Preparation of Soft Hydrogel Nanoparticles with PNIPAm Hair and Characterization of Their Temperature-Induced Aggregation

There exists a great number of publications concerning the synthesis of core−shell and/or hairy particles by means of controlled/living polymerization. Nevertheless, how to fabricate ultrafine nanosized hairy particles, especially polymeric soft hairy particles, remains a significant challenge. This paper presents a simple self-developed approach consisting of a two-step photoinduced polymerization of cross-linked polyacrylamide (CLPAM) soft hydrogel nanoparticles (5−10 nm in diameter) grafted with poly(N-isopropylacrylamide) (PNIPAm) chains. The architecture of such ultrafine soft water-swollen CLPAM@PNIPAm core/shell nanoparticles (20−35 nm in diameter) demonstrated very specific temperature sensitive behaviors. During heating a fast association process was observed at approximately 33−34 °C and the singular hairy particles with 34 nm diameters clustered into aggregates that were ∼120 nm in diameter. Raising the temperature further, however, led to a decrease in size to about 100 nm at 45 °C. This behav...