Tunable attractive and repulsive interactions between pH-responsive microgels

We report direct measurements of the pairwise interparticle potential between poly(N-isopropylacrylamide-co-acrylic acid) (pNIP Am-co-AAc) colloidal microgels as a function of pH, as determined through Ornstein-Zernike analysis of the pair distribution function of quasi-2D dilute colloidal suspensions. The interaction potential ranges from purely repulsive at high pH due to electrosteric interactions to weakly attractive at low pH due to hydrogen bonding, which explains previous observations on the unique phase behavior of these particles in concentrated suspensions.