Porous Materials

AEROGELS

First discovered by S.S. Kistler in the early 1930's, aerogels are extremely porous, lightweight solids (~0.01-0.1 g/cm3) that typically consist of over 90 vol% air. This property, in combination with their small pore sizes (10-40nm) and large internal surface areas, result in a material with very interesting properties. Most notably, aerogels are known for their ability to be excellent insulators with a thermal conductivity of less than 0.02 W/mK. Aerogels are created by first creating a wet gel (crosslinked material) through a sol-gel method followed by extraction of the liquid phase. A key component in the creation of aerogels is the minimization of surface tension within the pores of the solid phase to avoid collapsing of the pores during drying. Most often this is accomplished through the the use of novel methods such as supercritical fluid extraction (with CO2). In the more recent past, this has also been accomplished through freeze-drying (cryogels) and ambient drying with surface modification.

 

Poly(High Internal Phase Emulsion)s (PolyHIPEs)

Deforming the liquid droplets within an emulsion into a polyhedron shape enables the liquid to fill the space more efficiently and thus creating a more concentrated stable emulsion. The resulting emulsion is referred to as a high internal phase emulsion (HIPE). Polymerization of the dispersed phase, followed by extraction of this phase, results in the creation of an open-cell foam referred to as poly(HIPE)s. These porous foams have a highly interconnected pore network and consists of a dry material density of around 0.1 g/cm^3 and pore sizes around 30 micrometers or less. The poly(HIPE) foams can have application in many areas ranging from scaffolds for tissue engineering to beads for chromatography.

Selected Publications

Polyimide Cellulose Nanocrystal Composite Aerogels (2016)

Abstract:

Cellulose nanocrystals derived from tunicates (t-CNC) were used as a reinforcing nanofiller for polyimide aerogels. Two sets of polyimide aerogels, containing either 2,2′-dimethylbenzidine (DMBZ) or 4,4′-oxydianiline (ODA) and 3,3′,4,4′-biphenyltetracarboxylic acid dianhydride (BPDA) cross-linked with 1,3,5-tris(4-aminophenoxy)benzene (TAB), were studied. Total solids composition of the aerogels were kept constant at 7.5 wt %, with 0–13.33 wt % of the total solids being the carboxylic acid-functionalized t-CNC (t-CNC–COOH) filler. The incorporation of the t-CNC–COOH, with carboxylic acid content of either 560 or 920 mmol/kg, in the polyimide aerogel networks improved both physical and mechanical properties of the final materials. Isothermal aging of t-CNC–COOH aerogel composites was also conducted at 150 and 200 °C for 24 h. Higher content t-CNC–COOH/polyimide aerogels showed less change in their density and reduced shrinkage during aging, which further emphasized the effect of the t-CNC–COOH reinforcement in retaining the structural integrity of the aerogel.