Session: 16-01-01: Government Agency Student Poster Competition

Paper Number: 150092

150092 - Designing Liquid Metal Microstructures From Spherical to Ellipsoidal Inclusions via Direct Ink Writing 

Soft, elastically deformable composites based on liquid metal can enable new generations of multifunctional materials for electronics, robotics, and reconfigurable structures. Controlling liquid metal (LM) droplet microstructure within these composites through direct ink write (DIW) printing holds significant promise to tailor and greatly enhance material properties. This research aims to systematically optimize DIW printing parameters and rheological properties of LM ink to control the microstructure of LM droplets, transforming them from nearly spherical shapes to highly elongated ellipsoidal forms. By understanding the interplay between rheological properties such as ink viscosity (η), LM droplet size (D) and printing parameters such as print height (H) and relative velocity (V* = V/C) between print head velocity (V) and extrusion rate (C), we establish guidelines for programming the microstructure of LM-polymer composites during the DIW process.

Experimental investigations revealed that rheological properties of LM ink, along with process parameters such as H and V* can significantly influence LM microstructure. By tuning these parameters, nearly spherical LM droplets were transformed into ellipsoidal shapes with an average aspect ratio of 12.4. An ink viscosity threshold was identified as essential for successful reconfiguration, while the presence of a thin oxide layer on LM droplets played a critical role in maintaining the elongated shape. These insights led to the development of quantitative design maps, offering a framework for optimizing material and process parameters during DIW printing process.

With this foundational knowledge, the application of anisotropic and heterogeneous structures for directing heat dissipation in LM soft composites (LMSC) was explored. The DIW process enabled the creation of LMSCs with varied (spherical and elongated) and directional (anisotropic) microstructures using a single LM ink. The study demonstrated that the thermal conductivity of the composites is highly dependent on the microstructure of LM droplets, particularly the intensity and orientation of elongation. By achieving an elongated LM microstructure, the thermal conductivity in the direction of elongation (k_y) reached 9.9 W/m·K, a notable increase compared to the unfilled elastomer (0.24 W/m·K). This enhanced thermal conductivity underscores the potential of LM microstructure optimization in efficient thermal management systems.

Furthermore, the DIW printing process allowed for the orientation of LM droplets in different directions and control over the degree of elongation at various locations within the composite. This capability facilitated the fabrication of anisotropic and heterogeneous paths that direct and control heat transfer within a single continuous LMSC without the need for additional processing steps. Such advancements provide a novel approach to achieving high thermal conductivity through designed LM microstructures, addressing the challenges posed by the increasing complexity and miniaturization of soft electronic devices.

In conclusion, this research provides a  thorough understanding of how to optimize DIW printing parameters and LM ink properties to achieve elongated LM droplet microstructures. These optimized structures significantly enhance thermal properties of LM soft composites. The methodologies and design maps developed herein serve as valuable tools for future innovations in additive manufacturing and thermal management technologies, paving the way for advanced multifunctional materials with tailored properties.

Presenting Author: Ohnyoung Hur Virginia Tech

Presenting Author Biography: I am currently a third-year PhD student in Dr. Bartlett's Soft Materials and Structures Lab. My research focuses on 1) designing liquid metal (LM) droplets through Direct Ink Write (DIW) 3D printing by tuning rheological properties and optimizing printing conditions, 2) developing highly thermally conductive composites through DIW 3D printing, and 3) understanding the mechanical properties of LM composites with anisotropic LM microstructures designed through DIW 3D printing. Ultimately, I want to develop soft electronics based on liquid metal based composite.

Authors:

Ohnyoung Hur Virginia Tech
Ravi Tutika Virginia tech
Eric Markvicka University of Nebraska–Lincoln
Michael Bartlett Virginia Tech