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Hydrophobic refers to a fear of mixing or interacting with water under a certain set of reaction conditions. Hydrophobicity is a term used in general science to describe a substance’s capacity to resist water.
The name “hydrophobicity” comes from two Greek words: “hydro,” which means “water,” and “phobos,” which means “fear.” As a result, hydrophobic substances are those that commonly display the feature of hydrophobicity.
What is Hydrophobic?
Materials with a special affinity for water – those it spreads across, maximizing contact – are known as hydrophilic. Those that naturally repel water, causing droplets to form, are known as hydrophobic. Nonpolar molecules are those that aren’t polar. Non-polar molecules, in particular, do not seem to have distinct charges, therefore no positive and negative poles are generated. Furthermore, it may be deduced that the electrical charges in non-polar molecules are spread evenly throughout the whole molecule.
Scientists have clearly proven that “like dissolves like.” As a result, hydrophobic compounds are miscible with non-polar liquids, the majority of which are organic solvents. It’s worth noting that, because water is polar, the bond between water and hydrophobic molecules is relatively weak. Aside from hydrophobic materials, the literature mentions a number of superhydrophobic materials.
Super-hydrophobic materials resist wetting because their contact angle with water is more than 150 degrees (the ability of a liquid to maintain contact with a solid surface). The super hydrophobicity of molecules, on the other hand, is a consequence of interfacial tension rather than a chemical characteristic of matter. The Lotus effect refers to the shape created by water droplets on hydrophobic surfaces.
The emergence of water droplets on the surface of lotus leaves is one of the most common examples of the lotus effect, which is also employed in textile manufacturing for self-cleaning purposes. Lacking an affinity for water; insoluble in water; resisting water (biology term). Alkanes, oils, fats, and greasy compounds in general are examples of hydrophobic molecules.
Example of Hydrophobic Substances
Both the household and industrial sectors include a variety of hydrophobic chemicals. Hydrophobic substances include alkanes, oils, fats, greasy chemicals, and the vast majority of organic molecules. The removal of oil from aqueous solutions, the management of oil spills, and the chemical separation process to separate non-polar components from polar elements are all uses of hydrophobic substances. Because water is polar and fats and oils are non-polar and highly hydrophobic, it is a frequent observation that when oil or fats are combined with water, two separate layers emerge that are immiscible with each other.
Animals and plants both exhibit hydrophobicity in different ways. Many plants are hydrophobic by nature, indicating that the leaves have hydrophobic coats on their surfaces. The coating’s primary function is to prevent water and rain from adsorbing into the leaves, which obstructs the passage of nutrients. The movement of nitrites in plants is determined by the flow of water from roots to leaves. As a result, if the leaf surfaces are not hydrophobic, the osmosis process and therefore osmotic pressure will be disrupted, which will have a significant impact on plant nutrition.
The process of hydrophobicity is similarly important in birds. Birds’ hydrophobic bodies and feathers prevent water from penetrating their bodies, preventing excessive weight gain and aiding them in smooth flight.
Hydrophobic and Hydrophilic Substances
Water-loving polar molecules are known as hydrophilic compounds. Sugar, salt, starch, and cellulose are examples of compounds that are easily soluble in water. Hydrophilicity is the degree to which the surface of hydrophilic molecules attracts water molecules. Hydrophobic, on the other hand, is water repellent and, as a result of its non-polar nature, is not miscible in water. Some of the most frequent chemical groups discovered in hydrophobic compounds are-CH3,-CH2-CH3,-R-C6H5 and C2H2, whereas hydrophilic substances include-OH,-COOO-, and-NH-.
Hydrophobic and Lipophilic
The phrases hydrophobic and lipophilic are sometimes used interchangeably, yet the two words refer to completely distinct phenomena. Water repelling compounds are hydrophobic, whereas fat-loving ones are lipophilic. Except for silicones and fluorocarbons, most hydrophobic compounds are lipophilic in nature, according to diverse publications.
Under the umbrella of hydrophobic interactions, the interactions between water and hydrophobes are extensively characterised. A good example of such interactions is the relative mixing of water and fat. The hydrogen bonds in the water molecule break when a hydrophobe is placed in an aqueous solution, however this does not ensure that the water molecule will interact with the hydrophobic materials. Furthermore, heat must be applied to the system in order to break the strong hydrogen bond, making the process endothermic.
Around the surface of the hydrophobe, new hydrogen bonds create an ice-like cage structure known as a clathrate cage. The system becomes more organised when the clathrate cage is oriented in this way, and the total entropy (a measure of disorderliness) of the system decreases. The intensity of hydrophobic interactions is also affected by temperature, the amount of carbon atoms in the hydrophobe, as well as the shape and size of the hydrophobic molecule.
Biological Importance of Hydrophobic Interactions
Protein folding relies heavily on hydrophobic interactions to keep it stable and physiologically active. Proteins will be able to decrease their surface area and avoid unwanted interactions with water molecules as a result of these interactions. Similarly, hydrophobic interactions are essential for the survival and optimal functioning of the phospholipid bilayer membranes found in every cell in the human body.
Advantages of Hydrophobes
Hydrophobic compounds provide several advantages in both home and industrial uses. Hydrophobes are low-energy surface materials that are resistant to wetting and have better corrosion resistance. These chemicals are utilised in moisture detection instruments as well as heat trace tubing and analytical sample transfer systems to prevent moisture contamination. In addition, hydrophobes are used in HPLC medical diagnostics to enhance separation and corrosion resistance. Similarly, anti-biofouling coatings for boots, metal refining, stain-resistant fabrics, oil and water separation in the textile sector, and the manufacturing of fire retardant and waterproof clothing all employ hydrophobic surfaces.
Measurement of Hydrophobicity
Various analytical methods, such as hydrophobic interaction chromatography, contact angle measurement, and rose bengal measurement, can be used to determine hydrophobicity. It’s worth noting that while evaluating hydrophobicity, the identification of groups present in the particle is critical. The most common approach to calculating the hydrophobicity of a surface is to determine the contact angle between the droplets of water and the surface itself. The water droplet running over a hydrophobic surface generally maintains a contact angle of greater than 90 degrees and preserves its spherical form. Furthermore, superhydrophobic materials have a contact angle of greater than 150 degrees.
Water droplets spread out far when they come into contact with hydrophilic surfaces, and the contact angle is usually less than 90 degrees. The angle is less than 5 degrees for super hydrophilic, less than 90 degrees for hydrophilic, and 90-150 degrees and 150-180 degrees for hydrophobic and superhydrophobic, respectively. The higher the contact angle between the water droplet and the hydrophobes, the stronger the liquid-liquid interaction rather than the liquid surface interaction, making the surface hydrophobic.
Hydrophobic substances, in conclusion, are those that are not miscible in water. Non-polar liquids, mostly organic solvents, are miscible with hydrophobes. Because water is a polar molecule, the bond between it and hydrophobic substances is very weak, and when they come into contact, they create two separate and distinct layers. Hydrophobic substances include alkanes, oils, fats, and greasy chemicals. Plants and birds both go through the hydrophobicity process. The hydrophobic coating found on the surface of the leaves, which prevents water from entering through them, prevents the interruption of the flow of nutrients in plants. As a result, water continues to flow from the base to the top of the plant, transporting essential nutrients from the soil to their destination.
Similarly, hydrophobicity prevents water from entering the bodies of birds via feathers, skin, and aquatic creatures, preventing them from becoming overweight and facilitating smooth flight. Furthermore, the contact angle between the water droplet and the hydrophobe’s surface may be calculated to determine hydrophobicity. The water droplet running over a hydrophobic surface generally maintains a contact angle of greater than 90 degrees and preserves its spherical form.
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