Spreading of fast-curing, thermosetting silicones

Abstract

This letter presents an experimental study and the associated numerical modeling of fast-curing, thermosetting droplets spreading on a heated surface. The results show a significant morphological dependence of the spreading droplets of Ecoflex 0050 (a heat-sensitive, platinum-catalyzed silicone material) on thermal conditions. Differential scanning calorimetry and rheometry provide quantifiable data for modeling the cure kinetics and rheological properties of the material. This work demonstrates an approach to developing a phenomenological model suitable for predicting the morphological variation of fast-curing, thermosetting materials without prior knowledge of their chemical composition. The developed multiphysics models for cure kinetics and chemorheology can serve as a functional tool for predictions requiring accurate dimensional control of free-forming thermosetting materials, such as nozzle-based additive manufacturing, centrifugal coating and forming, fabrication of soft robots, and soft lithography.

Predicting the Dynamics and Steady-State Shape of Cylindrical Newtonian Filaments on Solid Substrates

“…We have previously shown that the most appropriate condition is an equation relating the dynamic contact angle to the dimensionless contact line velocity, i.e., Ca. eq was shown to work extremely well at capturing the spreading of spherical droplets and is employed unchanged in this work. , n̅ · ( T̿ I − T̿ II ) = σ ( ∇̅ · n̅ false) n̅ − ∇̅ σ τ̅ normalf = μ u̅ β u̅ · n̅ wall = 0 c o s ( θ s ) − c o s ( θ D ) c o s ( θ s ) + 1 = t a n h ( A Ca B ) …”

“…We have previously shown that the most appropriate condition is an equation relating the dynamic contact angle to the dimensionless contact line velocity, i.e., Ca. eq was shown to work extremely well at capturing the spreading of spherical droplets and is employed unchanged in this work. , …”

“…One reason for this is the infinite interfacial instability of deposited filaments, which causes them to break up into spherical beads over time . Despite this limitation, cylindrical filaments have become a useful method of 3D printing, whereby the instability is prevented via stabilizing elastic stresses induced by reacting a thermoset resin to form a gel network, ,, or through rheological modifiers that thicken after deposition. ,− In this study, we present a general theory for the spreading of cylindrical filaments on solid substrates that considers Newtonian fluids with varying effects of gravity and static advancing contact angles. Although this theory does not currently account for the evolution of elastic stresses, it provides a baseline or upper bound for the spreading that would be observed experimentally in 3D printing methods.…”