We investigate the frontal photopolymerization
of a thiol–ene
system with a combination of experiments and modeling, focusing on
the interfacial conversion profile and its planar wave propagation.
We spatially resolve the solid-to-liquid front by FT-IR and AFM mechanical
measurements, supplemented by differential scanning calorimetry. A
simple coarse-grained model is found to describe remarkably well the
frontal kinetics and the sigmoidal interface, capturing the effects
of UV light exposure time (or dose) and temperature, as well as the
front position and resulting patterned dimensions after development.
Analytical solutions for the conversion profile enable the description
of all conditions with a single master curve in the moving frame of
the front position. Building on this understanding, we demonstrate
the design and fabrication of gradient polymer materials, with tunable
properties <i>along</i> the direction of illumination, which
can be coupled with lateral patterning by modulated illumination or
grayscale lithography