165 degree angle of contact with water on the surface modified using plasma technology Surface chemistry system. The contact angle is red angle plus 90 degrees.
Water drops on the hydrophobic surface of grass
Term hydrophobic comes from the Ancient Greek ὑδρόφοβος, "having the terror of water", constructed from ὕδωρ, "water", and φόβος, "fear".
Chemical background
Hydrophobic interaction is primarily an entropic effect resulting from the breaking of highly dynamic hydrogen bonds between water molecules by a liquid nonpolar solute forming a clathrate-like structure around the nonpolar molecules. This structure forms more highly ordered than free water molecules due to the water molecule positioning itself to interact as much as possible with itself, and thus results in a higher entropy state, which causes non-polar molecules to cluster together to reduce surface area , exposed to water and reducing the entropy of the system. Thus, the 2 immiscible phases (hydrophilic versus hydrophobic) will change in such a way that their respective interfacial area will be minimal. This effect can be visualized in a phenomenon called phase separation.
Superhydrophobicity
Drop of water on a lotus leaf plant.
Superhydrophobic surfaces, such as the leaves of the lotus plant, are those that are extremely difficult to wet. The contact angles of water drops exceed 150°. This is referred to as the lotus effect, and is primarily a physical property related to interfacial tension rather than a chemical property.
theory
In 1805, Thomas Young determined the contact angle & thetas by analyzing the forces acting on the fluid at rest of a drop on a solid surface surrounded by gas.
WENZEL established that when the liquid is in direct contact with the microstructural surface, θ will change to θ W*
cos θ W * = r cos θ (\displaystyle \cos (\theta)_(W)*=r\cos (\theta)\,)Where R represents the ratio of the actual area to the projected area. The Wenzel equation shows that microstructuring a surface enhances the natural tendency of the surface. A hydrophobic surface (one that has an original contact angle greater than 90°) becomes more hydrophobic when microstructured - its new contact angle becomes greater than the original. However, a hydrophilic surface (one that has an original contact angle of less than 90°) becomes more hydrophilic when microstructured - its new contact angle will become smaller than the original. Cassie and Baxter discovered that if liquid is suspended on the tops of microstructures, θ will change to & thetas CB*:
cos θ CB * = φ (cos θ + 1) - 1 (\displaystyle \cos (\theta)_(\text (CB))*=\varphi (\cos \theta +1)-1\, )where φ is the fraction of the area of the solid that is in contact with the liquid. Liquid in the Cassie-Baxter state is more mobile than in the Wenzel state.
We can predict whether a Wenzel or Cassie-Baxter state should exist by calculating the new contact angle from both equations. When minimizing the free energy argument, the ratio predicted by the smaller new contact angle is the state most likely to exist. Stated in mathematical terms, for a Cassie-Baxter state to exist, the inequality holds must be true.
cos θ > φ - 1 r - φ (\displaystyle \\cos theta>(\frac (\varphi -1)(r-\varphi)))A recent alternative criterion for the Cassie-Baxter state states that the Cassie-Baxter state exists if the following 2 conditions are met: 1) the lines of contact of the forces overcome the body forces of the unsupported weight of the drop and 2) the microstructure is high enough to prevent the liquid that bridges the microstructures from touching microstructure base.
A new criterion for switching between Wenzel and Cassie-Baxter states was developed recently based on surface roughness and surface energy. The criterion focuses on the ability of air to trap liquid droplets on uneven surfaces, which could tell whether the Wenzel model or the Cassie-Baxter model should be used for a particular combination of surface roughness and energy.
Contact angle is a measure of static hydrophobicity, and contact angle hysteresis and sliding angle are dynamic measures. Contact angle hysteresis is a phenomenon that characterizes surface heterogeneity. When a pipette injects liquid onto a solid, the liquid will form some contact angle. As the pipette injects more liquid, the droplet will increase in volume, the contact angle will increase, but its three-phase boundary will remain stationary until it suddenly moves outward. The contact angle of the droplet was just before advancing outward is called the advancing contact angle. The retreating contact angle is now measured by pumping liquid back out of the droplet. The droplet will decrease in volume, the contact angle will decrease, but its three-phase boundary will remain motionless until it suddenly retreats inward. The contact angle of the droplet was just before retreating inward is called the receding contact angle. The difference between advancing and retreating contact angles is called contact angle hysteresis and can be used to characterize surface heterogeneity, roughness, and mobility. Surfaces that are not homogeneous will have domains that impede the movement of the contact line. The sliding angle is another measure of dynamic hydrophobicity and is measured by depositing a drop on a surface and tilting the surface until the drop begins to slide. In general, fluids in the Cassie-Baxter state exhibit lower sliding angles and contact angle hysteresis than those in the Wenzel state.
Research and Development
Dettre and Johnson discovered in 1964 that the superhydrophobic lotus effect phenomenon was associated with rough hydrophobic surfaces, and they developed a theoretical model based on experiments with glass beads coated with paraffin or TFE telomer. The self-cleaning properties of superhydrophobic micro-nanostructured surfaces were reported in 1977. Perfluoroalkyl, perfluoropolyether, and RF plasma-formed superhydrophobic materials were developed, used for electrowetting, and commercialized for biomedical applications between 1986 and 1995. Other technologies and applications have emerged since the mid-1990s . A durable superhydrophobic hierarchical composition, applied in one or two steps, was disclosed in 2002, containing nano-sized particles ≤ 100 nm, applied to a surface having micron-sized features or particles ≤ 100 µm. Larger particles were observed to protect small particles from mechanical wear.
In a recent study, superhydrophobicity was reported, allowing alkyl ketene dimer (AKD) to solidify into nanostructured fractal surfaces. Many papers present fabrication methods for making superhydrophobic surfaces, including particle deposition, sol-gel methods, plasma processing, vapor deposition, and casting technologies. Current opportunities for impact research lie primarily in basic research and practical production. Debate has recently emerged regarding the applicability of the Wenzel and Cassie-Baxter models. In an experiment designed to challenge the surface energy perspective of the Wenzel and Cassie-Baxter model and promote the contact line perspective, water droplets were placed on a smooth hydrophobic site in a rough hydrophobic region, a rough hydrophobic site in a smooth hydrophobic region, and a hydrophilic site in a hydrophobic region. Experiments showed that the surface chemistry and geometry at the contact line were affected by the contact angle and contact angle hysteresis, but the surface area inside the contact line had no effect. The argument that increasing jaggedness in the contact line increases droplet mobility has also been proposed.
Hydrophilic and hydrophobic substances... and got the best answer
Answer from Mikhail[guru]
In relation to water, practically all substances can be divided into two groups:
1. Hydrophilic (from the Greek “phileo” - to love, having a positive affinity for water). These substances have a polar molecule, including electronegative atoms (oxygen, nitrogen, phosphorus, etc.). As a result, individual atoms of such molecules also acquire partial charges and form hydrogen bonds with water molecules. Examples: sugars, amino acids, organic acids.
2. Hydrophobic (from the Greek “phobos” - fear, having a negative affinity for water). The molecules of such substances are non-polar and do not mix with a polar solvent, such as water, but are highly soluble in organic solvents, for example, ether, and in fats. An example is linear and cyclic hydrocarbons. including benzene as well as oxides, hydroxides, silicates, sulfates, phosphates, clays, etc., substances with polar groups -OH, -COOH, -NO2, etc.
Organic hydrophilic substances:
Ethyl mercuric phosphate (C2H5Hg)3P04 - white crystalline substance, mp. 178 °C. It dissolves well in water and hydrophilic organic solvents, less so in hydrocarbons and other hydrophobic solvents. With water it produces crystalline hydrates, which easily lose water when heated. An anhydrous drug, when stored in a humid atmosphere, forms a crystalline hydrate with one molecule of water (mp 110 °C).
Feyylmercurtriethanol ammonium lactate (8) - white crystalline substance, mp. 126 °C. Highly soluble in water and hydrophilic organic solvents. LD50 30 mg/kg.
Most organic substances with hydrocarbon radicals, metals, semiconductors, etc. have hydrophobicity (poor wettability). Hydrophobic substances serve to protect products from the destructive effects of water.
Answer from 2 answers[guru]
Hello! Here is a selection of topics with answers to your question: Hydrophilic and hydrophobic substances...
Help with biology! What substances are called hydrophilic, hydrophobic? Give examples. (3-4 sentences.)
Water is an excellent solvent for polar substances such as salts, sugars, alcohols,
The term hydrophilicity (derived from the ancient Greek words “water” and “love”) is a characteristic of the intensity of interaction of a substance with water at the molecular level, that is, the ability of a material to intensively absorb moisture, as well as the high wettability of water by the surface of the substance. This concept can be applied to solids, as a property of the surface, and to individual ions, atoms, molecules and their groups.
Hydrophilicity is characterized by the magnitude of the bond between adsorption water molecules and the molecules of a substance; in this case, compounds are formed in which the amount of water is distributed according to the bond energy values.
Hydrophilicity is inherent in substances that have ionic crystal lattices (hydroxides, oxides, sulfates, silicates, clays, phosphates, glasses, etc.) that have polar groups -OH, -NO 2, -COOH, etc. Hydrophilicity and hydrophobicity- special cases of interaction of substances with solvents (lyophilicity, lyophobicity).
Hydrophobicity can be considered as a small degree of hydrophilicity, because the action of intermolecular forces of attraction will always be more or less present between the molecules of any body and water. Hydrophilicity and hydrophobicity can be distinguished by the way a drop of water spreads on a body with a smooth surface. The drop will spread completely on the hydrophilic surface, and partially on the hydrophobic one, while the value of the angle formed between the surface of the wetted material and the drop is influenced by the degree of hydrophobicity of the given body. Hydrophilic substances are substances in which the strength of molecular (ionic, atomic) interactions is quite strong. Hydrophobic are metals that are devoid of oxide films, organic compounds that have hydrocarbon groups in the molecule (waxes, fats, paraffins, some plastics), graphite, sulfur and other substances that have weak interactions at the intermolecular level.
The concepts of hydrophilicity and hydrophobicity are applied both in relation to bodies and their surfaces, and in relation to individual molecules or individual parts of molecules. For example, the molecules of surface active substances contain polar (hydrophilic) and hydrocarbon (hydrophobic) compounds. The hydrophilicity of the surface part of the body can change dramatically due to the adsorption of such substances.
Hydrophilization is the process of increasing hydrophilicity, and hydrophobization is the process of decreasing it. These phenomena are of great importance in the cosmetics industry, in textile technology for hydrophilization of fabrics (fibers) to improve the quality of washing, bleaching, dyeing, etc.
Hydrophilicity in cosmetics
The perfumery and cosmetics industry produces hydrophilic creams and gels that protect the skin from impurities that are not soluble in water. Such products contain hydrophilic components that form a film that prevents the penetration of water-insoluble pollutants into the surface layer of the skin.
Hydrophilic creams are made from an emulsion that is stabilized with suitable emulsifiers or with a water-oil-water or oil-water base. In addition, these include dispersed colloidal systems in which hydrophilic surfactant components are stabilized and consisting of water-dispersed or water-glycol mixed solvents of higher fatty acids or alcohols.
Hydrogels (hydrophilic gels) are prepared from bases consisting of water, a mixed non-aqueous or hydrophilic solvent (ethyl alcohol, propylene glycol, glycerin) and a hydrophilic gelling agent (cellulose derivatives, carbomers).
Hydrophilic properties of creams and gels:
· quickly and well absorbed;
· nourish the skin;
· after their use there is no feeling of greasyness;
· cleanse the skin;
· have a strengthening effect on the skin;
· reduce the effect of negative environmental factors;
Help the skin maintain its natural ability to regenerate.
Hydrophilic creams and gels are designed to protect the skin when working with water-immiscible oils, fuel oil, petroleum, paints, resins, graphite, soot, organic solvents, cooling and lubricating solutions, construction foam and numerous other mildly aggressive substances. They are also indispensable when repairing a car, renovating an apartment, during construction, in the country when working with fertilizers and soil.
The KorolevPharm company produces various types of perfumery and cosmetic products, including hydrophilic and hydrophobic creams. The company is a contract manufacturer and carries out all stages of production: development of recipes, certification, launching production, serial production of products. The production site is equipped with modern equipment.
The enterprise is certified for compliance with the requirements
HYDROPHILICITY AND HYDROPHOBICITY (from the Greek hydor - water and philia - love or phobos - fear, fear * a. wetting ability hydrophoby; n. Hydrophilie und Hydrophobie; f. hydrophilite et hydrophobie; i. hidrofilia e hidrofobia) - concepts characterizing affinity substances or bodies formed by them; this affinity is due to the forces of intermolecular interaction. The concepts of hydrophilicity and hydrophobicity can apply equally to a substance, to the surface of a body, and to a thin layer (in the limit, one molecule thick) at the interface between phases (bodies). Hydrophilicity and hydrophobicity are a special case of lyophilicity and lyophobicity - characteristics of the molecular interaction of substances with various liquids.
A general measure of hydrophilicity is the binding energy of water molecules to the surface of the body; it can be determined by the heat of wetting if the substance of a given body is insoluble. Hydrophobicity is considered as a low degree of hydrophilicity, because Between the molecules of water and any body, intermolecular forces of attraction always act to a greater or lesser extent. Hydrophilicity and hydrophobicity can be assessed by the spreading of a drop of water on a smooth body surface (Fig.); characterized by the contact angle; on a hydrophilic surface the drop spreads completely, on a hydrophobic surface it spreads partially, and the angle between the surfaces of the drop and the wetted body depends on how hydrophobic the body is.
All bodies in which the intensity of molecular (atomic, ionic) interactions is sufficiently high are hydrophilic. Hydrophilicity is especially pronounced with ionic crystal lattices (for example, etc.), as well as silicate glasses. Metals that lack oxide films, organic compounds with a predominance of hydrocarbon groups in the molecule (for example, paraffins, fats, waxes, some plastics), and other substances with weak intermolecular interactions are hydrophobic.
The concepts of hydrophilicity and hydrophobicity apply not only to bodies or their surfaces, but also to single molecules or individual parts of molecules. Thus, in the molecules of surfactants, hydrophilic (polar) and hydrophobic (hydrocarbon) groups are distinguished. The hydrophilicity of the body surface can change dramatically as a result of the adsorption of such substances. An increase in hydrophilicity is called hydrophilization, and a decrease is called hydrophobization. Both phenomena play an important role in the method. Hydrophilization results in selective gangue minerals. For these purposes, organic (starch, dextrin, etc.) and inorganic (liquid glass, sodium cyanide, etc.) reagents are used. Hydrophobization is caused by the addition of special collecting reagents. See also .
Some people at school were lucky in chemistry lessons not only to write boring tests and calculate molar mass or indicate valency, but also to watch how the teacher conducts experiments. Invariably, as part of the experiment, as if by magic, the liquids in the test tubes changed color unpredictably, and something else could explode or burn beautifully. Perhaps not as impressive, but still interesting are experiments in which hydrophilic and hydrophobic substances are used. By the way, what is this and why are they curious?
Physical properties
In chemistry lessons, when going through another element from the periodic table, as well as all the basic substances, we always talked about their various characteristics. Their physical properties were also touched upon: density under normal conditions, melting and boiling points, hardness, color, electrical conductivity, thermal conductivity and many others. Sometimes there was talk about such characteristics as hydrophobicity or hydrophilicity, but, as a rule, they do not talk about this separately. Meanwhile, this is a rather interesting group of substances that can easily be encountered in everyday life. So it would be useful to learn more about them.
Hydrophobic substances
Examples can easily be taken from life. So, you cannot mix water with oil - everyone knows this. It simply does not dissolve, but remains floating in bubbles or a film on the surface, since its density is lower. But why is this and what other hydrophobic substances exist?
This group usually includes fats, some proteins, and silicones. The name of the substances comes from the Greek words hydor - water and phobos - fear, but this does not mean that the molecules are afraid. They are simply slightly or completely insoluble; they are also called non-polar. Absolute hydrophobicity does not exist; even those substances that, it would seem, do not interact with water at all, still adsorb it, albeit in negligible quantities. In practice, the contact of such a material with H 2 O appears in the form of a film or droplets, or the liquid remains on the surface and takes the shape of a ball, since it has the smallest surface area and provides minimal contact.
Hydrophobic properties are explained by certain substances. This is due to the low rate of attraction to, as it happens, for example, with hydrocarbons.
Hydrophilic substances
The name of this group, as you might guess, also comes from Greek words. But in this case, the second part of philia is love, and this perfectly characterizes the relationship of such substances with water - complete “mutual understanding” and excellent solubility. This group, sometimes called "polar", includes simple alcohols, sugars, amino acids, etc. Accordingly, they have these characteristics because they have a high energy of attraction to the water molecule. Strictly speaking, in general, all substances are hydrophilic to a greater or lesser extent.
Amphiphilicity
Does it happen that hydrophobic substances can simultaneously have hydrophilic properties? It turns out yes! This group of substances is called amphiphilic or amphiphilic. It turns out that the same molecule can have in its structure both soluble - polar and water-repellent - non-polar elements. For example, some proteins, lipids, surfactants, polymers and peptides have such properties. When interacting with water, they form various supramolecular structures: monolayers, liposomes, micelles, bilayer membranes, vesicles, etc. Polar groups are oriented towards the liquid.
Meaning and application in life
In addition to the interaction of water and oil, one can find a lot of evidence that hydrophobic substances are found almost everywhere. Thus, clean surfaces of metals, semiconductors, as well as animal skin, plant leaves, and the chitinous cover of insects have similar properties.
In nature, both types of substances are important. Thus, hydrophiles are used in transport in the organisms of animals and plants; the end products of metabolism are also excreted using solutions of biological fluids. Nonpolar substances are of great importance in the formation of cell membranes, which have That is why such properties play an important role in the course of biological processes.
In recent years, scientists have been developing new hydrophobic substances that can be used to protect various materials from wetting and contamination, thus creating even self-cleaning surfaces. Clothing, metal products, building materials, car glass - there are many areas of application. Further study of this topic will lead to the development of multiphobic substances that will become the basis for stain-resistant surfaces. By creating such materials, people will be able to save time, money and resources, and it will also be possible to reduce the degree of cleaning products. So further developments will benefit everyone.
