Freezedrying Silica Based Aerogels Using Cryoprotectants and Eutectic

Freeze-drying Silica Based Aerogels Using Cryoprotectants and Eutectic Solvent Mixtures Alyssa Bass, Shane Peng, and Jeffrey Youngblood School of Materials Engineering, Purdue University, West Lafayette, IN, USA INTRODUCTION RESULTS § Silica aerogels are a unique class of light-weight, structurally strong materials with properties like high porosity and low density. § Silica aerogels can be used in multiple applications as seen in Figure 1. § Current drying methods used to produce aerogels require specialized equipment and are time consuming. § Simpler, more cost effective methods for drying wet gels are needed. § White, monolithic foams were produced with different cryoprotectant mixtures. Untreated 10% PVP Figure 2. Progression from untreated, to below optimum concentration, to optimum concentration. 10% Ammonium 25% citric acid Carbonate 10% PVP Figure 1. Map detailing potential uses for Aerogels [2]. 5% PVP 3% PVA 10% PVP 10% Citric Acid Figure 3. Monolithic foams produced from various treatments. SEM 30 µm § A sol-gel process developed by Tamon, et al. [1] was modified and used. Syringe mold 10% PVP 10% (NH 4)2 CO 3 25% Citric Acid 3% Ethanol Adsorption Bulk Avg. Pore Density Diameter 4. 9806 nm 0. 220 g/cm³ 78. 6314 m²/g 72. 1586 m²/g 4. 8005 nm 0. 212 g/cm³ 50. 5059 m²/g 637. 9697 m²/g 870. 5 m²/g 8. 2472 nm 0. 384 g/cm³ 4. 4342 nm 0. 125 g/cm³ 3. 6867 nm 0. 017 g/cm³ N/A 0. 128 g/cm³ 3% Ethanol 20% Citric Acid Figure 4. SEM images of dried gels, with various treatments, showing good pore size, distribution and connectivity. § Addition of cryoprotectant and polymer solutions can produce monolithic, white foams. § Addition of eutectics, such as ethanol, leads to good pore size, distribution, and connectivity, with poor monolithicity. § Better monolithicity does not necessarily yield better pores. FUTURE WORK 2. Base catalyzed Sol-gel step § Affects of more eutectic mixtures on silica gels after freeze-drying will be studied for affects on pore size and monolithicity. § Combinations of eutectics, cryoprotectants, polymers, and ice structuring proteins/substances will be tested. 3. Gelation 5 -10 mins Stir while adding 7% NH 4 OH Soln. then add to mold. 1. Acidcatalyzed Sol formation 6. Analysis by optical microscopy, BET, and SEM. 50% Ethylene Glycol 10% PVP BET Surface Area 291. 8944 m²/g CONCLUSIONS 30 µm Washed, aged, then 10% PVP, 0. 25% Xanthan gum solution Treatment Super. Critical Dry [3] 80 µm METHODS BET 30 µm 5% Citric Acid 5. Freeze. Drying 4. Solvent exchange by soaking in solutions. 20 µm 5% Ethanol 50 µm 50% Ethanol 50% Water solution Figure 4. SEM images of dried gels, with various treatments, showing poor pore size, distribution and connectivity. REFERENCES 1. Tamon, H. , Kitamura, T. , and Okazaki, M. "Preparation of Silica Aerogel from TEOS. " Journal of Colloid and Interface Science, Vol. 197. 2, 1998, pp. 353 -59. 2. Schmidt, M. , and Schwertfeger, F. “Applications for Silica Aerogel Products. ” Journal of Non. Crystalline Solids, Vol. 225, 1998, pp. 364 -368. 3. Błaszczyński, T. , Ślosarczyk, A. , and Morawski, M. "Synthesis of Silica Aerogel by Supercritical Drying Method. " Procedia Engineering, Vol. 57, 2013, pp 200 -06.