Nobody likes to swim in cold water but heating a pool is expensive. Solar blankets can help, but it’s a pain to drag them on and off. But how about a liquid pool cover? Believe it or not, that‘s a possibility! Just throw a plastic dispenser of stearyl alcohol into the water, usually in the shape of a fish, and you can cut down on heat loss. The stearyl alcohol, released at a controlled rate by a microprocessor in the dispenser, rises to the surface of the water where it forms a layer that is only one molecule thick, known as a “monolayer.” This acts as a sort of lid on the water and keeps it from evaporating. And evaporation leads to heat loss, as anyone who has spilled alcohol or acetone on their hand can testify. It takes energy to convert a liquid to a gas, and that energy is drawn from the surroundings. When water evaporates from the surface of a pool, the remaining water loses heat. Since the monolayer of stearyl alcohol retards evaporation, it helps to keep the water from losing heat. But don’t expect to convert a pool into a hot tub. Remember that stearyl alcohol does not heat the pool, it only slows the rate of cooling.
Of course any time a chemical is added to the water in a pool, safety issues have to be considered. Stearyl alcohol is in fact so safe that it is sometimes even added to drinking water reservoirs to slow the loss of water to the atmosphere. It is also widely used in cosmetic creams and lotions at concentrations way above that found in swimming pool water without any safety problems. Here it acts as an emulsifier and emollient. Emulsifiers are molecules that have one water soluble end and one oil soluble end and allow oily compounds to mix with water. That is exactly what is needed to formulate a cream or lotion.
Emollients on the other hand soften the skin by preventing moisture loss. In this case stearyl alcohol performs the same job as in a pool. It accumulates in the top layer of the skin and keeps moisture from evaporating. Some people avoid skin care products that contain alcohol because they worry about a drying effect. That is a legitimate concern with ethanol and isopropanol, because these are small molecules that readily evaporate from the surface of the skin and actually encourage water evaporation. Such is not the case with the so called “fatty alcohols” like stearyl or cetyl alcohol. These large molecules that do not evaporate readily. The reason they’re called fatty alcohols is because they are produced from fats. Stearic acid, for example, is readily prepared by heating animal or vegetable fats under alkaline or acidic conditions. It can then be converted to stearyl alcohol by catalytic hydrogenation, ready to be dispensed from a plastic fish to improve the comfort of your swim, or from a bottle or jar to make your skin feel nice and smooth after that swim.