Responsive catalysis of thermoresponsive micelle-supported gold nanoparticles

The block copolymer poly(N-isopropylacrylamide)-b-poly(4-vinyl pyridine) (PNIPAM-b-P4VP) self-assembled into core-corona micelles with the P4VP block as core and the thermoresponsive PNIPAM block as corona in water. The diameter of the micelles was about 40 nm and the lower critical solution temperature (LCST) was about 32 °C. Gold nanoparticles of size ranging from 2 to 4 nm were loaded in the micelles to form a responsive catalyst, the activity of which could be modulated due to the thermoresponsive PNIPAM. Below LCST, the PNIPAM chains were hydrophilic and the reactants could easily diffuse through the PNIPAM corona to reach the surface of the gold nanoparticles. Within this temperature range, the catalytic activity of the micelle-supported gold nanoparticles increased with the increase in temperature. Above LCST, the PNIPAM chains collapsed to form a hydrophobic barrier on the gold nanoparticles, which decelerated diffusion of the reactants. Within this temperature range, the activity of the micelle-supported gold nanoparticles decreased with the increase in temperature until to a minimum constant at about 38 °C.

Graphical abstractGold nanoparticles were loaded in thermoresponsive micelles of PS-b-PNIPAM to form a responsive catalyst. The catalytic activity of the responsive catalyst was modulated due to the thermoresponsive PNIPAM. Below LCST of the PNIPAM chains, the activity increased with the increase in temperature; above LCST, the activity decreased with the increase in temperature.Figure optionsDownload full-size imageDownload as PowerPoint slide