Non-surface-active refers to substances that do not significantly alter the interfacial tension between two phases, typically a liquid and a gas, or two immiscible liquids. Unlike surfactants, these compounds do not tend to concentrate at interfaces, and therefore do not exhibit properties such as emulsification, detergency, or foaming. They maintain bulk properties within the continuous phase and do not have pronounced effects on the surface tension. They act only at the bulk and will not effect interfaces. They can also be described as compounds that are not amphiphilic in nature. Amphiphilic compounds consist of both hydrophilic (water-loving) and hydrophobic (water-fearing) components that concentrate at the interface.
Non-surface-active meaning with examples
- Consider a sugar solution; sucrose molecules, acting as non-surface-active agents, dissolve uniformly, influencing bulk properties like sweetness and viscosity, but not the surface tension of the liquid. They will not form micelles, and do not aid in dispersing oil in water. Their interaction is solely within the aqueous bulk.
- In contrast to a detergent, a saturated alcohol like ethanol, as a non-surface-active solvent, functions mainly to dissolve a given compound within a liquid and has no specific effect on surface tension, thus not aiding in removing grease or dirt from a surface. It does not work in the same fashion.
- Many salts are considered non-surface-active. For example, dissolved sodium chloride. These compounds will alter the bulk properties of water such as salinity but would not concentrate at air-water or oil-water interfaces or lead to micelle formation and have no impact on foaming capacity.
- Glycerol functions as a humectant because it is non-surface-active. It draws moisture into the liquid phase without affecting the interfacial properties. It influences bulk viscosity, and water absorption, but does not accumulate at the interface, maintaining the continuous nature of the system.