Ionic liquids can be utilized in stereolithography (SLA) additive manufacturing resins to adjust multiple parameters of the resulting polymer, such as chemical stability, temperature stability, and other key physical properties. While studies into these properties are ongoing, little is known about the effects the presence of these ILs has on the polymerization process. This study intends to use a new technique incorporating acoustic levitation, FLIR thermography, and differential scanning calorimetry (DSC) to provide insight into heat of polymerization of the resins utilizing an approach previously developed in the Duranty laboratory. This technique allows a small amount of liquid to levitate in standing sound waves generated by transducers at the top and bottom of a 3D printed scaffolding. This novel approach maximizes the probability of heat transfer via convection (through the air/surrounding medium) while preventing heat transfer via conduction (through direct contact) that is normally observed in container methods, allowing for direct thermal imaging of the captured droplets. Two 405 nm lasers, mounted at the top and bottom of the apparatus, are utilized to mimic the lasers of SLA 3D printing which initiate the polymerization process. This apparatus allows for the direct observation of the temperature changes during the polymerization process.

A variety of ionic liquids were used in this investigation in order to study to effects of structure changes and ion effects. The study observed the effects of alkyl chain length, functional groups on the alkyl chain, anion effects, aromatic vs. non-aromatic, and potential co-polymer ionic liquids. Each ionic liquid was added to the commercial Clear V4 resin from Formlabs in the amount of 10 to 50 wt% ionic liquid. Once the mixtures were homogenous, 5 µL of each IL/resin mixture was suspended in the acoustic field. Thermographic data was collected before, during, and after the polymerization process which was initiated by exposure to 405 nm lasers. The heats of polymerization for each sample were calculated using heat capacity data collected via DSC along with the change in temperature of the droplet observed by FLIR thermographic imaging of the suspended droplet during polymerization. Thermal degradation temperatures of the resulting polymer matrices were determined via thermal gravimetric analysis (TGA). The combination of this data revealed that the addition of some of the ionic liquids targeted in this study reduced the heat of polymerization, while others increased it. Therefore, the cation and anion structures greatly impact the heat of polymerization.