Effects of Containerless Curing Through In Situ Characterization with Acoustic Levitation to Advance Manufacturing of Nanocomposites in Microgravity.

Acoustic levitation offers a microgravity-relevant platform for investigating the curing behavior of nanoparticle-filled photopolymers in a containerless environment. This is especially relevant for the design of in-space manufacturing methods to support space exploration. The objective of this work is to demonstrate a coupled in situ monitoring approach capable of capturing curing-induced structural changes and detecting differences in residual stress development between curing boundary conditions of microgravity relevance, specifically the presence or absence of container constraint, during Ultraviolet (UV) curing of a nanoparticle-filled photopolymer. In this work, an acoustic levitation system was integrated with a fiber optic-based in situ spectroscopy system in one setup and a synchrotron X-ray diffraction system in another to capture the structural and chemical changes during UV curing of nanoparticle photopolymers while monitoring nanocomposite bead shape and stability. The techniques yielded quantitative measurements of curing-induced peak shift, reflecting residual stress development, during the curing process in a containerless environment and surface-contacted environment with high temporal resolution. The results show that the contacted condition induces higher residual stress than the containerless condition throughout the curing process, from the liquid nanoparticle-polymer mixture to the final cured product. This difference highlights the influence of wall constraint on the curing as they relate to stress development during terrestrial processing. By comparing contacted and containerless curing, this ground-based characterization approach provides an accessible method for studying microgravity-relevant curing behavior and supports the development of processing strategies for reliable in-space manufacturing of polymer nanocomposites. Beyond this material system, this integrated approach can be applied to other materials for microgravity-relevant manufacturing.