Carboxylated core-shell particles: I. A system showing hindered swelling behavior

We study the swelling behavior of carboxylated core-shell particles. It is well-known that these particles swell with increasing pH due to the electrostatic repulsion between carboxylate groups. Our results reveal that the swelling behavior is affected by the preparation method. We find that the swelling is promoted in those particles which were initially in a highly swollen state (pH>or=10). However, the swelling is hindered for those particles which were not previously in this trigger pH. In the hindered systems, a compact conformation of the polymer shell is induced by hydrophobic attractions between the non-charged segments which compete against the swelling driving force. In addition, an interesting hysteresis behavior emerges when promoted systems are subjected to a heating-cooling cycle; a new stable system appears with a less extended polymer shell conformation. Furthermore, salt-induced swelling experiments corroborate not only polymer restructuring but also assembly among carboxylate groups which affects their ionization grade.