In Figs. 6 and 7 are presented the results for the production of
porous structures using nanocomposites prepared with alkylammonium
surfactants of different alkyl chains. The average pore
diameter decreased from 20.2m (neat polymer) to 5.7m for
the nanocomposite with the larger surfactant (PDLLA/C18MMT),
while the cell density increased almost one order of magnitude.
The production of structures with increased cell density and
smaller cell size can be attributed to the surface chemistry, which
affects the dispersion of nanoparticles in the PDLLA matrix (as suggested
from the XRD analysis) and, possibly, the MMT interaction
with supercritical CO2. The former leads to more sites available
for heterogeneous nucleation, because, even if the same nominal
nanoparticle concentration is used in all nanocomposites, their
effective concentration is higher once the nanoparticles are better
dispersed. As a consequence, more heterogeneous nucleation
sites are available for better dispersed samples (larger surfactants