Aggregation behavior of pH- and thermo-responsive block copolymer protected gold nanoparticles

Two distinctive block copolymers protected gold nanoparticles (AuNPs) were prepared with poly(methylacrylic acid)-block-poly(N-isopropylacrylamide) (SH-PMAA(64)-b-PNIPAM(35)) and poly (N-isopropylacrylamide)-block-poly(methylacrylic acid) (SH-PNIPAM(40)-b- PMAA(60)) through strong gold-sulfur bonding. The hybrid NPs have a pH-responsive inner shell (or corona) and a thermo-responsive corona (or inner shell) due to different location relations of the PNIPAM and PMAA on the surface of AuNPs. Then, the aggregation behaviors, as well as the changes of optical properties, of two hybrid NPs were compared in response to both stimuli. The results showed the obvious inter-particle aggregation caused by the phase transition for hydrophobic coronal polymer. However, the particles of hydrophilic corona layer retained good dispersion and the pH-responsive or thermo-responsive characteristics of shell layer made relatively minor changes.