To characterise whether polymer chains in aggregates were overlapping or not, and whether they were likely to be trapped in those structures, we have defined three order parameters: N pair , N total , and N trap , as illustrated in Fig. . For all three quantities, monomers were considered to overlap if their centre-of-mass separation was less than 7 Å. N pair defines the number of overlapping monomers between a given pair of polymer chains. A value < N (or N pair /N < 1), where N is the polymer chain length, indicates that two chains only overlap partially. N total extends this parameter to include the number of overlapping monomers between a chain and any other chain. Therefore, a value of N (or N total /N = 1) indicates either a pair of fully overlapping chains, or a chain that is fully covered by multiple other chains in a partially overlapping fashion. Finally we considered monomers to be trapped in an aggregated structure if they had a monomer on each face. N trap was thus defined as the number of monomers in aggregates that overlap with two other monomers on separate chains.