Next, to test if the condensation phenomenon that we observe in the hydrogel simulations is a consequence of conformational changes of the PE chains in the hydrogels, we run separate simulations with isolated, practi- cally infinite 25-mer single PAA chains constructed in a similar fashion with our hydrogel structure (see ). These chains are obtained by bonding one end of the chain to the other terminal monomer throughout the periodic boundaries. We define the λ = 0 state by considering the box dimensions at the isotropic pressure of P = 1.0 atm, similar to the hydrogel simulations. At this state, the chains are stretched, and their end-to-end distance is R 0 ≈ 6.2 nm. By stretching or compressing the simulation box, we stretch or compress the chain. This scheme allows us to control the end-to-end distance of the chain in the stretching/collapsing direction. In Figure . 4, we plot the percentage of condensed counterions for various stretching and compression cases as well as for λ = 0. The non-monotonic condensation profile that we observe for the hydrogel chains is qualitatively agreed with the singlechain case; the condensation exhibits a maximum at the weak stretching (i.e., λ ≈ 0.2). However, under weak compression and strong stretching (i.e., λ ≈ 0.5), counterions are less localized near the backbone charges, which results in a less number of condensed counterions (see Figure ).