Tailoring of Morphology and Surface Properties of\nSyndiotactic Polystyrene Aerogels

Abstract

This\nstudy evaluates a method for rendering syndiotactic polystyrene\n(sPS) aerogels hydrophilic using polyethylene oxide (PEO) of different\nmolecular weights. The highly porous sPS aerogels are inherently hydrophobic\nalthough applications involving absorption of moisture and removal\nof particulate solids may benefit from the high surface area of sPS\naerogels provided some degree of hydrophilicity is induced in these\nmaterials. In this work, sPS gels are prepared by thermo-reversible\ngelation in tetrahydrofuran in the presence of PEO. The gels are dried\nunder supercritical conditions to obtain aerogels. The aerogels are\ncharacterized by scanning electron microscopy, nitrogen-adsorption\nporosimetry, helium pycnometry, and contact angle measurements. The\ndata reveal that the pore structures and surface energy can be controlled\nby varying the concentration and molecular weight of PEO and using\ndifferent cooling rates during thermo-reversible gelation. In the\nfirst case, sPS aerogels, aerogels containing PEO of a low molecular\nweight or low concentration show superhydrophobic surface presenting\nthe “lotus effect”. In the second case, PEO at a higher\nconcentration or with higher molecular weight forms phase-separated\ndomains yielding new hydrophilic macropores (>10 μm) in the\naerogel structures. These macropores contribute to the superhydrophobic\nsurface with the “petal effect”. The cooling rate during\ngelation shows a strong influence on these two cases.