Influence of aromatic-rich carbon mantle thickness on amorphous silicate grains (for carbon grains with a 10 nm thick mantle). Models with no mantle (orange) and mantle thicknesses of 5 nm (turquoise), 7.5 nm (green), 10 nm (yellow), 15 nm (blue), and 20 nm (pink) are displayed. In panel a), the blue and pink lines are out of the plot with . The radiation field is also varied with . See Sect. 2.2 for description of the black and white lines and symbols.