A recent study from Saarland University is proposing a new explanation for why ice is slippery, challenging a theory that has been widely accepted for nearly two centuries. The research, led by Professor Martin Müser and his colleagues Achraf Atila and Sergey Sukhomlinov, suggests that the interaction between molecular dipoles in ice and those in contacting materials is the primary cause of slipperiness, rather than the traditional explanation of pressure and friction causing melting.
The long-standing theory, first proposed by James Thomson, brother of Lord Kelvin, almost 200 years ago, posited that pressure and friction, combined with temperature, were responsible for melting ice and creating a lubricating liquid layer. However, the new findings, published in the journal Physical Review Letters, indicate that molecular dipoles are the key agents. When an object, such as a shoe or ski, contacts ice, the dipoles within the contacting material disrupt the ice's ordered crystalline structure, leading to a disordered, liquid-like film at the interface.
Professor Müser stated, "It turns out that neither pressure nor friction plays a particularly significant part in forming the thin liquid layer on ice." This discovery suggests that the material properties of the contacting surface play a crucial role in how slippery ice feels. For instance, hydrophobic surfaces, which repel water, are found to reduce friction more effectively than hydrophilic ones.
The implications of this research extend beyond everyday winter experiences. It offers a deeper understanding of material deformation and friction at the molecular scale, which could lead to the development of advanced materials and surfaces engineered to be less susceptible to ice adhesion. This could improve safety and performance in various applications, from winter sports equipment to transportation infrastructure.
Furthermore, the study addresses the behavior of ice at extremely low temperatures. While older theories suggested that skiing below -40°C would be impossible due to the lack of a lubricating film, the new findings indicate that dipole interactions persist even near absolute zero. However, the resulting liquid film becomes highly viscous, akin to honey, making activities like skiing or skating impractical, though the phenomenon of a liquid-like layer still exists.