As previously noted, the ionization of the weak sites influences the microgel equilibrium size, shown in Fig. . In the simulations, we observe a nonmonotonic behavior of the swelling ratio α with increasing pH res . At low and intermediate pH res values, the microgels swell, driven by the increasing amount of counterions in the gel, reaching a maximum for pH res ≈ 9, where ζ a saturates. At high values of pH res , we observe again a decrease of α due to the increase of the ionic strength. This effect, which has also been observed in simulations of macroscopic gels, 7,8 was not captured in previous microgel simulations due to the use of the constant-pH method, which results in a wrong ionic strength at extreme pHvalues. A comparison with the swelling predictions of the theoretical model shows a close agreement with the simulations at low and high pH res , similar to the degree of ionization.