Adhesion is the attraction between two dissimilar phases. The first thing that comes to mind when talking about adhesion is naturally gluing. However, adhesion plays an important role in many other daily and industrial processes. Adhesion can also be either wanted or unwanted.
Adhesion of coating on the surface
Probably one of the most obvious examples of adhesion is the adhesion of different types of coatings. Whether you are painting the wall or adding a polymer layer on a package, adhesion is of utmost importance for the outcome of the process.
There are several approaches to how adhesion can be improved in coating processes. In practice, they can be divided into two; modification of coating formulation or the substrate where the coating is applied. As adhesion is dependent on the wettability, the wetting agent is often added to coating formulation to reduce the surface tension and improve the spreading of the coating. This is done for example in paints. In addition, the paint manufacturer might recommend cleaning or another type of priming of the surface before painting.
In industrial processes such as lamination and printing, the modification of the substrate is a common approach. The surface is plasma treated to increase its surface energy which improves the spreading of the coating material on it.
Adhesion of proteins on biomaterials
In biomedical applications, the adhesion of proteins is typically unwanted. In blood-contacting medical devices, the adsorption of proteins occurs immediately and initiate a thrombosis cascade and bacterial infection. This will ultimately lead to decreased device safety. In diagnostic and biosensor applications, the protein adsorption leads to biofouling and limits the sensitivity and lifetime of these devices.
Poor resistance to protein adsorption and adhesion is associated with the hydrophobic surface. Polymeric biomaterials are often used based on their bulk mechanical properties. The downside of the polymers is their inherently hydrophobic surface. Several approached to render the polymeric materials hydrophilic have been studied to make the materials protein resistant.
Adhesion of oil on the rock
In enhanced oil recovery, the adhesion of oil on the rock is one of the most important aspects to consider. The oil reservoirs can be classified as oil-wet, intermediate-wet, or water-wet depending on the wetting characteristics of the reservoir rock. In principle, the oil yield is higher in the water-wet reservoirs whereas, in the oil-wet reservoirs additional, enhanced oil recovery methods are required to release the oil. One of the main mechanisms of the enhanced oil recovery is to alter the wettability of the reservoir to be more water-wet. This can be achieved with several different methods, such as flooding of surfactants or other chemicals into the reservoir, or with thermal methods.
To hear more about adhesion, please listen the pod episode through the link below.
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