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Experimental Investigation of Room Temperature Liquid Metal Dynamic Behavior

  • Author(s): McGuan, Ryan
  • Advisor(s): Kavehpour, Hossein P
  • et al.

This dissertation consists of a focused study of the low melting point liquid metal known commercially as Galinstan. This metal is notable for being readily liquid at room temperature, being non-toxic, and forming a peculiar oxide layer that is confined to the surface of the liquid. This study consists of four parts. The first is a literature review of the field of flexible and stretchable electronics. The purpose of this review is to assess the state of the field and to make the case for the value of Galinstan as a primary conducting element in the manufacture of these devices. With this case made, the remaining three parts can be sorted into two overarching concepts: experiments designed to produce data relevant to the drop on demand printing of flexible electronics, and to the study of fundamental fluid mechanics phenomenon, often overlapping throughout.

The first study involves the use of tensiometry to measure the effective surface tension, as well as explore the wetting behavior of the liquid metal on glass. For measuring the surface tension, we developed a novel technique that combines principles of both the Wilhelmy plate method, but with a rod modification, with the Du No�y ring method. After measuring the surface tension, we studied the wetting behavior of the metal, namely the dynamic contact angle and found the advancing contact angle (θ??), receding contact angle (θ??), and the contact angle hysteresis θ??−θ??.

Next, we performed droplet impact experiments of liquid metal on glass substrate. Utilizing the wetting information from the tensiometry experiments, we were able to develop a novel model for impact driven spreading of liquid metal on glass for Weber numbers ranging from 10 to 205. This model shows new scaling behavior as compared to other droplet impact models and we compare and contrast these models of impact. This model is also predictive and would serve to modulate voxel size in additive manufacturing operations with Galinstan.

The final set of experiments were of partially coalescing liquid metal droplets in 1 M NaOH. These droplets were observed to bounce on the liquid metal interface and reach different heights as they coalesced into smaller and smaller droplets. We developed a first order model based on the Stokes approximation for droplets in a viscous fluid which we refined with a improved numerical model which was more valid for the range of Reynolds numbers tested.

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