Reversible Clustering of pH- and Temperature-Responsive Janus Magnetic Nanoparticles

Abstract

Janus nanoparticles have been synthesized consisting of approximately 5 nm magnetite nanoparticles coated on one side with a pH-dependent and temperature-independent polymer (poly(acrylic acid), PAA), and functionalized on the other side by a second (tail) polymer that is either a pH-independent polymer (polystyrene sodium sulfonate, PSSNa) or a temperature-dependent polymer (poly(N-isopropyl acrylamide), PNIPAM). These Janus nanoparticles are dispersed stably as individual particles at high pH values and low temperatures, but can self-assemble at low pH values (PSSNa) or at high temperatures (>31 degrees C) (PNIPAM) to form stable dispersions of clusters of approximately 80-100 nm in hydrodynamic diameter. The Janus nanoparticle compositions were verified using FTIR and XPS, and their structures observed directly by TEM. Their clustering behavior is analyzed by dynamic light scattering and zeta potential measurements.

Polymeric Janus Particles

“…The carboxylic acid groups on the exposed particle surface were subsequently reacted with amine-terminated polymers (poly(styrene sulfonate) (PSSNa) or poly(N-isopropyl acrylamide) (PNIPAM)) to create the Janus particle. [81] Temperature-dependent (PNIPAM) or pH-dependent (PSSNa) aggregation of the Janus particles was observed.…”

Molecular Mimetic Self‐Assembly of Colloidal Particles

“…[148,149] Hatton has presented elegant Janus nanoparticles, 5 nm magnetite nanoparticles with one hemisphere coated pH-sensitive polyacrylic acid and the other coated with either pH-insensitive PS sulfonate or temperature-sensitive poly(N-isopropyl acrylamide). [150] These Janus nanoparticles were well-dispersed at pH 10 or temperature below 31 8C, but self-assembled to 80-100 nm clusters at pH 2 or at temperatures above 31 8C due to the enhanced hydrophobic interaction between the particles.…”

Stimulus-responsive polymeric nanoparticles for biomedical applications

“…To overcome this limitation, Isojima et al [103] developed thermal/pH/magnetic triple nanoparticles with separated thermal and pH parts in the nanoparticles, in which thermal and pH parts were located on two hemispheres of the nanoparticles. Nanoparticles with this special structure are usually denoted as Janus nanoparticles and their self-assembling behavior under different stimuli is shown in Figure 8.…”

“…Its CO bond could be heterolytically cleaved to form colored merocyanine under the irradiation of UV light, during which the light-induced color change was realized. Garcia developed new triple- Figure 8 Schematic representation of the Janus nanoparticles and their self-assembled behavior under different stimuli [103]. responsive nanoparticles by attaching photo-responsive spiropyran onto the thermal/pH responsive microgels based on PNIPAAm-allylamine [104].…”