Figure 3.

(a) Mean pore diameter as a function of saturation pressure. Pressures above 30 MPa result in pore diameters in the nanometer range, which does not decrease for higher pressures. The pressure range giving the whitest films, i.e. dense, homogeneous, sub-nanometer sized pores, is shadowed. (b) SEM images of the foamed films for three applied pressures, indicated above the images. We observed an increase of pore homogeneity for high pressures, i.e. above 30 MPa, and insignificant change in morphology for higher pressures.