Inherent hydrophobicity

Water Uptake. There is evidence to suggest that water uptake caused by capillary forces is the crucial factor in the disintegration process of many formulations. In such systems the pore structure of the tablet is of prime importance and any inherent hydrophobicity of the tablet mass will adversely affect it. Therefore, disintegrants in this group must be able to maintain a porous structure in the compressed tablet and show a low interfacial tension towards aqueous fluids. Rapid penetration by water throughout the entire tablet matrix to facilitate its breakup is thus achieved. Concentrations of disintegrant that ensure a continuous matrix of disintegrant are desirable and levels of between 5 and 20% are common. 

The inherent hydrophobicity once thought to be typical of sulphides (Ravitz and Porter, 1933) is now thought to be restricted to sulphides such as molybdenite (Chander et al., 1975) and other minerals or compound with special structural feature (Gaudin et al, 1957b). Common commercial sulphide minerals, which are needed to recover in flotation, are normally composed of anion (S ) and heavy metal ions such as Cu, Cu, Pb, Zn, Hg, Sb, Bi transitive metal ion such as Fe, Co, Ni and noble and rare metal ions such as Ag, Au, Mo. On the basis of structural pattern or mode of linkage of the atoms or polyhedral imits in space, Povarennyk (1972) introduced a crystallochemical classification of sulphide minerals, which have six major patterns as shown in Table 1.1. 

Heyes and Trahar (1984) leached pyrite with cyclohexane and compared the extract with a sulphur-containing solution of cyclohexane in a UV spectra photometer as shown in Fig. 1.4, indicating that sulphur was present at the mineral surface. Therefore, the inherent hydrophobicity and natural floatability once thought to be typical of sulphides is now thought to be restricted to sulphides such as molybdenite and other minerals or compound with special structural features. The collectorless floatability that most sulphide minerals showed came from the self-induced or sulphur-induced flotation at certain pulp potential range and certain conditions. 

Kartio, I. J., Basilio, C. I., Yoon, R. H., 1996. An XPS study of sphalerite activation by copper. In R. Woods, F. Doyle, P. E. Richardson (eds.), Electrochemistry in Mineral and Metal Processing IV. The Electro-Chemical Society, 25 - 34 Kelebek, S., 1987. Wetting behaviow, polar characteristics and flotation of inherently hydrophobic minerals. Trans. MM, Sec. C, 96 103 - 107... 

The most common material used is cellophane, which is a cellulose film, which acts as a membrane and is capable of resisting zinc penetration. The cycle life of cells utilizing this material is severely limited due to the hydrolysis of the cellophane in alkaline solution. Various methods have been tried to stabilize cellulose materials, such as chemical treatment and radiation grafting to other polymers, but none have, as of now proved economically feasible. The most successful zinc migration barrier material yet developed for the nickel—zinc battery is Celgard microporous polypropylene film. It is inherently hydrophobic so it is typically treated with a wetting agent for aqueous applications. 

Clearly, changing the Si/Al ratio of a zeolite also changes its cation content the fewer aluminium atoms, the fewer cations will be present to balance the charges. The highly siliceous zeolites are inherently hydrophobic in character, and their affinity is for hydrocarbons. 

As nanotubes are inherently hydrophobic and dextran is a very hydrophilic polymer, it is first necessary to functionalize the dextran with hydrophobic phenoxy moieties.29,30 Increasing the weight percent phenoxy content from 0 to 8 wt% results in the increase of the number of nanotube in solution, where dextran alone is not capable of suspending nanotubes in solution. Again, a gentle dialysis method is used to assemble dextran on the nanotube surface. 

Protein adsorption onto intrinsically repellent materials is enhanced by a brief plasma treatment that chemically and physically alters the surface properties. Stencil-assisted plasma oxidation of inherently hydrophobic polymers (e.g., PDMS... 

The high Si Al ratio of the material, typically around 10, makes the material inherently hydrophobic. Changing the Si Al ratio of the material has, however, a marked influence on the hydrophobicity. The increased hydrophobicity of siliceous Beta has been demonstrated by competitive adsorption of toluene and water. The so-called hydrophobicity index32, the amount of toluene adsorbed divided by the amount of water adsorbed at 25 °C amounts to 1.4 to 2.2 for a Si Al = 10 sample and increases to 10.8 to 66 for the all-silica material (see Table 2). The large difference observed for the all-silica zeolites is most likely due to differences in the amount of defects in the material. These defects are essentially silanol pairs required for template charge compensation during synthesis as shown by van der Waal et al.12... 

Used in conjunction with a monomeric plasticizer and a metal oxide to make an inherently hydrophobic material more hydrophilic. Commonly used in toys and medical equipment. 

The surface of polymers have been knovm to be of Importance in many applications of polymers. Polyorganosiloxanes are industrially produced in large quantity for various purposes depending molecular weight and copolymer composition. The Inherent hydrophobic nature of slloxanes coupled with their ability to accumulate on the surface of polymer blends has allowed the polyorganosiloxanes to be used widely to Impart hydrophoblclty to the surfaces of other materials, particularly in the case of polymers which by themselves are devoid of such properties.(U- )... 

From the above three struetural variants one may infer that the value of 0.03 mole in the eellular lipids strongly indieates the required eoneentration for immobilization of tadpoles . In short, it adequately eonfers the bioactivity of a drug substance to its inherent hydrophobicity and hydrophilicity. 

The cause and effect relation between hydrothermal stability and water permeation is not apparent. This is a point where more attention is necessary in the future studies. It is possible that the larger H2/H2O separation factor or in other words the low permeation of H2O through the membrane is the reason for the better hydrothermal stability of the membranes. Kinetic limitations have indeed shown to enhance the stability of protective coatings and coated materials. On the other hand, it should also be reasoned that the inherent hydrophobic structure of the material is the source of the improvement in hydrothermal stability and for the reduction in H2O permeation by limiting the number of sites where H2O could be adsorbed (as in Fig. 16.7). The results discussed so far clearly indicate that the improvement in hydrothermal stability of the membranes is linked to the improvement in porous structure (structure and quantity of surface exposed to H2O) of the membranes itself. 

The above descriptions show the monomeric structures of starch, dextrin, cellulose, and guar gum. In reality, these polysaccharides can be extracted from different sources and the chain length and configuration, molecular weights, and the contents of impurities may vary considerably. Generally, starches have been used mainly as flocculants or flotation depressants for iron oxide minerals and phosphate minerals while the associated silica is floated. Dextrin has been mainly tested as depressants for inherently hydrophobic minerals such as talc, molybdenite, and coal [96]. Applications of polysaccharides in other mineral systems, both in the laboratory and in commercial processes, have also been frequently reported. As can be seen, the polysaccharides have been used or tested as selective depressants in practically all types of mineral systems, ranging from oxides, sulfides, salt-type, and inherently hydrophobic minerals. 

The properties of synthetic materials are hugely important to the sportswear industry they are inherently hydrophobic, thermoplastic, and demonstrate high-tensile strength, unlike natural and regenerated fibers that are absorbent but not as strong. Key polymer groups such as polyester and polyamide are conventionally synthesized from non-renewable sources at high cost to the environment. Efforts to find alternative... 

The hydrophilicity conferred by the presence of alkoxy groups in the polymeric pendant chains results in an enhancement of the solubility of these polymers (Kim et al. 2003). Thus, the inherent hydrophobicity of mcl-PHAs could be strongly modified by the introduction of hydrophilic moieties into the side chain, increasing their applicability as biocompatible materials for a wide range of biomedical devices. 

As mentioned earlier, flame synthesized carbon nanostructures demonstrate superhydrophobicity due to inherent hydrophobicity of carbon as well as the formation of dual-scale roughness during deposition. However, their main drawback is that nanostructured carbon materials do not form a firm bond with the surface upon which they are assembled, considerably reducing their practical applications in liquid repellent surface... 

In recent years, due to a plethora of potential applications of superhydro-phobicity in daily life, many elforts have been taken to fabricate artificial superhydrophobic surfaces. Depending on the application and material, different methods have been employed to create superhydrophobic smfaces [8], Most of these methods involve either creating a micro/ nano-structme on an inherently hydrophobic material [9,10] or treating a specific micro/nano-structure with a hydrophobic coating [11-14]. For instance, for metallic materials, roughened surfaces have to be coated with low surface energy materials. 

In order to prepare hydrophobic and superhydrophobic surfaces, femtosecond laser was used to pattern the metallic surface and after irradiation the surface was subjected to silanization using dip coating in order to reduce its surface energy and make it inherently hydrophobic. Details on the silanization method used can be found elsewhere [27]. 

The equation was originally derived for the homogeneous solid-liquid interface (no air pockets) (Fig. 6a) using the surface force balance and empirical considerations however, it was later put in a proper thermodynamic framework. It is important that according to Wenzel model the inherently hydrophilic flat surface will be more hydrophilic when rough, and inherently hydrophobic surface will become more hydrophobic. 

It is seen from Eq. (4) that an inherently hydrophobic surface (cos Oq > 0) can turn into a hydrophobic one (cos < 0) in the Cassie regime. 

The most successful zinc migration barrier material yet developed for the nickel-zinc battery is Celgard . This is a microporous polypropylene film which has a typical thickness of 0.025 mm Polypropylene is inherently hydrophobic so the material is typically treated with a wetting agent for aqueous applications. One disadvantage of microporous materials. 

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