Hygroscopic substances include sugar, honey, glycerol, ethanol, methanol, diesel fuel, sulfuric acid, methamphetamine, many salts (including table salt), and a huge variety of other substances.
Zinc chloride and calcium chloride, as well as potassium hydroxide and sodium hydroxide (and many different salts) are so hygroscopic that they readily dissolve in the water they absorb: this property is called deliquescence (see below). Sulfuric acid is not only hygroscopic in high concentrated form, its solutions are hygroscopic down to concentrations of 10 Vol-% or below. More commonly, a hygroscopic material will tend to become damp and "cake" when exposed to moist air (such as salt in salt shakers during humid weather).
Because of their affinity for atmospheric moisture, hygroscopic materials might necessitate being stored in sealed containers. When added to foods or other materials for the express purpose of maintaining moisture content, such substances are known as humectants.
Materials and compounds exhibit different hygroscopic properties, and this difference can lead to detrimental effects, such as stress concentration in composite materials. The amount a particular material or compound is affected by ambient moisture may be considered its coefficient of hygroscopic expansion (CHE) (also referred to as CME, coefficient of moisture expansion) or coefficient of hygroscopic contraction (CHC)—the difference between the two terms being a difference in sign convention and a difference in point of view as to whether the difference in moisture leads to contraction or expansion.
A common example where differences in hygroscopy can be seen is a plastic-laminated paperback book cover. Often, in a suddenly moist environment, the book cover will curl away from the rest of the book. The unlaminated side of the cover absorbs more moisture than the laminated side and increases in area, causing a stress that curls the cover toward the laminated side. This is similar to the function of a thermometer's bi-metallic strip. Inexpensive dial-type hygrometers make use of this principle using a coiled strip.
The similar-sounding but unrelated word hydroscopic is sometimes used in error for hygroscopic. A hydroscope is an optical device used for making observations deep under water.
Thorny devils collect moisture in the dry desert via night-time condensation of dew which forms on their skin and is channeled to their mouths in hygroscopic grooves between the spines of their skin. Water also collects in these grooves when it rains. Capillary action allows the lizard to suck in water from all over its body.
Other polymers, such as polyethylene and polystyrene, do not normally adsorb much moisture, but are able to carry significant moisture on their surface when exposed to liquid water.
Type-6 nylon can absorb up to 9.5% of its weight in moisture.
This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
The World News (WN) Network, has created this privacy statement in order to demonstrate our firm commitment to user privacy. The following discloses our information gathering and dissemination practices for wn.com, as well as e-mail newsletters.
We do not collect personally identifiable information about you, except when you provide it to us. For example, if you submit an inquiry to us or sign up for our newsletter, you may be asked to provide certain information such as your contact details (name, e-mail address, mailing address, etc.).
When you submit your personally identifiable information through wn.com, you are giving your consent to the collection, use and disclosure of your personal information as set forth in this Privacy Policy. If you would prefer that we not collect any personally identifiable information from you, please do not provide us with any such information. We will not sell or rent your personally identifiable information to third parties without your consent, except as otherwise disclosed in this Privacy Policy.
Except as otherwise disclosed in this Privacy Policy, we will use the information you provide us only for the purpose of responding to your inquiry or in connection with the service for which you provided such information. We may forward your contact information and inquiry to our affiliates and other divisions of our company that we feel can best address your inquiry or provide you with the requested service. We may also use the information you provide in aggregate form for internal business purposes, such as generating statistics and developing marketing plans. We may share or transfer such non-personally identifiable information with or to our affiliates, licensees, agents and partners.
We may retain other companies and individuals to perform functions on our behalf. Such third parties may be provided with access to personally identifiable information needed to perform their functions, but may not use such information for any other purpose.
In addition, we may disclose any information, including personally identifiable information, we deem necessary, in our sole discretion, to comply with any applicable law, regulation, legal proceeding or governmental request.
We do not want you to receive unwanted e-mail from us. We try to make it easy to opt-out of any service you have asked to receive. If you sign-up to our e-mail newsletters we do not sell, exchange or give your e-mail address to a third party.
E-mail addresses are collected via the wn.com web site. Users have to physically opt-in to receive the wn.com newsletter and a verification e-mail is sent. wn.com is clearly and conspicuously named at the point of
collection.If you no longer wish to receive our newsletter and promotional communications, you may opt-out of receiving them by following the instructions included in each newsletter or communication or by e-mailing us at michaelw(at)wn.com
The security of your personal information is important to us. We follow generally accepted industry standards to protect the personal information submitted to us, both during registration and once we receive it. No method of transmission over the Internet, or method of electronic storage, is 100 percent secure, however. Therefore, though we strive to use commercially acceptable means to protect your personal information, we cannot guarantee its absolute security.
If we decide to change our e-mail practices, we will post those changes to this privacy statement, the homepage, and other places we think appropriate so that you are aware of what information we collect, how we use it, and under what circumstances, if any, we disclose it.
If we make material changes to our e-mail practices, we will notify you here, by e-mail, and by means of a notice on our home page.
The advertising banners and other forms of advertising appearing on this Web site are sometimes delivered to you, on our behalf, by a third party. In the course of serving advertisements to this site, the third party may place or recognize a unique cookie on your browser. For more information on cookies, you can visit www.cookiecentral.com.
As we continue to develop our business, we might sell certain aspects of our entities or assets. In such transactions, user information, including personally identifiable information, generally is one of the transferred business assets, and by submitting your personal information on Wn.com you agree that your data may be transferred to such parties in these circumstances.