  Carbonaceous nano-grains are present at the surface of protoplanetary disks
around Herbig Ae/Be stars, where most of the central star UV energy is
dissipated. Efficiently coupled to the gas, nano-grains are able to trace the
disk outer flaring parts, and possibly the gaps from which the larger grains
are missing. We examine the spatial distribution and evolution of the nano-dust
emission in the (pre-)transitional disk HD100546 that shows annular gaps,
rings, and spirals, and reveals rich carbon nano-dust spectroscopic signatures
(aromatic, aliphatic) in a wide spatial range (~20-200au). We analyse adaptive
optics spectroscopic observations from 3 to 4um and imaging and spectroscopic
observations from 8 to 12um. We compare the data to model predictions using the
THEMIS model with the radiative transfer code POLARIS calculating heating of
micro- and nanometric dust grains for a given disk structure. The aromatic
features at 3.3, 8.6 and 11.3um, as well as, the aliphatic ones from 3.4 to
3.5um are spatially extended with band morphologies dependong on local physical
conditions. The aliphatic-to-aromatic band ratio 3.4/3.3 increases with the
distance from the star suggesting UV processing. In the 8-12um observed
spectra, features characteristic of aromatic particles and crystalline
silicates are detected with their relative contribution changing with distance
to the star. The model predicts that the features and adjacent continuum are
due to different combinations of grain sub-populations, with a dependence on
the UV field intensity. Shorter wavelength features are dominated by the
smallest grains (< 0.7nm) throughout the disk, while at longer wavelengths what
dominates the emission close to the star is a mix of several grain populations,
and far away from the star is the largest nano-grain population.
