The first PC (PC1) largely corresponds to glass correlations, whilst the second (PC2) matches the PDF from ZIF-8 (Fig. ). However, the third component (PC3) does not fit with either, and exhibits features at short-r value similar to those from a PDF from the empty capillary. There is also a small additional peak at 2.18 Å and a stronger negative peak at 3.44 Å (Fig. ). The weightings of PC1 follow the negative trend with the minor amount of glass in the composite, whilst weightings of PC2 exhibit a positive linear trend with the increment of ZIF-8 in the composite (Fig. ). However, the weightings of PC3 have a higher contribution (in absolute value) for the composites than the pristine materials. The negative weighting to PC3 for the composites suggests that -PC3 may be the more physically relevant function, i.e. the empty capillary may have been over-subtracted in the data normalisation and there is potentially the interaction at the interface, with a positive feature at 3.40 Å, which might be related to the interaction P-O-Zn between the ZIF-8 and the glass at the interface (Fig. ).