellulosic biomass as a possible alternative of fossil resources is a promising approach for elaborating low cost and high value-added insulation materials. Proper deconstruction or fractionation of cell wall components has indeed been reported to facilitate the development of a wide range of high value materials. The extraction of high aspect ratio cellulose nanomaterials (CNMs) or nanocelluloses, from e.g., wood cell walls, is especially creating a revolution in biobased materials for diverse applications such as packaging, cosmetics, automotive and electronics, owing to their low density, large surface area, and high strength-to-weight ratio.

I will present our latest research on heat transport of fully bio-based foams and their thermal response as a function of relative humidity. The deconstruction of wood cell wall into cellulose nanofibers (CNFs) lays the foundation for the production of high-performance bio-based foams. I will discuss two engineering approaches to manufacture super-insulating foams: 1- the influence of chemical surface modification of CNFs on heat transfer of subsequent foams, and 2- the nature-inspired assembly of unmodified CNFs with another wood-biopolymer namely lignin, for enhanced performance.

This presentation aims to share an insight on the potential of wood-based foams as thermal insulation materials, but also to inspire scientists, researchers, and future generations to exploit the biomass beyond traditional end-use products, such as for the engineering and manufacturing of sustainable advanced functional materials for energy transfer, storage, or conversion.   

3D Printing of Aerogels

Aerogels exhibit unique properties such as ultra-low density, high and tunable porosity, large surface area, low thermal conductivity, refractive index, and low dielectric constant, which make them suitable for many applications including energy storage and conversion, catalysis, sensors, and bioengineering. The vision of tailoring the macrostructure of aerogels for broader applications has stimulated the research on the 3D printing of aerogels. Here, Dr. Lin and his collaborators propose a novel printing methodology, namely 3D freeze printing (3DFP), that combines multi-nozzle inkjet/extrusion printing with freeze casting for 3D printing of aerogels with several key qualities, including continuous, boundary-free, controlled alignment of porosity, and truly 3D structures (e.g., 3D objects with overhang features). A high-speed X-ray imaging technique has been applied to reveal the process dynamics in the 3DFP process. To date, the 3D printed aerogels have been successfully applied for Radomes for hypersonic vehicles, high-temperature ceramics, acoustic absorption, bone repair, energy storage, thermal insulation, chemical sensor, and chemical absorption.   

Polymer Aerogels: Advanced Porous Materials for Extreme Environments

As the Space Community endeavors to reach new heights of exploration, materials for extreme environment are on the forefront of research. One such material would include polymer aerogels; lightweight solids with nano-scale pore size, high internal surface area, low thermal conductivity, and extremely high porosities.  Due to these interesting properties, aerogels are ideal as thermal insulators but are by no means limited to this application. The high porosity and surface area also make aerogels an ideal host system for particle incorporation for applications such as IR filtration, sensor platforms, and vibro-acoustic mitigating materials.  Polymer aerogels also have the potential to combat issues found in extraterrestrial environments such as dust and radiation mitigation. Herein, current research will be discussed as it pertains to material capabilities in extreme environments.

    

Novel multifunctional aerogel materials from synergy of additive manufacturing and sol-gel processing

Many highly porous materials with pore volumes greater than 90% are attractive due to their high specific surface area and tunable surface energy. These materials cannot be easily adopted in advanced applications due to their poor mechanical strength and low handling stress. The advent of 3D-printing methods comes handy in such cases. The porous materials can be 3D-printed directly as metamaterials that offer much higher elongation and compliance in response to extensional stress than the parent porous materials themselves. The porous materials can also be made an integral part of 3D-printed, load bearing scaffolds to take advantage of their multi-functional attributes in thermal insulation, liquid-liquid separation, and nanoparticle removal from air with performance close to those of HEPA filters. This talk will illustrate three such examples. In one example, polyurethane aerogel metamaterials show substantially high elongation due to strategic arrangements of the highly porous limbs. In the second example, high porosity polyimide domains are grown inside or on surfaces of solid polymer scaffolds to produce excellent thermal insulation or provide efficient removal of noxious dye molecules from aqueous streams. In last example, variable surface energy strands of syndiotactic polystyrene or polyimide are used in removing water droplets from a hydrocarbon oil. Some generalizations will be made that other researchers can use and expand the concepts presented in this talk to an array of materials systems.