Evaporation is the process where molecules transition from a liquid phase into a gas or vapor phase below the boiling temperature. Every liquid, including oils, possesses a measurable tendency to evaporate. For coconut oil, however, the rate of this process at room temperature is so slow that it is practically negligible compared to volatile liquids like water or alcohol. This difference is due to the substance’s underlying physical chemistry, which governs how easily its molecules can escape the liquid surface.
The Science of Evaporation
Evaporation occurs when molecules at the liquid surface gain enough kinetic energy to overcome the attractive forces holding them to the rest of the liquid. Because molecules possess a wide distribution of kinetic energies, some fast-moving molecules always reach the surface with sufficient energy to escape into the air. The tendency of a liquid to change into a gas is quantified by its vapor pressure. A higher vapor pressure at a given temperature indicates a higher rate of evaporation, meaning the liquid is more volatile.
Stronger intermolecular forces require more energy for molecules to escape, resulting in a lower vapor pressure and a slower evaporation rate. Temperature directly affects this dynamic because increasing the heat increases the average kinetic energy of the molecules, accelerating the rate of transition into the gas phase. The boiling point is reached when the liquid’s vapor pressure equals the surrounding atmospheric pressure.
Coconut Oil’s Chemical Structure
Coconut oil is classified as a triglyceride, consisting of a glycerol backbone attached to three fatty acid chains. The oil is dominated by saturated fatty acids, primarily lauric acid, which makes up about 44% to 49% of the oil’s total composition. These long, complex chains give the triglyceride molecule a high molecular weight, typically averaging between 640 and 680 grams per mole.
The size and complexity of these molecules lead to strong intermolecular forces between neighboring oil molecules, primarily London dispersion forces. These forces are much more powerful than attractions found in volatile compounds, requiring substantial thermal energy to overcome them. Consequently, few molecules gain enough kinetic energy to break free from the liquid surface and transition into the gas phase at room temperature.
This structural resistance results in extremely low volatility for coconut oil. The boiling point is estimated to be around 450 degrees Celsius, compared to water’s 100 degrees Celsius. This massive energy difference explains its minimal vapor pressure and why the oil does not visibly diminish or evaporate under normal ambient conditions.
Practical Implications of Low Volatility
The low volatility of coconut oil has several observable consequences in everyday use. Since the oil does not readily turn into a gas, any amount left on a surface remains as a residue, rather than dissipating like a solvent. This characteristic is beneficial for its stability, making it highly resistant to oxidation and rancidity.
This inherent stability allows coconut oil to maintain a long shelf life, often lasting for years without significant degradation. The oil’s reluctance to turn into vapor makes it a widely used carrier oil in cosmetic and skincare applications. When applied to the skin, it forms a lasting protective layer that remains in place, unlike lighter, more volatile cosmetic ingredients. This low volatility ensures the oil stays on the skin to deliver moisture and act as an effective emollient.
Vegetable oils, including coconut oil, are explored for use as industrial lubricants due to their low volatility and good temperature-viscous properties. A common point of confusion is the “smoke point” observed during cooking. When coconut oil reaches its smoke point (around 177 degrees Celsius for unrefined oil), the visible vapor is not the oil evaporating. Instead, intense heat causes the triglycerides to chemically decompose into smaller, more volatile compounds like free fatty acids, which then vaporize and produce the smoke.