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

TL;DR

This study explores how incorporating poly(acrylic acid) into poly(N-isopropylacrylamide) microgels affects their swelling, charge, and aggregation behavior, revealing ways to tune their properties for technological applications.

Contribution

It provides new insights into how PAAc content influences the swelling, charge, and aggregation of IPN microgels, enabling tailored property control.

Findings

Aggregation increases with concentration, PAAc content, and pH.

A critical PAAc content C*_{PAAc} affects ionic charge relevance.

Microgel softness can be tuned by PAAc/PNIPAM ratio.

Abstract

Hypothesis: The peculiar swelling behaviour of poly(N-isopropylacrylamide) (PNIPAM)-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) is interpenetrated within PNIPAM network to form Interpenetrating Polymer Network (IPN) 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), transmission electron microscopy (TEM) 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 C*_{PAAc} 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.