Variable temperature multiple light scattering analysis to determine the enthalpic term of a reversible agglomeration in submicrometric colloidal formulations: A quick quantitative comparison of the relative physical stability

In this work, we propose the variable temperature multiple light scattering (VTMLS) as a novel method to determine an enthalpic term of the agglomeration process of submicrometric colloidal systems such as polymeric nanocapsules (NCs) and lipid-core nanocapsules (LNCs). Four different aqueous suspensions were prepared using a linear polyester, triacylglycerol, octyl methoxycinnamate and polysorbate 80 in the presence (individually and combined) or absence of the surfactants: phosphatidylcholine and sorbitan monostearate. Backscattering (BS) signals were monitored applying a temperature gradient from 23 °C to 56 °C (increase of 3 °C at 5-min intervals). Considering the Indefinite Self-Association Model, a relation between the BS signal and the equilibrium constant of the agglomeration process was established. The values of A′ΔH°, obtained by VTMLS for each colloidal aqueous suspension, were predictive of the system physical stability when compared to long-term stability studies. The use of phosphatidylcholine decreased the physical stability of either LNC or NC. The approach enabled to differentiate the first step of the physical destabilization, which corresponds to a reversible surfactant desorption. In conclusion, the new non-destructive analysis can be used to quickly compare the relative physical stability of colloidal systems representing a valuable tool to develop new formulations of dispersed systems.