Surface properties change with the chemical composition. Due to the presence of specific moieties or the general chemical nature, the substrate may exhibit hydrophobic, hydrophilic or amphiphilic properties. But what are they and how do they affect our lives?
Hydrophilic properties (which means “water-loving” from Greek) is the ability to attract substances of a polar nature. Polar molecules have in their structure places that accumulate negative and positive charges, and are kind of microscopic magnets, which strongly attract (on the principle of different poles: “+”attracts “-“). An example of a polar substance is water. It is polarity that provides water with unprecedented properties that it would not have had if it were not for them. Water molecules, which are small magnets, attract each other, making them clump together so that under normal conditions water is a liquid. During evaporation, we must provide a large amount of energy because during that process is necessary breaking hundreds of billions of small electromagnetic interactions. All substances with this type of character will be “compatible” with water (i.e. hydrophilic) and will be wetted or dissolved. What is a hydrophilic substance? Sugar, ethanol, salt, vinegar or glycerin because they dissolve in water, cotton, glass and wood because they are moistened by water. This is related to the chemical structure of these substances – sugar, ethanol, vinegar and glycerine have polar moieties (-OH or -COOH) and a small hydrocarbon backbone (which is non-polar), the salt is ionic (and the ions have charges “+” or “-” so they are electromagnetically active), while cotton or wood contain hydrophilic components that are organic polymers (cellulose, hemicellulose and others) having numerous hydrophilic moieties (-OH). The glass is made of silicon oxide which has hydrophilic oxygen groups.
However, it is different with hydrophobic substances. They do not have polar groups and do not have charges “+” and “-” on the surface, so they are not electromagnetically active. Among similar substances, they exhibit hydrophobic interactions and definitely prefer similar substances. These include: hydrocarbons, e.g. petrol or paraffin, fats or waxes. It is impossible to dissolve them in water, but they willingly join together. Water flows freely over them because they are hydrophobic (from Greek “they are afraid of water”).
There is also a third group of compounds – amphiphilic substances. They dissolve in both polar and non-polar substances because they have two regions in the molecule – hydrophobic and hydrophilic (the so-called head and tail). These types of substances are soaps and detergents. Thanks to them, the dishwashing liquid dissolve fat on the dishes and then stick to the water to form micelles.
Surfaces with a hydrophilic character are easy to wet and water dissolves after them. The hydrophobic surfaces repels water which drops in the drops (to limit the surface contact with the substrate) and flows down easily on it. The hydrophobic surfaces gain the so-called self-cleaning properties – after wetting dirt dissolves in water and leaves the surface with it. This is a very desirable feature on surfaces that frequently come into contact with water, such as car paint, glass or building facades.
The hydrophilicity of the surface is determined by a simple rule – if the contact angle of water drop is less than 90 degrees, the surface is hydrophilic. When it exceeds 90 degrees, the surface becomes hydrophobic. When the contact angle far exceeds 90 degrees it acquires superhydrophobic properties. These dependences are illustrated in the figure below.
The coatings produced by ITP-System allow for permanent hydrophobic properties for any surface. We have developed technologies that allow for permanent hydrophobic functionalization without losing the ability of “breathing” the substrate (our coatings do not fill the micropores of the substrate only change their surface at the nano scale). This prevents the substrate from retaining water (which can, for example, be absorbed from another source, e.g. the wall may get wet from a leaky pipe installed in it!).
Hydrophobic coatings are the perfect effect, self-cleaning properties, labor and energy savings!