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

Area of Science:

• Materials Science
• Polymer Chemistry
• Physical Chemistry

Background:

• Carboxylated core-shell particles are known to swell with increasing pH.
• This swelling is driven by electrostatic repulsion between ionized carboxylate groups.

Purpose of the Study:

• To investigate the influence of preparation method on the swelling behavior of carboxylated core-shell particles.
• To elucidate the mechanisms governing swelling under different pH and ionic conditions.

Main Methods:

• Synthesis and characterization of carboxylated core-shell particles.
• pH-dependent swelling studies.
• Heating-cooling cycle experiments to observe hysteresis.
• Salt-induced swelling experiments to probe polymer restructuring and group assembly.

Main Results:

• Swelling is promoted in particles previously exposed to high pH (>=10).
• Swelling is hindered in particles not exposed to high pH, with hydrophobic attractions inducing compact conformations.
• Hysteresis behavior observed upon heating-cooling cycles in promoted systems, leading to a less extended polymer shell.
• Salt-induced swelling indicates polymer restructuring and carboxylate group assembly, affecting ionization.

Conclusions:

• The preparation method and prior pH history are critical factors controlling particle swelling.
• Hydrophobic interactions play a significant role in hindering swelling under specific conditions.
• Complex phenomena like hysteresis and salt-induced restructuring highlight the dynamic nature of these polymer systems.