Contenido

Las superficies superhidrofóbicas, tales como las hojas de la planta de loto, son aquellas que es extremadamente difícil que se mojen. Los ángulos de contacto de una gota de agua son mayores a 150°.[11]​ Esto se denomina efecto loto, y es una propiedad física relacionada con la tensión de interfase, más que una propiedad química.

Theory

In 1805, Thomas Young defined the contact angle θ by analyzing the forces acting on a drop of fluid that is on a solid surface and surrounded by a gas.[12]​.

where.

θ is measured using a contact angle goniometer.

Wenzel determined that when the liquid is in intimate contact with a microstructured surface, θ changes to θ.

where r is the ratio between the real area and the projected area.[13]​ The Wenzel equation shows that the microstructure of a surface amplifies the natural tendency of a surface. A hydrophobic surface (one that has an original contact angle greater than 90°) is more hydrophobic if it is microstructured – its new contact angle is greater than the original. However, a hydrophilic surface (one that has an original contact angle less than 90°) becomes less hydrophilic if it is microstructured – its new contact angle becomes smaller than the original one.[14]​

Cassie and Baxter that if the liquid is suspended above microstructures, θ is modified to θ:.

where φ is the area fraction of the solid that touches the liquid.[15] Cassie–Baxter liquid state is more mobile than the Wenzel state.

We can predict whether the Wenzel or Cassie-Baxter state should exist by calculating the new contact angle with both equations. By a free energy minimization argument, the relation that predicted the new smallest contact angle is the state most likely to exist. Said in mathematical terms, for the Cassie-Baxter state to exist, the following inequality must be true.[16]​.

A recent alternative criterion for the Cassie-Baxter state states that the Cassie-Baxter state exists when the following 2 criteria are met: 1) The contact line forces exceed the body forces from the weight of the unsupported droplets and 2) The microstructures are tall enough to prevent the liquid bridging the microstructures from touching the base of the microstructures.[17]​.

A new criterion has recently been developed for the switch between the Wenzel and Cassie-Baxter states based on surface roughness and surface energy.[18] The criterion focuses on the ability to trap air under liquid droplets on rough surfaces, which could indicate whether the Wenzel or Cassie-Baxter model should be used for a certain combination of surface roughness and energy.

Contact angle is a measure of static hydrophobicity, and contact angle hysteresis and slip angle are dynamic measures. Contact angle hysteresis is a phenomenon that characterizes surface heterogeneity.[19]​ When a pipette injects a liquid onto a solid, the liquid will form a certain 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 that the droplet had immediately before advancing outward is called the advancing contact angle. The recoil contact angle is now measured by pumping the liquid back out of the droplet. The droplet will decrease in volume, the contact angle will decrease, but its three-phase boundary will remain stationary until it suddenly retreats inward. The contact angle that the drop had immediately before recoiling inward is called the recoil contact angle. The difference between the advancing and receding contact angles is called contact angle hysteresis and can be used to characterize surface heterogeneity, roughness, and mobility.[20]​ Surfaces that are not homogeneous will have domains that prevent contact line movement. Slip angle is another dynamic measure of hydrophobicity and is measured by depositing a droplet on a surface and tilting the surface until the droplet begins to slide. In general, liquids in the Cassie-Baxter state have lower slip angles and contact angle hysteresis than those in the Wenzel state.

Dettre and Johnson discovered in 1964 that the phenomenon of the superhydrophobic lotus effect was related to rough hydrophobic surfaces, and developed a theoretical model based on experiments with paraffin-coated glass beads or TFE telomeres. The self-cleaning property of superhydrophobic micro-nanostructured surfaces was reported in 1977. Perfluoroalkyl, perfluoropolyether, and superhydrophobic materials formed by RF plasma were developed, used for electrowetting, and marketed for biomedical applications between 1986 and 1995.[22][23][24][25] Other technologies and applications have emerged since the mid-1990s.[26] In 2002, a durable hierarchical superhydrophobic composition, applied in one or two steps, was disclosed, comprising nanometer-sized particles ≤ 100 nanometers that were superimposed on a surface with features or micrometer-sized particles ≤ 100 micrometers. It was observed that larger particles protected smaller ones from mechanical abrasion.[27]​.

In recent research, superhydrophobicity has been reported by allowing alkyl ketene dimer "Dimer (chemistry)") (AKD) to solidify into a nanostructured fractal surface.[28] Since then, many works have presented fabrication methods to produce superhydrophobic surfaces, including particle deposition,[29]​ sol-gel techniques,[30]​ plasma treatments,[31]​ steam,[29]​ and casting techniques.[32]​ The current opportunity for research impact lies primarily in fundamental research and practical manufacturing.[33]​ Debates have recently arisen about 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 dot in a rough hydrophobic field, a rough hydrophobic dot in a smooth hydrophobic field, and a hydrophilic dot in a hydrophobic field.[34] Experiments demonstrated that the chemistry and geometry of the surface at the contact line affected the contact angle. and to contact angle hysteresis"), but the surface within the contact line had no effect. The argument has also been proposed that increasing irregularities in the contact line improves droplet mobility.[35]​.

Many hydrophobic materials found in nature are based on Cassie's law and are biphasic "Phase (matter)") at the submicron level with an air component. The lotus effect is based on this principle. Inspired by it, many superhydrophobic functional surfaces have been prepared.[36]​.

An example of a bionic or biomimetic superhydrophobic material in nanotechnology is nanopin film.

In medicine, the term hydrophobia is used as a synonym for rabies. The hydrophobe therefore is the one who suffers from the disease commonly known as rabies or hydrophobia. It is caused by a virus belonging to the Rhabdoviridae family, genus Lyssavirus type 1, typical of certain warm-blooded animals, such as dogs, cats, rats, wolves and bats, but it can be transmitted to humans if bitten by an infected animal.

This virus attacks the central nervous system and, if the disease is not prevented by vaccination, ends up causing the death of the patient. When a person is infected with the rabies virus, the symptoms of the disease can take between 30 and 180 days to appear; The most characteristic are sensory alterations and mobility problems. At first the patient experiences mood changes, unjustified fears, pain in the wound and general discomfort; then he suffers from spasms, excitement, aversion to water because, when swallowing or seeing water, the muscles of the throat become paralyzed, mental disorders and hallucinations; Finally, the paralysis immobilizes his limbs and, when it spreads to the brain and lungs, causes death by not moving.

In the hydrophobic areas of the plate image, water is repelled, and the ink adheres to these areas, since the offset printing system is based on a water-ink balance.

Hydrophobic concrete") has been produced since the middle of the century.

Recent active research on superhydrophobic materials could eventually lead to more industrial applications.

A simple routine of coating cotton fabrics with silica[37]​ or titania[38]​ particles using the sol-gel technique), which protects the fabric from ultraviolet light and makes it superhydrophobic.

An effective routine has been reported to make polyethylene superhydrophobic and therefore self-cleaning.[39]​ 99% of the dirt on such a surface is easily removed.

Patterned superhydrophobic surfaces also show promise for lab-on-a-chip microfluidic devices and can dramatically improve surface-based bioanalysis[40].

In pharmaceutical products, the hydrophobicity of pharmaceutical mixtures affects important quality attributes of the final products, such as drug dissolution and hardness.[41]Methods have been developed to measure the hydrophobicity of pharmaceutical materials.[42][43]​.

The development of hydrophobic surfaces (passive diurnal radiative cooling") (PDRC), whose effectiveness in solar reflectance") and thermal emittance is based on their cleanliness, has improved the "self-cleaning" of these surfaces. In addition, scalable and sustainable hydrophobic PDRCs that avoid VOCs have been developed").[44]​.

Contenido

Las superficies superhidrofóbicas, tales como las hojas de la planta de loto, son aquellas que es extremadamente difícil que se mojen. Los ángulos de contacto de una gota de agua son mayores a 150°.[11]​ Esto se denomina efecto loto, y es una propiedad física relacionada con la tensión de interfase, más que una propiedad química.

Theory

In 1805, Thomas Young defined the contact angle θ by analyzing the forces acting on a drop of fluid that is on a solid surface and surrounded by a gas.[12]​.

where.

θ is measured using a contact angle goniometer.

Wenzel determined that when the liquid is in intimate contact with a microstructured surface, θ changes to θ.

where r is the ratio between the real area and the projected area.[13]​ The Wenzel equation shows that the microstructure of a surface amplifies the natural tendency of a surface. A hydrophobic surface (one that has an original contact angle greater than 90°) is more hydrophobic if it is microstructured – its new contact angle is greater than the original. However, a hydrophilic surface (one that has an original contact angle less than 90°) becomes less hydrophilic if it is microstructured – its new contact angle becomes smaller than the original one.[14]​

Cassie and Baxter that if the liquid is suspended above microstructures, θ is modified to θ:.

where φ is the area fraction of the solid that touches the liquid.[15] Cassie–Baxter liquid state is more mobile than the Wenzel state.

We can predict whether the Wenzel or Cassie-Baxter state should exist by calculating the new contact angle with both equations. By a free energy minimization argument, the relation that predicted the new smallest contact angle is the state most likely to exist. Said in mathematical terms, for the Cassie-Baxter state to exist, the following inequality must be true.[16]​.

A recent alternative criterion for the Cassie-Baxter state states that the Cassie-Baxter state exists when the following 2 criteria are met: 1) The contact line forces exceed the body forces from the weight of the unsupported droplets and 2) The microstructures are tall enough to prevent the liquid bridging the microstructures from touching the base of the microstructures.[17]​.

A new criterion has recently been developed for the switch between the Wenzel and Cassie-Baxter states based on surface roughness and surface energy.[18] The criterion focuses on the ability to trap air under liquid droplets on rough surfaces, which could indicate whether the Wenzel or Cassie-Baxter model should be used for a certain combination of surface roughness and energy.

Contact angle is a measure of static hydrophobicity, and contact angle hysteresis and slip angle are dynamic measures. Contact angle hysteresis is a phenomenon that characterizes surface heterogeneity.[19]​ When a pipette injects a liquid onto a solid, the liquid will form a certain 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 that the droplet had immediately before advancing outward is called the advancing contact angle. The recoil contact angle is now measured by pumping the liquid back out of the droplet. The droplet will decrease in volume, the contact angle will decrease, but its three-phase boundary will remain stationary until it suddenly retreats inward. The contact angle that the drop had immediately before recoiling inward is called the recoil contact angle. The difference between the advancing and receding contact angles is called contact angle hysteresis and can be used to characterize surface heterogeneity, roughness, and mobility.[20]​ Surfaces that are not homogeneous will have domains that prevent contact line movement. Slip angle is another dynamic measure of hydrophobicity and is measured by depositing a droplet on a surface and tilting the surface until the droplet begins to slide. In general, liquids in the Cassie-Baxter state have lower slip angles and contact angle hysteresis than those in the Wenzel state.

Dettre and Johnson discovered in 1964 that the phenomenon of the superhydrophobic lotus effect was related to rough hydrophobic surfaces, and developed a theoretical model based on experiments with paraffin-coated glass beads or TFE telomeres. The self-cleaning property of superhydrophobic micro-nanostructured surfaces was reported in 1977. Perfluoroalkyl, perfluoropolyether, and superhydrophobic materials formed by RF plasma were developed, used for electrowetting, and marketed for biomedical applications between 1986 and 1995.[22][23][24][25] Other technologies and applications have emerged since the mid-1990s.[26] In 2002, a durable hierarchical superhydrophobic composition, applied in one or two steps, was disclosed, comprising nanometer-sized particles ≤ 100 nanometers that were superimposed on a surface with features or micrometer-sized particles ≤ 100 micrometers. It was observed that larger particles protected smaller ones from mechanical abrasion.[27]​.

In recent research, superhydrophobicity has been reported by allowing alkyl ketene dimer "Dimer (chemistry)") (AKD) to solidify into a nanostructured fractal surface.[28] Since then, many works have presented fabrication methods to produce superhydrophobic surfaces, including particle deposition,[29]​ sol-gel techniques,[30]​ plasma treatments,[31]​ steam,[29]​ and casting techniques.[32]​ The current opportunity for research impact lies primarily in fundamental research and practical manufacturing.[33]​ Debates have recently arisen about 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 dot in a rough hydrophobic field, a rough hydrophobic dot in a smooth hydrophobic field, and a hydrophilic dot in a hydrophobic field.[34] Experiments demonstrated that the chemistry and geometry of the surface at the contact line affected the contact angle. and to contact angle hysteresis"), but the surface within the contact line had no effect. The argument has also been proposed that increasing irregularities in the contact line improves droplet mobility.[35]​.

Many hydrophobic materials found in nature are based on Cassie's law and are biphasic "Phase (matter)") at the submicron level with an air component. The lotus effect is based on this principle. Inspired by it, many superhydrophobic functional surfaces have been prepared.[36]​.

An example of a bionic or biomimetic superhydrophobic material in nanotechnology is nanopin film.

In medicine, the term hydrophobia is used as a synonym for rabies. The hydrophobe therefore is the one who suffers from the disease commonly known as rabies or hydrophobia. It is caused by a virus belonging to the Rhabdoviridae family, genus Lyssavirus type 1, typical of certain warm-blooded animals, such as dogs, cats, rats, wolves and bats, but it can be transmitted to humans if bitten by an infected animal.

This virus attacks the central nervous system and, if the disease is not prevented by vaccination, ends up causing the death of the patient. When a person is infected with the rabies virus, the symptoms of the disease can take between 30 and 180 days to appear; The most characteristic are sensory alterations and mobility problems. At first the patient experiences mood changes, unjustified fears, pain in the wound and general discomfort; then he suffers from spasms, excitement, aversion to water because, when swallowing or seeing water, the muscles of the throat become paralyzed, mental disorders and hallucinations; Finally, the paralysis immobilizes his limbs and, when it spreads to the brain and lungs, causes death by not moving.

In the hydrophobic areas of the plate image, water is repelled, and the ink adheres to these areas, since the offset printing system is based on a water-ink balance.

Hydrophobic concrete") has been produced since the middle of the century.

Recent active research on superhydrophobic materials could eventually lead to more industrial applications.

A simple routine of coating cotton fabrics with silica[37]​ or titania[38]​ particles using the sol-gel technique), which protects the fabric from ultraviolet light and makes it superhydrophobic.

An effective routine has been reported to make polyethylene superhydrophobic and therefore self-cleaning.[39]​ 99% of the dirt on such a surface is easily removed.

Patterned superhydrophobic surfaces also show promise for lab-on-a-chip microfluidic devices and can dramatically improve surface-based bioanalysis[40].

In pharmaceutical products, the hydrophobicity of pharmaceutical mixtures affects important quality attributes of the final products, such as drug dissolution and hardness.[41]Methods have been developed to measure the hydrophobicity of pharmaceutical materials.[42][43]​.

The development of hydrophobic surfaces (passive diurnal radiative cooling") (PDRC), whose effectiveness in solar reflectance") and thermal emittance is based on their cleanliness, has improved the "self-cleaning" of these surfaces. In addition, scalable and sustainable hydrophobic PDRCs that avoid VOCs have been developed").[44]​.