  We present a systematic study of mid-infrared spectra of galaxies including
star-forming galaxies and Active Galactic Nuclei observed with JWST MIRI-MRS
and NIRSpec-IFU. We focus on the relative variations of the 3.3, 6.2, 7.7,
11.3, 12.7 and 17 micron Polycyclic Aromatic Hydrocarbon (PAH) features within
spatially resolved regions of galaxies including NGC 3256, NGC 7469, VV 114, II
Zw96 and NGC 5728. Using theoretical PAH models and extending our earlier work,
we introduce a new PAH diagnostic involving the 17 micron PAH feature. To
determine the drivers of PAH band variations in galaxies, we compare observed
PAH spectral bands to predictions from theoretical PAH models. We consider
extinction, dehydrogenation and PAH size and charge as possible drivers of PAH
band variations. We find a surprising uniformity in PAH size distribution among
the spatially resolved regions of the galaxies studied here, with no evidence
for preferential destruction of the smallest grains, contrary to earlier
findings. Neither extinction nor dehydrogenation play a crucial role in setting
the observed PAH bands. Instead, we find that PAH charge plays a significant
role in PAH inter-band variations. We find a tight relation between PAH charge
and the intensity of the radiation field as traced by the [NeIII]/[NeII] maps.
In agreement with recent JWST results, we find a predominance of neutral PAH
molecules in the nuclei of Active Galaxies and their outflows. Ionised PAHs are
the dominant population in star-forming galaxies. We discuss the implications
of our findings for the use of PAHs as ISM tracers in high redshift galaxies.
