ERI: Understanding the Dynamic and Thermal Behaviors of Colloidal Droplets Toward a Novel Freezing-based Inkjet Printing Concept

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This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).Inkjet-based additive manufacturing technology has been widely used for manufacturing complex and advanced structures. Conventional inkjet 3D printing creates layer-by-layer structures by jetting colloidal droplets onto a substrate with subsequent evaporation and deposition. While this inkjet technology can provide fast and efficient non-contact manufacturing with additional design and material flexibilities, it suffers from drawbacks such as coarse resolution, lack of adhesion, manufacturing inconsistency, and uncertainty in mechanical properties of printed parts. These undesired effects arise from droplet placement errors, uncertainty in droplet spreading, and uneven deposit distribution, due to the liquid nature of the colloidal droplets. To overcome these disadvantages, this work proposes a novel freezing-based inkjet printing concept that freezes the colloidal droplets upon impact followed by sublimation, eliminating the undesirable overspreading, particle transport, and fluid motions during deposition. The project aims to provide a better understanding of the fundamental physical details of the dynamic and thermal behaviors of colloidal droplets during the impact, deformation, and freezing processes, which govern the deposit resolution and uniformity of the freezing-based inkjet process. The knowledge developed has potential applications in the aerospace, healthcare, biomedical, and automotive industries. The project will also provide a wide range of educational and outreach activities, including a multi-year graduate/undergraduate research program, development of new teaching modules, and an outreach program for local K-12 students, especially those from groups underrepresented in STEM fields.The proposed research seeks to advance the fundamental understanding of the dynamic and thermal behaviors of colloidal droplets in the novel freezing-based inkjet 3D printing process. The proposal envisions three major foci: (i) quantitatively characterize the dynamic behaviors and thermal evolutions of colloidal droplets during impact, deformation, and freezing/solidification processes under different ambient and surface conditions; (ii) extract the associated dynamic and thermal time scales; and (iii) examine the deposit morphologies with varying ambient temperature, humidity, surface temperature, and hydrophobicity. This project will establish the foundation for a long-term research program focused on the development of the novel freezing-based inkjet 3D printing technique tailored for fabricating high-quality functional structures in various applications.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.