Using supercritical carbon dioxide (Sc-CO2) as the physical foaming agent

polystyrene (PS) foams were prepared in a batch process via two different heating modes and depressurization.The cellular structures

foam densities and wetting properties of the PS foams were investigated by means of scanning electron microscope

electronic balance and contact angle measuring device

respectively.The results showed that a mono-modal cell structure was obtained only through depressurization

whereas a bi-modal cell structure was achieved through the synergistic effect of heating and depressurization.The large and small cells were formed by nucleation in the heating and depressurization stages

respectively.For the PS foams prepared at 100 ℃ foaming temperature and 30~70 ℃ saturation temperatures

the large and small cells had average diameters of 50~216 and 10~15 m

respectively.Increasing the diameter and density of the large cell was favourable to the decrease of the foam density

and the lowest foam density was 0.15 g/cm3.The mono-modal cell structure yielded an increase in static contact angle (CA) from the intrinsic value of the PS (87.1) to 138.8 on the fractured surface of the foam; the CA value on the surface with a bi-modal cell structure prepared at 70 ℃ saturation temperature increased up to 155.1

displaying the superhydrophobic wetting properties.