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The Impact of Continuous Oxygen Flux in a Thin Film Photopolymerization Reaction with Peroxy‐Mediated Regeneration of Initiator
Author(s) -
Wong Jisam,
Sikes Hadley D.
Publication year - 2016
Publication title -
macromolecular theory and simulations
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.37
H-Index - 56
eISSN - 1521-3919
pISSN - 1022-1344
DOI - 10.1002/mats.201500098
Subject(s) - eosin , eosin y , photopolymer , chemistry , oxygen , photochemistry , diffusion , oxidizing agent , polymerization , kinetics , chemical engineering , catalysis , polymer , organic chemistry , medicine , staining , physics , pathology , photocatalysis , quantum mechanics , engineering , thermodynamics
Eosin, a photosensitizer dye that can exist in multiple oxidation states, has been shown to initiate visible‐light photopolymerizations of acrylates in open air when used in combination with tertiary amines. The exact mechanism behind this reactivity with micromolar concentrations of eosin in aqueous monomer solutions initially containing millimolar concentrations of oxygen has not been conclusively established, although pathways for regeneration of eosin in the presence of oxygen certainly play a role. In this work, a reaction–diffusion model incorporating a peroxy‐mediated eosin‐regeneration mechanism is built to explore the effects of oxygen diffusing into the system as the light‐activated reaction proceeds. An oxygen concentration‐dependent flux boundary condition is used to model the continuous replenishment of oxygen at the surface open to air as it is consumed by reaction. The model predicts the formation of a free radical concentration front that initially forms closer to the open surface and gradually moves toward the closed surface, with polymer film thickness increasing and the time required for polymerization to begin decreasing as the initial eosin concentration is increased. These results suggest that oxygen's dual role as both a free radical inhibitor and a precursor of the oxidizing species required for regeneration of eosin brings about interesting spatial variations when the reaction is carried out in a thin film geometry that is exposed to open air. In this case, an assumption of a well‐mixed system is not appropriate and the kinetics of the reaction and conversion as a function of position are likely to depend on the geometry of the system.