New experiments show that small water droplets can remain liquid at minus 44 degrees Celsius

One of the things we learned in the elementary school classroom is that water freezes at 0°C (32°F). But in the field of scientific research, it is actually not so simple. New experiments at the University of Houston show that small water droplets can remain liquid at -44°C (-47.2°F) if kept in contact with a soft surface.

The freezing point of water is not a hard boundary — it is more like a starting point where water molecules begin to freeze. The first to convert are those water molecules exposed to the cold air on the surface, and the ice crystals they form cause neighboring molecules to freeze as well. This process continues until the entire body of water turns to ice.

For any given water droplet, it will start freezing between 0°C and -38°C (-36.4°F). But in the new study, the researchers managed to make some particularly tiny droplets of water retain their liquid form at temperatures of minus 44°C.

According to the team, the key is the type of surface the water touches. Ice crystals form easily on hard surfaces, but softer interfaces, such as oil or gel, can inhibit the formation of ice crystals for longer. Smaller water droplets can even hold the liquid longer than the larger water droplets.

To get a closer look at the physical process of the transition from water to ice, the team is experimenting with water droplets that are only two nanometers in diameter, and the usual range is about 100 nanometers. To do this, the researchers confined the water to the pores of a membrane made of anodized aluminum. Nano droplets are surrounded by octane oil to keep the interface "soft".

Hadi Ghasemi, corresponding author of the study, said: "Experimental detection of freezing point temperatures of several nanometer water droplets has always been an unresolved challenge. Through newly developed dosing methods, we have been able to detect the freezing of water droplets from the micron scale to the 2 nanometer scale."