Abstract
Frontal photopolymerization (FPP) is a rapid and versatile solidification process that can be used to fabricate complex three-dimensional structures by selectively exposing a photosensitive monomer-rich bath to light. A characteristic feature of FPP is the appearance of a sharp polymerization front that propagates into the bath as a planar traveling wave. In this paper, we introduce a theoretical model to determine how heat generation during photopolymerization influences the kinetics of wave propagation as well as the monomer-to-polymer conversion profile, both of which are relevant for FPP applications and experimentally measurable. When thermal diffusion is sufficiently fast relative to the rate of polymerization, the system evolves as if it were isothermal. However, when thermal diffusion is slow, a thermal wavefront develops and propagates at the same rate as the polymerization front. This leads to an accumulation of heat behind the polymerization front which can result in a significant sharpening of the conversion profile and acceleration of the growth of the solid. Our results also suggest that a novel way to tailor the dynamics of FPP is by imposing a temperature gradient along the growth direction.
Highlights
Photopolymerization is a robust solidification process that takes place when a photosensitive monomer-rich bath is exposed to light
The remainder of this paper will focus on extending the model in Eq (1) to include thermal effects in order to examine how these influence the dynamics of Frontal photopolymerization (FPP), the width of the interfacial layer, w, and the motion of the sharp solidliquid interface, zf
We find that the temperature influences the dynamics of FPP in similar ways regardless of the relative size of the attenuation coefficients
Summary
Photopolymerization is a robust solidification process that takes place when a photosensitive monomer-rich bath is exposed to light. In one group are physicochemical models that accurately account for each of the reaction steps, e.g., photolysis, photoinitiation, propagation, chain transfer, and termination [31,32,33,34]; oxygen inhibition [35,36]; nonuniform distributions in the length of polymer chains [37,38]; heat generation and transport [20]; mass transport due to convection and/or diffusion [25,39]; and optical effects such as scattering [40] and refractive index modulation [41] Such models can offer theoretical insights into photopolymerization processes, their practical use is limited by a lack of tractability and large number of parameters, some of which cannot be measured experimentally.
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