Morphology of latex and nanocomposite adsorbents prepared by freeze-casting

Abstract

Freeze-casting liquid dispersions of solid particles is a useful alternative for synthesizing porous solids, thus creating lightweight and mechanically resistant materials for various applications. This work describes and discusses different morphologies obtained by freeze-casting poly(styrene-acrylic) latex aqueous dispersions, either pristine or foamed, and compares them with those prepared by the addition of nanoclay. The surface area and dye sorption capacity of freeze-cast latex–clay nanocomposite monoliths are much higher than those of the freeze-cast latex only and the pore morphology is also different in these solids. The freeze-cast polymer displays an interesting morphology including a fishbone shape unprecedented in non-crystalline solids cast from aqueous media. Quite differently, the latex–clay nanocomposite exhibits only lamellar pores with irregular features on their walls. These differences are assigned to the stiffening role of the clay lamellae in the rubbery polymer, reducing the extent of particle aggregation and coalescence and thus preserving voids. Dispersion foaming prior to freeze-casting produces additional features in the solids but without making a positive contribution to the surface area and dye sorption capacity. These results are understood considering pore templating by ice crystal growth and the templating effect of clay particles on fine ice morphology.