Fabrication and characterization of bifunctional spherical polyelectrolyte brushes

In this work, we prepared two kinds of dual-responsive spherical polyelectrolyte brushes (SPBs) with narrow distribution, of which cores were composed of polystyrene and grafting from copolymers of poly(N-isopropyl acrylamide-co-acrylic acid) (P(NIPAM-AA)) and poly(acrylic acid-co-N, N-diethyl acrylamide) (P(AA-DEA)), respectively. Both kinds of SPBs could response to pH and temperature stimulations by swelling/deswelling shell and electrophoretic mobility (EPM) changes. The low critical solution temperature of SPBs can be fine-tuned in the range of 28-45. at pH 3-9. Due to the different reactivity of comonomers (NIPAM and AA or DEA and AA), the acrylic acid (AA) unties were distributed at the inner shell of P(AA-DEA) and outer shell of P(NIPAM-AA), respectively, which led to different responses toward pH, temperature, and ionic strength, such as the abnormal 'salt effect' of P(AA-DEA) at low ionic strength and lower shell shrinkage ratio (SR) of P(NIPAM-AA). The dye adsorption in SPBs further confirmed the distribution of AA units.