Oleophilic Oleophobic

Properties related to the surface chemistry or surface area are hydrophilic/ hydrophobic wettability, oleophilic/oleophobic, soil repeUence, water penetration, aesthetics, antibacterial function and friction behaviour. 

Oleophilic/oleophobic fluorinated surfactants without a hydrophile, designed for use in hydrocarbon systems, are in a structural sense also nonionic fluorinated surfactants (see Section 1.8) for example, the semifluorinated alkanes [266-270], block polyethylene-polypropylene glycol ethers prepared with perfluoroalkene trimers [271], surfactants featuring an oligo(hexafluoropropene oxide) chain [272], and carboxamides and sulfonamides derived from A -(perfluorooctanesul-fonyl)piperazine [273]. 

Keywords Hydrophilicity Hydrophobicity Definitions Terminologies Oleophilicity Oleophobicity Superhydrophobicity Superoleophobicity Liquid cohesion Wetting interaction Amphiphobicity Omniphobicity... 

This methodology has been extended to define oleophilicity/oleophobicity for hexadecane. A surface can be defined as oleophilic when its hexadecane Or is <124° and oleophobic when the hexadecane Or is >124°. The finding clearly demonstrates the incorrect presumption that the 90° cutoff is universal for all liquids. Essentially, the philicity/phobicity cutoff is dependent of the surface tension of the liquid, the lower the surface tension, the larger the Or cutoff. 

In the former class, the photopolymerised coating is a hard residue on the developed plate and the polymerised material is usually oleophillic and hydro-phobic. The background (usually a metal substrate) in contrast is usually hydrophillic and oleophobic. In actual practice, the background metal lands are periodically desensitized with a suspension of colloidal particles in an acidic medium. 

Two different liquids may compete with each other, if each of them individually wets a solid surface. In this case the resulting contact angle corresponds to that of a better wetting liquid with nature similar to that of the solid surface. If the surface is better wetted by water than by a hydrocarbon ( 0<9O°), it is referred to as hydrophilic (oleophobic) in the case when the surface is better wetted by non-polar hydrocarbon (0>9O°), it is referred to as hydrophobic (oleophilic). For selective wetting, as opposed to wetting in air, the contact angle, 0, can assume any value between 0° and 180°. When 0 = 0°, the more polar liquid spreads over the solid surface, forcing the less polar liquid away when 0 = 180° the situation is opposite the non-polar liquid phase completely forces the polar liquid away from the solid surface. 

A quantitative characteristic of the energetics of wetting and of the nature of a solid surface (its hydrophilicity and hydrophobicity, oleophilicity and oleophobicity), particularly important for finely porous materials and... 

The reason for this behaviour is that the surfactant molecule contains two structurally distinct parts, one of which is hydrophilic while the other is hydrophobic. Oil-soluble surfactants have an oleophilic and an oleophobic part. In the great majority of surfactants, the hydrophobic part is a hydrocarbon chain, which usually has an average length of 12 to 18 carbon atoms and may include an aromatic ring. A single molecule in aqueous solution seeks the surface, because its hydrocarbon tail is repelled by the water, and it tends to remain there, with the hydrophobic part above the surface and the hydrophilic part below, i.e. in the water phase. Further molecules seek the surface or the walls of the vessel until both are full, at which point further additions result in the formation of micelles, which are clusters of molecules arranged with the hydrophobic parts towards the centre and the hydrophilic parts on the outside. 

When a three-phase contact line is formed by a solid phase and two liquid phases, a selective wetting of the solid phase by one of the liquids takes place. Usually, there is competition between the polar phase (e.g., water) and the nonpolar phase (e.g., hydrocarbon or oil ) in the wetting of the polar and nonpolar solid surfaces. By convention, in selective wetting, the contact angle, 0, is measured into the more polar phase. The solid surface is referred to as hydrophilic ( oleophobic ) when it is predominantly wet by water (0 < 90°), and hydrophobic ( oleophilic ) when it is predominantly wet by a nonpolar liquid (0 > 90°), as illustrated in Figure 1.8. 

FIGURE 1.8 Interface between two liquids and a gas (a) linear tension, ae, (b) selective wetting 0 > 90°, hydrophilic (oleophobic) surface 0 > 90°, hydrophobic (oleophilic) surface (c). 

It is well known that surface-active substances enter into the composition of petroleum, and that these are capable of collecting on the paraffin particles [268], imparting oleophilic properties to these. In this case, the oleophobization of the coatings will not lead to the desired results. 

Nonionic surfactants—do not dissociate into ions, for example, C7Fi5CH2CH20(CH2CH20) H. a special class of nonionic fluorinated surfactants are compounds which do not have a hydrophile but consist of an oleophobic (fluorinated) segment and a oleophilic segment (see Section 1.8). 

The method selected for the preparation of a nonionic fluorinated surfactant depends on the hydrophile, which can be either an polyalkyl ether chain or a polyhydroxy group. Because oxyethylation results in a mixture of oligomers, special methods have been devised for the preparation of monodisperse surfactants. A unique group of nonionic surfactants are amphiphiles without a hydrophile. Semi-fluorinated alkanes with an oleophilic and an oleophobic segment function as nonionic surfactants in oleophilic solvents (see Section 1.8). 

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