”English definition of "hydrophilicity": hydrophilic property; hydrophility, which meansPolar groupMolecules ofwaterIt has greater affinity, can attract water molecules, or is easily dissolved in water.
havePolar groupMolecules ofwaterIt has great affinity and can attract or dissolve water molecules.Formed by such moleculesSolid materialsThe surface ofwetting。With this characteristic, they are all materialHydrophilicity。
Hydrophilicity refers to the ability of molecules to penetratehydrogen bondTemporarily bonded with waterphysical property。Because it is thermodynamically appropriate, this molecule can be dissolved not only in water, but also in otherPolar solutionInside.OneHydrophilic molecule, or the hydrophilic part of the molecule, refers to its ability topolarizationTo the position where hydrogen bond can be formedHydrophobic solutionIt is easier to dissolve in water.Hydrophilicity andHydrophobicityMolecules can also be calledPolar moleculeandNonpolar molecule。
Soap has both hydrophilic and hydrophobic ends, so that it can be dissolved in water or oil.Therefore, soap can remove the interface between water and oil.
The material hasAffinityPerformance.Metal plates such as chromium, aluminum, zinc and their generatedhydroxideAnd withCapillarityAll of them have good hydrophilic effect.The hydrophilicity of different components is different. The hydrophilicity is protein>starch>cellulose.[1]
Hydrophilic principle
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The property easy to form hydrogen bond with water is called hydrophilicity.Many hydrophilic groups, such as hydroxyl, carboxyl, amino and sulfonic groups, are easily combined with hydrogen bonds, so they are hydrophilic.
Hydrophilicity The property of being wetted by water on the surface of a material.It is an interface phenomenon, and the essence of wetting process is the change of property and energy of material interface.When the cohesion between water molecules is less than the mutual attraction between water molecules and solid material molecules, the material is wetted by water. This kind of material is hydrophilic and is called hydrophilic material;When the cohesion between water molecules is greater than the attraction between water molecules and material molecules, the material surface cannot be wetted by water. This material is hydrophobic (or hydrophobic), which is called hydrophobic material.
Diagram of hydrophilic principle
The interactions between water molecules and the surfaces of different solid materials are different.At the intersection of water (liquid phase), material (solid phase) and air (gas phase), the included angle θ formed along the tangent line of the water drop surface and the contact surface of water and material is called the contact angle (see figure). The θ angle is between 0 ° and 180 °, and the wettability can be estimated from the size of θ angle.The smaller the θ angle, the better the wettability.If θ=0 °, the material is completely wet;θ<90 ° (such as glass, concrete and many mineral surfaces), it is hydrophilic;θ> 90 ° (such as water dropping on the surface of paraffin and asphalt) is hydrophobic;When θ=180 °, it is completely non wetting.[2-3]
Hydrophilic material
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Hydrophilic cotton
Hydrophilic cotton material is a kind of safety and environmental protection material. It has soft hand feel, good support effect, high breathability, good moisture absorption and moisture-proof property, and excellent characteristics of low temperature hardness.[2]
Hydrophilic fiber is a kind of fiber that can absorb water in liquid phase and vapor phase.The hydrophilicity of fibers generally refers to their ability to absorb water.There are two forms of water secreted by human skin surface, namely, gaseous moisture and liquid sweat. Therefore, hydrophilic fibers are traditionally divided into hygroscopic fibers and absorbent fibers according to the mechanism.The absorption capacity of the fiber for gaseous water is called hygroscopicity. The hygroscopicity of the fiber mainly depends on the chemical structure of the fiber, that is, the polarity and number of hydrophilic groups on the fiber macromolecular chain, which can be expressed by the hygroscopicity. Synthetic fibers with this capacity are called hygroscopicity synthetic fibers.The absorption ability of fiber to liquid water is called water absorption. For synthetic fiber, the strength of water absorption mainly depends on the physical structure of the fiber, whether there are conductive micropores on the surface and inner layer of the fiber. Synthetic fiber with this ability is called water absorption synthetic fiber, which is generally expressed by water retention rate.[2]
Hydrophilic leather
If the number of free radicals on the leather surface is equal to the number of fatliquoring agent molecules, the fatliquoring agent molecules will be completely bound to the leather and will not bring hydrophilicity to the leather.The hydrophobic part of the fatliquor is the root of the grease, which can reduce the friction between fibers.If fatliquoring is carried out when the pH value is several units away from the leather isoelectric point, that is, when there are many ionized groups in the leather, the arrangement is different.Fatliquoring agent molecules are no longer parallel to the fiber surface, and ions form a film around the fiber due to electrostatic charges. Although there is no excess grease, it still has the function of lubrication.
When the number of surface fatliquor molecules exceeds the number of formed salt molecules fixed on the fiber, they can be fixed by hydrogen bonding between the hydrogen atom on the hydrophobic chain and the fiber, or the hydrophobic parts can be combined with each other.This frees hydrophilic groups.Hydrophilic groups attract water molecules to make leather fibers hydrophilic.If YinIonic compoundIf there are too many grease molecules, the possibility of interconnecting with each other will remain unchanged, which will expand the hydration area and make leather have great hydrophilicity.[4]
