Figure 1.

Core–shell and hollow microgels in bulk aqueous suspensions: core degradation process. (a) Simulation snapshots of the cross section of a core–shell microgel before and after the removal of the inner core. The core with the DHEA cross-linker is colored in blue, and the outer shell with the BIS cross-linker is colored in green/yellow. (b) Extent of core removal X as a function of n·t, where n is the NaIO₄ to DHEA molar ratio and t is the reaction time. The symbols indicate the values of X estimated from the experimental form factors (see Materials, Models, and Methods), whereas the lines show eq 2 fitted to the experimental X for different values of n. (c) Hydrodynamic diameter D_h of core–shell microgels as a function of the extent of core removal X. The horizontal dashed lines emphasize the sudden transition to a larger dimension upon removal of a critical core fraction. (d) Experimental (symbols) and numerical (lines) form factors as a function of the wavenumber q. The experimental form factors are for n·t = 0, 20, 144, and 9600, whereas the numerical ones are calculated for different number densities of the core microgel: ρ ≈ 0.08, 0.06, and 0.01 σ^–3 (from the bottom to the top), where σ, representing the monomer size, is the unit length in the simulations. The yellow circles correspond to the hollow microgel (X = 100%). The form factors are arbitrarily shifted along the y-axis for visual clarity. The symbols in (c) and (d) correspond to the same values of n shown in (b), with * black symbols indicating the core–shell microgel prior to core removal (n = 0).