Hydrophobic interactions describe the relations between water and hydrophobes low water-soluble molecules. Hydrophobes are nonpolar molecules and usually have a long chain of carbons that do not interact with water molecules.
The mixing of fat and water is a good example of this particular interaction. However, this is not the case. The behavior of a fat droplet in water has more to do with the enthalpy and entropy of the reaction than its intermolecular forces.
American chemist Walter Kauzmann discovered that nonpolar substances like fat molecules tend to clump up together rather than distributing itself in a water medium, because this allow the fat molecules to have minimal contact with water.
The image above indicates that when the hydrophobes come together, they will have less contact with water. They interact with a total of 16 water molecules before they come together and only 10 atoms after they interact. How various coatings can be used to achieve the desired water repelling property.
Learn about oil repelling surfaces oleophobic Learn about superhydrophobic coatings. Learn about hydrophilic coatings. Have a Question? Contact Our Technical Service Team.
Recommended Reading. Leave A Comment. Download E-Book. Recent Posts. Subscribe To Email Updates. Ready To Talk? Contact Us Email Us. Call Us Email Us. Our Blog. Subscribe to Email Updates. Level Elementary. Middle School. High School. Full-Size Photo:. Files: Files:. Teacher Preparation Guide. New hydrogen bonds form that shape into an ice-like cage structure known as a clathrate cage around the surface of the hydrophobe.
This orientation of the clathrate cage makes the system more structured and the total entropy a measure of disorderliness of the system is decreased. Furthermore, the strength of the hydrophobic interactions depends on the temperature, the number of carbon atoms present in the hydrophobe, and the shape and dimensions of the hydrophobic molecule [3].
The hydrophobic interactions are very important in protein folding making it stable and biologically active. The interactions will give a chance to protein to reduce its surface and to avoid the undesired interactions with the water molecule. Similarly, the phospholipid bilayer membranes present in every cell in the human body also depend on the hydrophobic interactions for their survival and optimum functioning. There are many advantages to employing hydrophobic substances for domestic and industrial applications.
Hydrophobes are usually low-energy surface materials that resist wetting and have improved corrosion resistance. Such substances are used for improved moisture detection instrumentations and to prevent moisture contamination in heat trace tubing and analytical sample transfer systems. Moreover, hydrophobes are also employed in HPLC medical diagnostics improved separation and corrosion resistance systems. Similarly, the hydrophobic surfaces are used in anti-biofouling paints for boots, refining of metals, stain-resistant textiles, the separation of oil and water, in the textile industry, and the manufacture of fire retardant and waterproof clothes [4].
The hydrophobicity can be measured by various analytical techniques such as hydrophobic interaction chromatography , contact angle measurement , and rose bengal measurement. It is worth mentioning here that the identification of groups present in the particle is very important while measuring hydrophobicity.
The most frequent method that has been used to calculate the hydrophobicity of the surface is via the calculation of contact angle in between the droplets of water and the surface itself. A contact angle of more than 90 degrees is usually maintained by the water droplet flowing over a hydrophobic surface and retains a spherical shape.
Moreover, the superhydrophobic materials possess a relatively larger contact angle of above degrees. Upon contact with the hydrophilic surfaces, the droplets of water spread out far and the contact angle is generally small and is less than 90 degrees. The water contact angle between the water droplet and the various surfaces has been given in Fig 2.
For super hydrophilic, the angle is less than 5 degrees, for hydrophilic the angle is less than 90 degrees and for hydrophobic and superhydrophobic the angles are degrees and degrees respectively.
It can be concluded that the larger the contact angle in between the water droplet and hydrophobes, the stronger is the liquid-liquid interaction rather than liquid surface interaction thus making the surface hydrophobic [5]. It can be concluded that hydrophobic substances are those that are not miscible in water.
Hydrophobes are miscible in non-polar liquids that are mainly organic solvents. Water is a polar molecule, hence the affiliation between water and hydrophobic substances is very minute and thus they form two separate and distinct layers with each other when brought in contact. Alkanes, oils, fats, and greasy compounds are hydrophobic in nature. The process of hydrophobicity can be found in both plants and birds. In plants, the interruption of the flow of nutrients is avoided by the hydrophobic layer present on the surface of the leaves that avoid the entrance of water through them.
Hence, the flow of water remains from the root to the top of the plant carrying necessary nutrients from the soil to the destination.
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