Absorption and Scattering in Concentrated Monomer Miniemulsions: Static and Dynamic Investigations

Low-scattering monomer miniemulsions have recently emerged as a suitable system for the development of effi cient photopolymerization processes in dispersed media. Since their reac-tivity under UV exposure is strongly dependent on their optical properties, there is a strong interest to fi nd simple analytical methods for studying absorption and scattering with ready-to-polymerize concentrated miniemulsions, while avoiding dilution. This paper focuses on three types of concentrated miniemulsions without photoinitiator (PI) and containing either a hydrophilic or hydrophobic PI. The application of the two-fl ux theory of Kubelka–Munk on these multiple scattering miniemulsions enables the determination of the scattering and absorption coeffi cients for different initial droplet sizes. These results show that reaction kinetics are strongly correlated with scat-tering effi ciency. Below a threshold average diameter of ca. 150 nm, any decrease of droplet size diminishes the extent of scattering signifi cantly, thus improving light penetration and the reaction rate. Additionally, a complementary dynamic study proves that the smallest miniemulsions are subjected to a decrease of scattering during irradiation. This result opens up interesting perspectives on the elucidation of the nucleation mechanism operating in a miniemulsion photopolymerization.