1 Full Paper Macromolecular Chemistry and Physics wileyonlinelibrary.com DOI: 10.1002/macp.201400072 Absorption and Scattering in Concentrated Monomer Miniemulsions: Static and Dynamic Investigations Emeline Lobry, Florent Jasinski, Marta Penconi, Abraham Chemtob,* Christian Ley, Céline Croutxé-Barghorn, Esther Oliveros, André M. Braun, Adrien Criqui Low-scattering monomer miniemulsions have recently emerged as a suitable system for the development of efficient 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 find 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-flux theory of Kubelka–Munk on these multiple scattering miniemulsions enables the determination of the scattering and absorption coefficients for different initial droplet sizes. These results show that reaction kinetics are strongly correlated with scat- tering efficiency. Below a threshold average diameter of ca. 150 nm, any decrease of droplet size diminishes the extent of scattering significantly, 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. E. Lobry, F. Jasinski, Dr. A. Chemtob, C. Ley, C. Croutxé-Barghorn Laboratory of Photochemistry and Macromolecular Engineering, ENSCMu, University of Haute Alsace, 3 Rue Alfred Werner, 68093 Mulhouse Cedex, France E-mail: abraham.chemtob@uha.fr M. Penconi, E. Oliveros Laboratoire des IMRCP, UMR CNRS 5623, Université Toulouse III (Paul Sabatier, UPS), 118, Route de Narbonne, 31062, Toulouse Cedex 9, France A.-M. Braun Engler-Bunte-Institute, Karlsruhe Institute of Technology (KIT) 76131 Karlsruhe, Germany A. Criqui Mäder Research MADER GROUP, 130 Rue de la Mer Rouge, 68200 Mulhouse, France 1. Introduction In emulsion-polymerization processes, the most widely used methods for the generation of radicals are thermal decomposition of initiators (peroxide, azo compounds) and redox systems. Extension to photoinitiators (PIs) able to produce radicals upon UV or visible light irra- diation is in itself a challenge. [1–4] Nonetheless, there are strong incentives to develop efficient photochemical means of producing polymer particles in water. Photoini- tiation is the fastest process for the creation of primary radicals, while requiring the lowest activation energy. A broad range of PIs – although initially developed for UV-curing purposes – are commercially available with Early View Publication; these are NOT the final page numbers, use DOI for citation !! Macromol. Chem. Phys. 2014, DOI: 10.1002/macp.201400072 © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim