Slippery Secrets of an Icy Road

20.02.2024

Table of Contents

Introduction

Once again, with temperatures dropping and substantial snowfall, Christmas plans are at the mercy of winter’s icy influence, coinciding with one of the United States’ busiest travel weeks. The frigid conditions result in perilously slippery roads and frequent flight delays, requiring extensive de-icing measures. But what factors determine whether ice adheres or slides on surfaces? Reporting in Materials Horizons journal, a multi-institutional study from University of Illinois Chicago and Argonne National Laboratory takes the cold plunge into unraveling the many mysteries of ice.

The eternal quest for icephobicity

Accumulation of ice on engineering surfaces such as aircraft, wind turbines, marine vessels, power transmission lines, or heat exchangers poses a significant threat to their operational safety and structural integrity. To counter the damage caused by ice buildup, extensive research has focused on developing surfaces that minimize ice accretion and/or interfacial adhesion. However, the majority of these investigations have primarily addressed freshwater ice adhesion. Yet, the freezing of water on surfaces reveals a complex environment with a myriad of impurities. Surface treatments that could diminish the adhesion of impure ice could offer substantial benefits, yet there is limited understanding of how contaminated ice adheres to surfaces.

Adhesion of impure ice on surfaces

Examining freezing water solutions representative of natural water bodies, we investigated how ice adhesion is affected by varying concentrations of impurities (salt, surfactant, and alcohol) on standard industrial surfaces (copper, glass, and silicon) at sub-zero temperatures. Utilizing X-ray microcomputed tomography and molecular dynamics simulations, we explored the impact of salt concentration and substrate subcooling on ice adhesion, revealing alterations in ice pocket geometry and quasi liquid layer thickness. The study also delved into how the freezing rate influences impurity entrapment, potentially contributing to the elevated ice adhesion strength observed in Arctic climates on marine vessels.

Key findings

• This research uncovers how impurities in water alter the freezing process on solid surfaces, causing changes in the adhesion strength of impure ice.

• Through experiments with varying impurity concentrations, we identified threshold levels for adhesive failure across different impurity species and base substrates.

• A decrease in ice adhesion strength was observed on moderately chilled surfaces, regardless of impurity type, even with minimal impurity amounts in the ice, despite the hydrophilic nature of the underlying surfaces.

• Depending on the freezing rate and surface temperature, impurities may either become trapped within the ice or be displaced along the freezing front, leading to the formation of a non-freezing lubricating layer and contributing to low adhesion strength in impure ice.

• Molecular dynamics simulations concurrently revealed that the presence of contaminants dynamically alters interactions within the disordered liquid layer between impure ice and the solid surface, potentially impacting ice adhesion strength.

Interpretation

The research demonstrates that ice can become slippery with impurity-laden solutions, eliminating the necessity to alter surface texture or material chemistry for ice-shedding applications. This opens up design possibilities for coatings releasing contaminants, altering interfacial adhesion across applications with varying adhesion strength requirements.

Conclusion

The findings provide comprehensive insights into how impurities affect ice adhesion, with wide-ranging implications. This spans from reconsidering the current framework for measuring surface ice repellency to understanding glacier movements and developing freeze-protection technologies for industrial use.

Exploring how various contaminants, either alone or in combinations, impact the adhesion of intricate ice structures to solid surfaces is vital for unlocking the next phase of innovation in icephobicity.