Time-resolved polymer propagation for acrylic acid-mediated nanolatexes containing magnetic Fe₃O₄ cores

This study reports on the time-resolved polymer propagation of thermal-sensitive latex nanoparticles containing Fe₃O₄ cores. The latex shells are made with poly(N-isopropylacrylamide-co-acrylic acid) (Fe₃O₄/P(NIPAAm-co-AAc)) at different reaction times. The Fe₃O₄ particles are first modified using AAc monomers. The AAc-modified Fe₃O₄ cores are then copolymerized with NIPAAm to form the latex shell. The Fe₃O ₄ cores in the latex nanoparticles are confirmed using X-ray photoelectron spectroscopy (XPS), X-ray diffraction spectroscopy (XRD), and thermo gravimetric analyzer (TGA). As the reaction time is increased from 0.5 h to 2 h, the particle size enlarges from 100 to 250 nm and the Fe ₃O₄ content decreases from 46.4% to 2.6%. The thermal responses are more pronounced in the 2 h sample with the phase transition temperature (lower critical solution temperature, LCST) about 35 °C. The nanoparticles show a gradient concentration distribution of AAc as the particles propagate. A higher AAc concentration is observed near the Fe₃O ₄ core and the AAc content deceases as the degree of polymerization increases in the latex particles. This declining AAc concentration is beneficial for profound thermal responses in the synthesized nanoparticle.