Unlike water, which forms crystalline structures, most oils only become more viscous and thick.
Water famously solidifies at 0°C, forming ordered crystalline ice structures. But what about oil, whether in your kitchen or in your car engine? As temperatures drop, the Oils behave very differently of water and understanding why reveals a lot about its molecular composition.
Freezing, in scientific terms, occurs when a liquid loses heat to the environment and turns into solid. In water, this process is well understood: its angular molecules come together in hexagon-shaped clusters, creating the familiar crystalline patterns found in ice. “When water freezes, its molecules begin to group together,” explains Maxim Lavrentovich, assistant professor of Theoretical Biophysics at the University of Tennessee. The uniform structure of water molecules makes this well-defined freezing point possible.
Oils, however, are another story. Unlike water, oils are nonpolar and hydrophobic, consisting of long chain lipid molecules of varying lengths and shapes. This structural diversity prevents them from forming the organized and perfect crystals characteristic of frozen water. According to Ask The Physics Van at the University of Illinois, the irregular shapes of these lipid molecules “make it difficult for regular crystals to form in the oil, suppressing common freezing.”
This does not mean that oils are not affected by the cold. As temperatures drop, oils become increasingly viscousvisibly thickening. However, they do not solidify at a single, well-defined freezing point, as water does. Instead, its molecules slowly lose energy and mobility, causing the substance to gradually harden. In this sense, oils can be considered “frozen” when they reach a state close to solid, but without forming the crystalline structures that define true crystalline solids, says .
There are exceptions within the broad category of oils. Cocoa butter, for example, can crystallize and solidify at around 34°C, thanks to its more uniform molecular composition. But for most common oils, from vegetable oils to automotive lubricants, cooling results in thickening, not a precise phase change.
This behavior has practical implications, especially in machines and automobiles. Engine oil does not freeze into a rigid block, but low temperatures drastically increase its viscosity, which can make it difficult to pump oil for critical engine components. This delay reduces lubrication during engine start-up, a critical time when parts depend on immediate oil flow.
Ultimately, while the water turns from liquid to ice cleanly, the oils enter a slow, semi-solid statewithout ever forming crystalline structures. Their complex molecular composition makes them resistant to complete freezing — an advantage in many situations, but still requires caution when temperatures drop drastically.
