The direct measurement of the polyPCDA layer thickness on
FE-SEM images provides different results. The mean diameter of
the silver cores, obtained from 21 isolated particles, is 23.5 nm
and the standard deviation is 6 nm. However, taking into account
the lower statistics and the partial overlap of the confidence
intervals, it is reasonable to conclude that these values agree with
those obtained by TEM images. The polyPCDA layer thickness
appears to be distributed around 5.3 nm (15 values) and 9.1 nm
(6 values), as reported in Figure 2Sb of Supporting Information.
The polymer thickness obtained from combining the TEM and DLS
measurements is smaller than that acquired from FE-SEM images.
Since Electronic Microscopy and DLS are quite different techniques
and in particular DLS values depend on the particle physical model,
comparison of the particle sizes measured by these techniques
deserves caution. Differences among microscopic and scattering
techniques can justify the discrepancy between the two values of
polyPCDA thickness we have obtained [39].
Taking into account these considerations, in Fig. 7 we propose
a model based on the data we obtained from FE-SEM images. In
this model either one or two superimposed diacetylene bilayers,
each of them composed by two rows of PCDA molecules oriented
with opposite polarity, are envisaged to surround the metal core.