In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water. In contrast, hydrophiles are attracted to water.
Waterproofing is the process of making an object, person or structure waterproof or water-resistant so that it remains relatively unaffected by water or resisting the ingress of water under specified conditions. Such items may be used in wet environments or underwater to specified depths.
The lotus effect refers to self-cleaning properties that are a result of ultrahydrophobicity as exhibited by the leaves of Nelumbo, the lotus flower. Dirt particles are picked up by water droplets due to the micro- and nanoscopic architecture on the surface, which minimizes the droplet's adhesion to that surface. Ultrahydrophobicity and self-cleaning properties are also found in other plants, such as Tropaeolum (nasturtium), Opuntia, Alchemilla, cane, and also on the wings of certain insects.
Cassie's law, or the Cassie equation, describes the effective contact angle θc for a liquid on a chemically heterogeneous surface, i.e. the surface of a composite material consisting of different chemistries, that is, non-uniform throughout. Contact angles are important as they quantify a surface's wettability, the nature of solid-fluid intermolecular interactions. Cassie's law is reserved for when a liquid completely covers both smooth and rough heterogeneous surfaces.
Durable water repellent, or DWR, is a coating added to fabrics at the factory to make them water-resistant (hydrophobic). Most factory-applied treatments are fluoropolymer based; these applications are quite thin and not always effective. Durable water repellents are commonly used in conjunction with waterproof breathable fabrics such as Gore-Tex to prevent the outer layer of fabric from becoming saturated with water. This saturation, called 'wetting out,' can reduce the garment's breathability and let water through. As the DWR wears off over time, re-treatment is recommended when necessary. Many spray-on and wash-in products for treatment of non-waterproof garments and re-treatment of proofed garments losing their water-repellency are available.
In chemistry and materials science, ultrahydrophobic surfaces are highly hydrophobic, i.e., extremely difficult to wet. The contact angles of a water droplet on an ultrahydrophobic material exceed 150°. This is also referred to as the lotus effect, after the superhydrophobic leaves of the lotus plant. A droplet striking these kinds of surfaces can fully rebound like an elastic ball. Interactions of bouncing drops can be further reduced using special superhydrophobic surfaces that promote symmetry breaking, pancake bouncing or waterbowl bouncing.
Nanofabrics are textiles engineered with small particles that give ordinary materials advantageous properties such as superhydrophobicity, odor and moisture elimination, increased elasticity and strength, and bacterial resistance. Depending on the desired property, a nanofabric is either constructed from nanoscopic fibers called nanofibers, or is formed by applying a solution containing nanoparticles to a regular fabric. Nanofabrics research is an interdisciplinary effort involving bioengineering, molecular chemistry, physics, electrical engineering, computer science, and systems engineering. Applications of nanofabrics have the potential to revolutionize textile manufacturing and areas of medicine such as drug delivery and tissue engineering.
Nanotechnology is impacting the field of consumer goods, several products that incorporate nanomaterials are already in a variety of items; many of which people do not even realize contain nanoparticles, products with novel functions ranging from easy-to-clean to scratch-resistant. Examples of that car bumpers are made lighter, clothing is more stain repellant, sunscreen is more radiation resistant, synthetic bones are stronger, cell phone screens are lighter weight, glass packaging for drinks leads to a longer shelf-life, and balls for various sports are made more durable. Using nanotech, in the mid-term modern textiles will become "smart", through embedded "wearable electronics", such novel products have also a promising potential especially in the field of cosmetics, and has numerous potential applications in heavy industry. Nanotechnology is predicted to be a main driver of technology and business in this century and holds the promise of higher performance materials, intelligent systems and new production methods with significant impact for all aspects of society.
Water-repellent glass (WRG) is a transparent coating film fabricated onto glass, enabling the glass to exhibit hydrophobicity and durability. WRGs are often manufactured out of materials including derivatives from per- and polyfluoroalkyl substances (PFAS), tetraethylorthosilicate (TEOS), polydimethylsilicone (PDMS), and fluorocarbons. In order to prepare WRGs, sol-gel processes involving dual-layer enrichments of large size glasses are commonly implemented.
Silanization is the attachment of an organosilyl group to some chemical species. Almost always, silanization is the conversion of a silanol-terminated surface to a alkylsiloxy-terminated surface. This conversion confers hydrophobicity to a previously hydrophilic surface. This process is often used to modify the surface properties of glass, silicon, alumina, quartz, and metal oxide substrates, which all have an abundance of hydroxyl groups. Silanization differs from silylation, which usually refers to attachment of organosilicon groups to molecular substrates.
A non-stick surface is engineered to reduce the ability of other materials to stick to it. Non-stick cookware is a common application, where the non-stick coating allows food to brown without sticking to the pan. Non-stick is often used to refer to surfaces coated with polytetrafluoroethylene (PTFE), a well-known brand of which is Teflon. In the twenty-first century, other coatings have been marketed as non-stick, such as anodized aluminium, silica, enameled cast iron, and seasoned cookware.
Janus particles are special types of nanoparticles or microparticles whose surfaces have two or more distinct physical properties. This unique surface of Janus particles allows two different types of chemistry to occur on the same particle. The simplest case of a Janus particle is achieved by dividing the particle into two distinct parts, each of them either made of a different material, or bearing different functional groups. For example, a Janus particle may have one half of its surface composed of hydrophilic groups and the other half hydrophobic groups, the particles might have two surfaces of different color, fluorescence, or magnetic properties. This gives these particles unique properties related to their asymmetric structure and/or functionalization.
Hydrophobic silica is a form of silicon dioxide that has hydrophobic groups chemically bonded to the surface. The hydrophobic groups are normally alkyl or polydimethylsiloxane chains. Hydrophobic silica can be processed in different ways; such as fumed silica, precipitated silica, and aerosol assisted self assembly, all existing in the form of nanoparticles.
An anti-graffiti coating is a coating that prevents graffiti paint from bonding to surfaces.
An antimicrobial surface is coated by an antimicrobial agent that inhibits the ability of microorganisms to grow on the surface of a material. Such surfaces are becoming more widely investigated for possible use in various settings including clinics, industry, and even the home. The most common and most important use of antimicrobial coatings has been in the healthcare setting for sterilization of medical devices to prevent hospital associated infections, which have accounted for almost 100,000 deaths in the United States. In addition to medical devices, linens and clothing can provide a suitable environment for many bacteria, fungi, and viruses to grow when in contact with the human body which allows for the transmission of infectious disease.
The Stöber process is a chemical process used to prepare silica particles of controllable and uniform size for applications in materials science. It was pioneering when it was reported by Werner Stöber and his team in 1968, and remains today the most widely used wet chemistry synthetic approach to silica nanoparticles. It is an example of a sol-gel process wherein a molecular precursor is first reacted with water in an alcoholic solution, the resulting molecules then joining together to build larger structures. The reaction produces silica particles with diameters ranging from 50 to 2000 nm, depending on conditions. The process has been actively researched since its discovery, including efforts to understand its kinetics and mechanism – a particle aggregation model was found to be a better fit for the experimental data than the initially hypothesized LaMer model. The newly acquired understanding has enabled researchers to exert a high degree of control over particle size and distribution and to fine-tune the physical properties of the resulting material in order to suit intended applications.
The Salvinia effect describes the permanent stabilization of an air layer upon a hierarchically structured surface submerged in water. Based on biological models, biomimetic Salvinia-surfaces are used as drag reducing coatings (up to 30% reduction were previously measured on the first prototypes. When applied to a ship hull, the coating would allow the boat to float on an air-layer, reducing energy consumption and emissions. Such surfaces require an extremely water repellent super-hydrophobic surface and an elastic hairy structure in the millimeter range to entrap air while submerged. The Salvinia effect was discovered by the biologist and botanist Wilhelm Barthlott and his colleagues and has been investigated on several plants and animals since 2002. Publications and patents were published between 2006 and 2016. The best biological models are the floating ferns with highly sophisticated hierarchically structured hairy surfaces, and the back swimmers with a complex double structure of hairs and microvilli. Three of the ten known Salvinia species show a paradoxical chemical heterogeneity: hydrophilic hair tips, in addition to the super-hydrophobic plant surface, further stabilizing the air layer.
Shives, also known as shoves, boon or hurd, are the wooden refuse removed during processing flax, hemp, or jute, as opposed to the fibres (tow). Shives consist of "the woody inner portion of the hemp stalk, broken into pieces and separated from the fiber in the processes of breaking and scutching" and "correspond to the shives in flax, but are coarser and usually softer in texture". Shives are a by-product of fiber production.
Self-cleaning surfaces are a class of materials with the inherent ability to remove any debris or bacteria from their surfaces in a variety of ways. The self-cleaning functionality of these surfaces are commonly inspired by natural phenomena observed in lotus leaves, gecko feet, and water striders to name a few. The majority of self-cleaning surfaces can be placed into three categories:
- superhydrophobic
- superhydrophilic
- photocatalytic.
The liquid entry pressure (LEP) of a hydrophobic membrane is the pressure that must be applied to a dry membrane so that the liquid penetrates inside the membrane. LEP with the application in membrane distillation or pervaporation can be calculated as a first parameter to indicate how wettable a membrane is toward different liquid solutions.
