Figure 15.

Probing the hydrophobic collapse of grafted polystyrene chains on gold nanoparticles in THF upon mixing with water. Initially, repulsive particles became attractive and clustered upon collapse of the grafted chains. (a) Schematic representation of the 3D flow-focusing microfluidic reactor with a middle channel (MC) and two side channels (SC), and the simulated concentration pattern of THF/water mixture. The X-ray beam passed orthogonal to the flow and the lateral focusing directions. (b) Evolution of the SAXS profiles of the particles as a function of the distance from the mixing point ($X_C$) for a flow rate ratio (FRR) of 2. The peak corresponds to the structure factor of the particles upon clustering and modeling of which provided an effective size of particles. (c) The variation of effective particle radius as a function of $X_C$, which is equivalent to a residence time ($t_{res}$) given by the flow rate, for different FRR. The chain collapse transition occurred in the millisecond time scale. Adapted from S. Merkens et al. [127] with permission from the American Chemical Society, ©ACS 2019.