What other surfaces does water bead up on?

Answer 1

Surfaces on which water beads are called hydrophobic surfaces. That is, the water "fears" the surface. Water tends to bead up on these types of surfaces because it is more strongly attracted to itself (other water molecules) than the surface molecules.

Common hydrophobic surfaces include waxes, Teflon, and most plastics.

Answer 2

Water beads best on non-polar surfaces, such as waxy or oily surfaces. This is because the water molecules are not attracted to the non-polar surface, but they are attracted to each other. Therefore, the molecules will pull together into an efficient shape, with little contact with the surface and more contact with other water molecules. A sphere, or bead, is a shape that meets these qualifications. The attraction of water molecules by water molecules is known as cohesion.

Answer 3

Short answer:

Water beads form on a surface when the cohesion of the water molecules with each other is much greater than the adhesion of the water to the surface.

This phenomena, or the lack there of, is called wetting and has been studied for centuries. The cohesion of a liquid is directly related to the surface tension of a liquid. Water, which has a high surface tension, readily forms beads on materials which are hydrophobic, i.e. materials with a small adhesion to water. The waxed surface of a car has small adhesion and so water beads form regularly. The raw painted surface of the car would have more adhesion with water and so greater wettability. The opposite extreme, the tendency of a liquid to wet a surface due to strong adhesion, is critical to a situation such as lubrication where the liquid should coat the solid surface. It is the two properties combined, adhesion and cohesion, which determine wettabilty and beading.

Long Answer:

When one speaks of water beading on a surface, one means the formation of small droplets of water on a surface. This phenomena depends not only on the properties of water and the surface, but most importantly on the property of the interaction of the water with the surface. In science, this is the topic of "wetting" and one describes the tendency in terms of the "wettability" of a particular combination of liquid and surface. Beading is a manifestation of low wettability or little wetting.

A liquid droplet on a surface tends to form a more nearly spherical shape if the forces of attraction (or cohesion) between the liquid molecules is strong and the forces between the liquid and and the solid (adhesion) are weak. We associate strong cohesive forces of a liquid with a high surface tension and a high surface tension opposes wetting. Water is an example of a liquid with high surface tension.

The interaction of water with a surface like wax or plastic or Teflon is an example weak adhesion or weak forces between the liquid molecules and solid surface. Thus, wetting is highly unfavorable and formation of nearly spherical droplets is favored and we say water beads. Surfaces like metal or glass have somewhat stronger adhesive forces so wetting is greater and droplets are less spherical.

Contact Angle:

Wetting is not an on or off phenomena but varies in degree. The characteristic that provides a quantitative measure of wetting is called the contact angle. When a liquid like water is placed on a surface like teflon, the water forms a flattened droplet. The edge of the droplet makes an angle with the surface at the point of contact. We call that the contact angle, i.e. the angle between the solid surface and a tangent drawn to the surface of the droplet at the point of contact. This angle is measured on the side of the tangent that touches the water and so measures how much one would have to raise a horizontal line to match the liquid surface as one approaches the droplet from outside. This angle can be between zero and 180 degrees. If the droplet is very flat, the contact angle is small. If the droplet remained nearly spherical, then the contact angle would be zero near 180 degrees. It is important to note that this angle does not depend on the size of the droplet and even though gravity flattens a large droplet in the middle, when one approaches the edge, the contact angle is the same whether it is a small or large droplet.

When wetting is very poor, the contact angle large. This is the case for water droplets on wax, plastic, teflon and other surfaces with low wettability and hence a greater tendency toward beading. Water will wet glass more easily as well as a metal surface.

The contact angle for water on teflon is about 107 to 110 degrees but water on is only glass 53 degrees. This is different for metals too, where for instance, water on gold is 65 degrees and, depending on the plastic a value around plastic 62 degrees may be expected. Obviously all this depends on factors like temperature and surface roughness. These variables technologically important have been studied extensively and tens of thousands of examples are known.

Applications:

Obviously, one wants one's raincoat to bead water as well as the wax on one's car. But the opposite is true for a lubricant. One wants oil to adhere to a surface of a bearing and have a small contact angle, ideally a zero contact angle. Coatings are designed with wettabilty as a primary consideration. Cloth may be treated with material to prevent wetting, but that is also an example where the surface texture or roughness plays a critical role. Paint is an example of a coating that would be carefully evaluated for wettability depending on the application.

Much of Biology occurs at the interface of a watery compartment. Without the surface properties of water as they are, life would not exist.

Finally, without high surface tension and low adhesion, all those little bugs that walk on water would have no place to go.

Answer 4

Short answer:

Water beads form on a surface when the cohesion of the water molecules with each other is much greater than the adhesion of the water to the surface.

This phenomena, or the lack there of, is called wetting and has been studied for centuries. The cohesion of a liquid is directly related to the surface tension of a liquid. Water, which has a high surface tension, readily forms beads on materials which are hydrophobic, i.e. materials with a small adhesion to water. The waxed surface of a car has small adhesion and so water beads form regularly. The raw painted surface of the car would have more adhesion with water and so greater wettability. The opposite extreme, the tendency of a liquid to wet a surface due to strong adhesion, is critical to a situation such as lubrication where the liquid should coat the solid surface. It is the two properties combined, adhesion and cohesion, which determine wettabilty and beading.

Long Answer:

When one speaks of water beading on a surface, one means the formation of small droplets of water on a surface. This phenomena depends not only on the properties of water and the surface, but most importantly on the property of the interaction of the water with the surface. In science, this is the topic of "wetting" and one describes the tendency in terms of the "wettability" of a particular combination of liquid and surface. Beading is a manifestation of low wettability or little wetting.

A liquid droplet on a surface tends to form a more nearly spherical shape if the forces of attraction (or cohesion) between the liquid molecules is strong and the forces between the liquid and and the solid (adhesion) are weak. We associate strong cohesive forces of a liquid with a high surface tension and a high surface tension opposes wetting. Water is an example of a liquid with high surface tension.

The interaction of water with a surface like wax or plastic or Teflon is an example weak adhesion or weak forces between the liquid molecules and solid surface. Thus, wetting is highly unfavorable and formation of nearly spherical droplets is favored and we say water beads. Surfaces like metal or glass have somewhat stronger adhesive forces wetting is greater and droplets are less spherical.

Contact Angle:

Wetting is not an on or off phenomena but varies in degree. The characteristic that provides a quantitative measure of wetting is called the contact angle. When a liquid like water is placed on a surface like teflon, the water forms a flattened droplet. The edge of the droplet makes an angle with the surface at the point of contact. We call that the contact angle, i.e. the angle between the solid surface and a tangent drawn to the surface of the droplet at the point of contact. This angle is measured on the side of the tangent that touches the water and so measures how much one would have to raise a horizontal line to match the liquid surface as one approaches the droplet from outside. This angle can be between zero and 180 degrees. If the droplet is very flat, the contact angle is small. If the droplet remained nearly spherical, then the contact angle would be zero near 180 degrees. It is important to note that this angle does not depend on the size of the droplet and even though gravity flattens a large droplet in the middle, when one approaches the edge, the contact angle is the same whether it is a small or large droplet.

When wetting is very poor, the contact angle large. This is the case for water droplets on wax, plastic, Teflon and other surfaces with low wettability and hence a greater tendency toward beading. Water will wet glass wets more easily as well as a metal surface.

The contact angle for water on Teflon is about 107 to 110 degrees but water on is only glass 53 degrees. This is different for metals too, where for instance, water on gold is 65 degrees and, depending on the plastic a value around plastic 62 degrees may be expected. Obviously all this depends on factors like temperature and surface roughness. These variables technologically important have been studied extensively and tens of thousands of examples are known.

Applications:

Obviously, one wants one's raincoat to bead water as well as the wax on one's car. But the opposite is true for a lubricant. One wants oil to adhere to a surface of a bearing and have a small contact angle, ideally a zero contact angle. Coatings are designed with wettabilty as a primary consideration. Cloth may be treated with material to prevent wetting, but that is also an example where the surface texture or roughness plays a critical role. Paint is an example of a coating that would be carefully evaluated for wettability depending on the application.

Much of biology occurs at the interface of a watery compartment. Without the surface properties of water as they are, life would not exist.

Finally, without high surface tension and low adhesion, all those little bugs that walk on water would have no place to go.

Answer 5

H2O is a bonded compound, and is held together by the bonds, that want more water to bond to and causes water to pull together in a "beaded" form.