In our previous paper, we found that there is a weak ion pairing between the functional group of the PMETAC brush [{N(CH3)3} + ] and the counterion (Cl -) due to a mismatch in their respective hydration shell strength. In other words, this weak ion pairing results from the water molecules being tightly bound to the Cl -ion and very weakly bound to the [{N(CH3)3} + ] group (owing to the apolar hydration inducing tendency of the three methyl groups). The phenomenon of weak ion pairing of counterions inside the PMETAC brushes has also been reported in experimental studies. These findings explain why there is a high mobility (or high velocity) of counterions