Capitalizing on the opportunities presented by the controlled confined synthesis within the hydrophobic micellar core, we conducted time-resolved DLS and small-angle X-ray scattering (SAXS) measurements during the formation of the colloidal solution to gain unprecedented insights into the growth mechanism of COF-300 at the nanoscale. We decided to study the growth mechanism of COF-300 nanoparticles in the absence of the modulator to simplify the reaction mechanism. As indicated above, the DLS analysis of the two micellar solutions containing the COF precursors give comparable results to those obtained for pure CTAB/SDS mixed micelles. However, upon mixing the two micellar solutions containing the COF precursors, and upon the addition of the catalyst, notable changes in the DLS measurements and SAXS profiles were observed over time. Note that while the DLS measurements conducted on the reaction mixture showcased a progressive increase in the hydrodynamic diameter of the COF-300 nanoparticles over time, reaching a steady state at around 40 nm (Figure ), no substantial changes in the scattering profiles were obtained with the SAXS measurements during the initial 10 hours of reaction. However, after 10 hours of reaction clear changes in the SAXS spectra were also observed, allowing for the investigation of the growth mechanism of the COF-300 nanoparticles over time. The SAXS scattering profiles obtained at two specific time points, namely the initial stage (10 hours) and the final stage (42 hours), are shown in Figure and 3B, respectively. The obtained scattering values were subjected to fitting using a three-layer spherical model, comprising the core of the COF-300 nanoparticles, a hydrophobic layer that includes the alkyl chains of the surfactants, and a hydrophilic layer composed of the polar heads of the surfactants (more information of the model can be found in SI). The fitting of the scattering profiles with the model clearly demonstrates an increase in intensity and a change in the slope at low scattering angles (q < 1 nm -1 ) that indicate a progressive enlargement of the particle diameter from 29 nm to 40 nm during this time period accompanied by an increase of the volume fraction (see also Figure and Table ).