What makes something hygroscopic

The total amount of water, which can be taken up by the hygroscopic material will be a function of the temperature and humidity of the atmosphere in which it is located and will ultimately be determined by the sorption isotherm of the system.

In general, the rate of transfer of moisture will fall off progressively as equilibrium is approached, not only because the concentration driving force becomes smaller, but also because the overall diffusional resistance to mass transfer increases as the more easily accessible elements of surface reach their equilibrium state so that, in a porous solid, the vapor must then diffuse into the more remote pores.

A particular example of hygroscopic behavior is deliquescence which is exhibited by many water-soluble solids, including inorganic salts e. At a given temperature, the vapor pressure of a saturated salt solution will be lower than that of pure water and, if it is less than the partial pressure in the atmosphere, moisture will be tranferred to the surface of the solids, part of which will dissolve to form a saturated solution.

When all the solids have dissolved, the process will continue until the partial pressure of the now unsaturated solution equals that in the atmosphere. In some cases, the formation of a hydrate or higher hydrate of the salt may precede the formation of a liquid phase. In contrast, when water vapor is adsorbed, the water molecules remain on the surface of the material.

You might encounter the word "hydroscopic" used in place of "hygroscopic," however, while hydro- is a prefix meaning water, the word "hydroscopic" is a misspelling and is incorrect.

A hydroscope is an instrument used to take deep-sea measurements. A device called a hygroscope in the s was an instrument used to measure humidity levels. The modern name for such a device is a hygrometer. Hygroscopic and deliquescent materials are both able to absorb moisture from the air. However, hygroscopy and deliquescence don't mean precisely the same thing: Hygroscopic materials absorb moisture, while deliquescent materials absorb moisture to the extent that the substance dissolves in water.

A hygroscopic material will become damp and may stick to itself or become caky, while a deliquescent material will liquefy. Deliquescence may be considered an extreme form of hygroscopy. While capillary action is another mechanism involving the uptake of water, it differs from hygroscopy in that no absorption occurs in the process. Hygroscopic chemicals require special care. Typically, they are stored in airtight containers. They may also be maintained under kerosene, oil, or within a dry atmosphere.

Hygroscopic substances are used to keep products dry or to remove water from an area. They are commonly used in desiccators. Hygroscopic materials may be added to products due to their ability to attract and hold moisture. These substances are referred to as humectants. Examples of humectants used in food, cosmetics, and drugs include salt, honey, ethanol, and sugar.

Hygroscopic and deliquescent materials and humectants are all able to absorb moisture from the air. Generally, deliquescent materials are used as desiccants. Their models could help researchers develop and test But a new study finds that water bears propel themselves through sediment and soil on eight stubby legs, in The researchers measured the spontaneous emission of fast Now they're building the hardware for Hidden Behavior of Supercapacitor Materials Nov.

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