**4.1 Average size and size distribution**

The average size and size distribution of submicron particles are usually measured by dynamic light scattering (DLS), which is based on the equivalent sphere principle

when an incident beam interacts with the sample particles. Well-prepared nanocapsule systems should be in the nanometer range and with a narrow particle size distribution. Therefore, numerous studies have paid attention to the effect of both the type and the concentration of the constituents, as well as the fabrication process variables, on the size and polydispersity index (PI) of the sample [44]. The disadvantage of DLS is that there are some parameters that may influence data, such as viscosity, pH, and temperature of the suspension medium, as well as concentration, colloidal instability, or the presence of aggregates [23]. On the other hand, microscopic methods are also used to determine nanocapsules' mean size, but they require the imaging of a large number of particles, and the measurement may be affected due to the sample dry state required for the analysis [24]. So, it is generally recommended to use at least two methods to determine the particle size and size distribution [23].
