Drop-on-Demand Characterization and Shape Memory Performance of UV-Curable Shape Memory Polymers for Four-Dimensional Printing

Abstract

The current study investigated the inkjet printability and shape memory performance of shape memory polymers prepared from commercially available ultraviolet light curable polymers named Vero PureWhite (RGD837) and Agilus30 (FLX985) for four-dimensional (4-D) printing. The rheological properties of the samples, such as density, dynamic viscosity, and surface tension, were measured to calculate the dimensionless number “Z.” The value of “Z” calculated for all the samples was within the typical inkjet printability value of 1 < Z < 10. From the calculated dimensionless numbers, the Weber number (We) should be greater than 4 for droplets to be generated. Satellite formation with the main droplet was observed for Samples S3 (0.5 RGD837 + 0.5 FLX985), S4 (0.9 RGD837 + 0.1 FLX985), and S5 (0.3 RGD837 + 0.7 FLX985) in the numerical simulation. However, as the main drop progressed further, the satellite drops coalesced with the main droplet, resulting in a single stable droplet. The developed numerical model using the level set method supports the validation of drop characteristics prior to experimentation with various inkjet nozzles. Further, the numerical model was validated with an experimental study by ejecting the inks through a 0.1 mm diameter nozzle using a 27 mm piezo disk. Sample strips printed using the prepared inks demonstrated complete shape recovery at ∼45°C in bridge and cantilever mode at 9 and 7 s, respectively, with a shape recovery ratio of 99.4 %. The investigation validated that it is possible to inkjet 4-D print with the prepared shape memory polymers because 4-D printing that uses the inkjet method demands inks with highly controlled rheological properties. The properties in achieving the drop-on-demand performance of an ink such as diameter, velocity, and volume exhibited good correlation, indicating that the drop-on-demand performance of a polymer ink can be validated numerically, along with the printability diagrams.