# Thermomechanics of Picoliter Liquids Encapsulated in Metal Microarchitectures

## TL;DR

This paper introduces a new method to encapsulate tiny amounts of liquid in copper structures and study their mechanical behavior at extreme temperatures.

## Contribution

A novel single-step method for encapsulating picoliter liquids in metal microarchitectures and testing their mechanical properties under extreme conditions.

## Key findings

- Encapsulated liquid is incompressible at room temperature but enhances load-bearing at -160°C as ice.
- Copper-ice composites show improved strength and energy dissipation due to ice's size-dependent strength.
- The method allows direct mechanical testing of liquids and ice at the microscale.

## Abstract

Probing the mechanical behavior of liquids at the nanoscale—especially under hydrostatic stress with various strain rates and extreme temperature conditions—holds significant potential for advancing microfluidic, biomedical, and energy systems. However, it remains experimentally challenging due to the inherent difficulties in encapsulation of liquid at micro/nanoscale and in accurately applying and measuring stress within confined microscale environments. In this work, we present a novel single‐step method for liquid encapsulation at the microscale and subsequent in situ micromechanical testing at extreme dynamic thermomechanical conditions. Localized electrodeposition in the liquid process enables the direct formation of hollow copper microarchitectures containing picoliters of liquid. The presence of the encapsulated liquid was verified via structural analysis at cryogenic and elevated temperatures. We investigated the mechanical role of the confined liquid through compressive tests, demonstrating its incompressibility at room temperature and its enhanced load‐bearing capacity in the ice phase at −160°C. These results reveal enhanced energy dissipation due to the size‐dependent strength of ice. Additionally, we evaluated the tensile response of copper‐ice composites at −160°C using microfabricated push‐to‐pull structures. Our findings outline a new pathway for encapsulation of liquids in metal microarchitectures that could aid and impact fields of microelectronics, pharmaceuticals, and energy storage.

Picoliter‐scale water is encapsulated inside hollow copper microcylinders through a single‐step localized electrodeposition process. Mechanical testing at room and cryogenic temperatures reveals that incompressible liquid and load‐bearing microscale ice enhance the strength and deformation behavior of the composite structure. This work enables direct encapsulation of liquid/ice and probing of their mechanics at the microscale.