3.2. Morphological characterization
Assuming that the optical performance of this type of nanohybrids
is mainly attributable to their peculiar core–shell architecture,
we carried out a deep investigation on the morphological
characteristics of our sample. The TEM micrographs of drop-cast
films of H-Chit/AgNPs and bpPCDA/AgNPs aqueous suspensions
are illustrated in Fig. 3(a) and (b), respectively. Corresponding histograms
of the particle size distributions are reported alongside.
The image of the polysaccharide-protected sample shows the
presence of well-separated, nearly-spherical silver nuclei with an
average diameter of about 18 nm and a limited size dispersion,
in agreement with the profile of the SPR band of Fig. 1(a). More
complex features are evident in the picture of the polydiacetylenecovered
counterpart. In fact, although substantially unaltered in size (average diameter about 17 nm) and shape with respect
to the pristine ones, the metal cores appear mainly associated
into aggregates, while maintaining their individuality of primary
particles. These images suggest that silver nanoparticles may
be confined within structured organic material. AFM images
displayed in Fig. 4 show these structures.
AFM measurements were performed on the blue polymerized
colloids deposited on mica after being thoroughly purified from
small solutes by repeated dialysis against bi-distilled water.
Fig. 4(a) displays representative height and amplitude images
obtained by operating in tapping mode.
The presence of polydispersed, parallelepiped-like shaped
aggregates (‘‘bricks’’) is evident. The in-plane area and volume
distributions are reported alongside (Fig. 4(b)). Both histograms
show the same behavior, characterized by a main maximum at
around 1 × 104 nm2 and 1 × 106 nm3, respectively, and a tail
extending at higher values.