Freeze-Casting For Facile Synthesis Of Novel Porous Materials
Freeze-casting is a method of synthesizing porous materials from mixtures comprised of a dispersed phase (colloidal and/or solutal) and a liquid dispersant, typically water. Cooling the mixture to temperatures below the freezing point of water causes nucleation and growth of ice crystals along the thermal gradient. Exclusion of the dispersed phase results in the formation of two interpenetrating networks upon complete solidification of the water - one made from ice, the other comprised of the rejected colloid and/or solute. Removal of the ice via freeze-drying produces a structure made from the excluded phase, with micron-sized pores created by the ice template. This work will address the use of freeze-casting for facile synthesis of porous structures with tunable porosity, mechanical properties, and structural (bonding) order. The first part of this work is concerned with the use of freeze-casting in the preparation of porous scaffolds prepared from poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate), PEDOT:PSS, a semiconducting polymer complex. Aqueous dispersions of PEDOT:PSS were freeze-cast under a variety of conditions to examine the impact of dispersion concentration/composition and freezing conditions on the morphology and mechanical properties of the scaffold. Finally, PEDOT:PSS monoliths with appropriate porosity and mechanical robustness were used to study the electrical control of cell deposition in a 3D matrix. ! The remainder of this work addresses the use of freeze-casting for the synthesis of hierarchical porous carbons (HPCs) prepared from various organic precursors. Hierarchical structure is generated through the use of an ice template, colloidal SiO2, and physical activation of the carbon. The impact of carbon precursor (glucose, sucrose, resorcinol, and resorcinol formaldehyde), SiO2 template, and freeze-casting conditions on the morphology and structural order was examined. Interestingly, the dispersion composition impacted the porosity generated by both the ice template and SiO2 particles via behavior akin to constitutional supercooling as observed in alloys. Additionally, the templating efficacy of the colloidal SiO2 was found to impact the structural order observed in the as-produced carbon. !
Materials Science; Freeze Casting; Porous Materials
Materials Science and Engineering
Ph. D., Materials Science and Engineering
Doctor of Philosophy
dissertation or thesis