## 3 Results and Discussion
The average particle size measured using flow cell coupled DLS with 3D modulation is 157 nm for the large particles and 16.2 nm for the small particles. Thus, the measurement results obtained with conventional DLS and DLS with 3D cross correlation geometry performed at Q = 0 mL-min\({}^{-1}\) are in excellent agreement. Furthermore, both for the large and small particles the particle size measured using DLS with 3D cross correlation geometry remains nearly constant for flow rates up to 17 mL-min\({}^{-1}\). Thus, through the use of a modulated 3D cross correlation DLS instrument, we were able to accurately analyze dispersions comprising differently sized silica nanoparticles at flow rates up to 17 mL-min\({}^{-1}\). During the synthesis of the large and small silica nanoparticles, starting from the molecular precursor TEOS, the particle growth was monitored in real time using the analysis loop connected to the 3D cross correlation DLS unit (Figure 4a,b). Figure 4: _Cont._  
Figure 3: Particle size measurement using the DLS with 3D cross correlation geometry of (**a**) “large” SiO\({}_{2}\) nanoparticles; (**b**) “small” SiO\({}_{2}\) nanoparticles at concentration of 1 wt-% and flow rates between 0 and 17 mL-min\({}^{-1}\). For comparison, also off-line DLS measurements on non-moving dispersions were performed using a state-of-art DLS instrument (Figure 4, green triangles). For that purpose, samples were taken during the reaction. Furthermore, samples were taken for TEM analysis, and immediately dried on a TEM grid after which the samples were analyzed (Figure 4, red squares). The deviation in particle size obtained using DLS between the off-line measured samples and the samples measured in flow is maximum 7%. This small deviation in particle size measured with conventional DLS on non-moving dispersions and in flow with the 3D cross correlation geometry DLS during synthesis of silica nanoparticles demonstrates that particle growth can be accurately monitored in real-time using our newly developed flow cell coupled DLS setup connected to the reactor using the analysis loop. The solvodynamic radius of the particles during synthesis, obtained through DLS, was compared to particle size obtained using transmission electron microscopy (Figure 4, red squares, Figure 5). Figure 4: Measurements during the synthesis process of (**a**) large silica particles; (**b**) small silica particles; the black dots represent real-time 3D cross correlation DLS measurements in flow (Q = 12.9 mL\(\cdot\)min\({}^{-1}\)), the green triangles represent conventional DLS measurements on the respective non-moving dispersions and the red squares represent TEM measurements (solid concentrations of silica dispersions of ca. 2.25 wt-%). Figure 5: _Cont._  
The average particle size obtained through TEM analyses was determined through measurement of at least 25 particles per samples. The particle sizes obtained using TEM analyses were smaller than those obtained using DLS. This can be explained by the fact that through DLS the solvodynamic radius of the particle is measured, and through TEM the radius of the dry particles [19]. For the large silica particles, the radii determined through TEM were approximately 10% smaller than those obtained through DLS. For the small silica particles, this difference was significantly larger, due the strong deviation of these particles from ideal spheres (Figure 5b). In contrast to the DLS techniques presented in this article, however, TEM not only provides information on the particle size but also on its shape and architecture. In addition to size, these are also important characteristics that influence the particle's property.