Study of network composition in interpenetrating polymer networks of poly(N isopropylacrylamide) microgels: The role of poly(acrylic acid)

Hypothesis The peculiar swelling behaviour of poly(N-isopropylacrylamide) (PNIPAM)4PNIPAM: poly(N-isopropylacrylamide).4-based responsive microgels provides the possibility to tune both softness and volume fraction with temperature, making these systems of great interest for technological applications and theoretical implications. Their intriguing phase diagram can be even more complex if poly(acrylic acid) (PAAc)5PAAc: poly(acrylic acid).5 is interpenetrated within PNIPAM network to form Interpenetrating Polymer Network (IPN)6IPN: Interpenetrating Polymer Network.6 microgels that exhibit an additional pH-sensitivity. The effect of the PAAc/PNIPAM polymeric ratio on both swelling capability and dynamics is still matter of investigation. Experiments Here we investigate the role of PAAc in the behaviour of IPN microgels across the volume phase transition through dynamic light scattering (DLS),7DLS: Dynamic Light Scattering.7 transmission electron microscopy (TEM)8TEM: transmission electron microscopy.8 and electrophoretic measurements as a function of microgel concentration and pH. Findings Our results highlight that aggregation is favored at increasing weight concentration, PAAc content and pH and that a crossover PAAc content CPAAc∗9CPAAc: weight content (%) of the PAAc network within each IPN microgel.9 exists above which the ionic charges on the microgel become relevant. Moreover we show that the softness of IPN microgels can be tuned ad hoc by changing the PAAc/PNIPAM ratio. These findings provide new insights into the possibility to control experimentally aggregation properties, charge and softness of IPN microgels by varying PAAc content