In all cases the calculated PDF functions of the composites fit well, with good correlation coefficients and C values close to zero (Table , Fig. ). Very similar to PC3, the residuals show correlations related to the empty capillary and additional peaks at 2.45 and 3.35 Å (Fig. ). These additional peaks are coincident with the Na•••N and Zn•••O•••P atomic distances compared to the literature (Fig. ), further supporting the N and 67 Zn MAS NMR data postulating these interactions. Features at 1.36 and 1.97 Å might be associated with ZIF-8 correlations (C•••C and C•••N, and Zn•••N). In fact, samples containing a higher amount of ZIF-8 in the composite have a greater contribution of both peaks. The negative peak at 1.63 Å, prob-ably from a mis-subtracted capillary contribution, corresponding to the Si-O bond in silicate glasses. These interactions compliment the H•••P correlations identified by MAS NMR (Fig 7 ). H•••P correlations are not observed by X-ray total scattering due to the low contribution of hydrogen atoms at the total PDF. This interaction at the interface might have a direct effect on the mechanical properties, increasing their strength.