Organophilic surface

Talc is a soft, impalpable, crystalline powder which is odorless and tasteless. Its specific gravity is reported as 2.6-2.8 [4], It is rated as one of the softest materials available, with a hardness of 1-1.5 on the Mohs Mineralogical Scale [5]. It is characterized by hydrophobic-organophilic surface properties and a slippery feel. The amount of softness and slip depend on the source of the talc material. 

Hydrophilic surfaces include those permanent>chaige clays and other minerals that are hydroxylated at their surfaces (iron oxides, kaolinite, etc.). Hydrophobic (organophilic) surfaces include 2 1 silicates with little or no permanent charge (e.g., talc), and components of humus. 

A still more stable organophilic surface on silica particles is obtained by reacting the surface with alkyl chlorosilanes, thus attaching organosilyl groups. For example, the surface of colloidal silica was covered with trimethylsilyl groups by Her (460), who transferred silica from water to triethyl phosphate, dried the sol, added trimethyl-chlorosilane, then heated and removed excess reagent and solvent by vacuum evaporation. The solid product was dispersible to form sols in benzene, ether, and chloroform, but not in water. 

Figure 5.25. Surfaces of single particles, large aggregates, and small aggregates, each shown as hydrophilic, partly organophilic, and completely organophilic (before milling). Hydrophilic surface — thin lines organophilic surface—heavy lines bare, hydrophilic spots after mill ing—wavy lines.

Clays.—The adsorption properties of clays have been extensively studied in the past and the situation up to 1976 is dealt with in van Olphen s book. A major feature of recent work has been the study of the effect on their adsorption characteristics of modification of clays by exchangeable organic cations. The earlier work of Dekany and his collaborators, outlined in a previous Report (Vol. 3, p. 147) and a publication in Hungarian, has been continued. They have been concerned mainly with the adsorption of benzene + alkane and benzene + alcohol mixtures on montmorillonites and kaolinites treated to varying extents with hexadecylpyridinium chloride (HDPCl) to form HDP-complexes of known HDP-content and having a partially organophilic surface. 

Amorphous silicates are produced by destabilization of soluble siUcates to yield amorphous discrete particles in varying degrees of aggregation. The high specific surface area in combination with an organophilic surface is responsible for the excellent ink adsorption characteristics. Amorphous silicate also has the potential to increase somewhat the bulk of the paper sheet. 

Recently, Mark and co-workers also reported on organophilic silica formed by the combination of the sol-gel procedure and water-in-oil micro-emulsion method, in which methacryloyloxypropyltrimethoxysilane was used as one component of silica matrix [8]. The size of the silica particle was controlled by the content of water and emulsifier used. The surface of the particles was effectively covered with methacryloyl. organic groups. This organophilic silica is expected to be used as a novel component of composite materials. 

Bentonite is an impure clay that is formed by weathering of volcanic tuffs. It contains a high content of montmorillonite. Bentonites exhibit properties such as ability to swell, ion exchange, and thixotropy. Properties can be modified by ion exchange, for example, exchange of earth alkali metals to alkali metals. The specific surface can be modified with acid treatment. Organophilic properties can be increased by treatment with quaternary ammonia compounds. 

Layered phosphate/phosphonate and phosphonate materials, obtained by substitution of the phosphate moiety by phosphonate groups, display interesting tunable hydrophilic/organophilic properties for adsorption processes. When Candida rugosa lipase (CRL) is simply equilibrated with zirconium phosphate and phosphonate [135,136], immobilization was demonstrated to take place at the surface of the microcrystals. However, because lipase exhibits a strong hydrophobic character, its uptake by zirconium phosphate and phosphonate was much more related to the hydrophobic/hydrophilic character of the supports than to the surface area properties. A higher uptake is observed for zirconium-phenylphosphonate (78 %)... 

The ZnO surface is made more organophilic by coating it with oil and propionic acid. The ZnO is often deaerated and sometimes pelletized or granulated to improve handling properties. 

A hydrated metal ion (Mz+) will always prefer the aqueous phase to the organic phase. To get the metal ion to extract, some or all of the inner hydration sphere must be removed. The resulting complex must be electrically neutral and organophilic, that is, have an organic surface that interacts with the organic solvent. This can be done by ... 

Mass-transport limitations are common to all processes involving mass transfer at interfaces, and membranes are not an exception. This problem can be extremely important both for situations where the transport of solvent through the membrane is faster and preferential when compared with the transport of solute(s) - which happens with membrane filtration processes such as microfiltration and ultrafiltration - as well as with processes where the flux of solute(s) is preferential, as happens in organophilic pervaporation. In the first case, the concentration of solute builds up near the membrane interface, while in the second case a depletion of solute occurs. In both situations the performance of the system is affected negatively (1) solute accumulation leads, ultimately, to a loss of selectivity for solute rejection, promotes conditions for membrane fouling and local increase of osmotic pressure difference, which impacts on solvent flux (2) solute depletion at the membrane surface diminishes the driving force for solute transport, which impacts on solute flux and, ultimately, on the overall process selectivity towards the transport of that specific solute. 

Activated carbon is by far the most widely used adsorbent. It is available in a wide range of different forms that differ mainly in pore size and pore size distribution. The carbon surface is essentially nonpolar although some polarity can be imparted by surface oxidation or other pre-treatments. It is widely used for removal of low concentrations of organics, either from aqueous streams (for example, decolorization of sugar or water treatment) or from vapor streams (for example, in range hoods and other pollution-control devices). Crystalline silica adsorbents such as silicalite are also organophilic but are substantially more expensive than activated carbon so their application is generally limited to situations where, for some reason, the use of carbon is not appropriate. 

The specific activity of Ti-sites in oxidation with aqueous H202 was shown to decrease from microporous to mesoporous molecular sieves such as MCM-41 and HMS. The surface hydrophilicity of the latter mesoporous silicates is likely one of the main reasons for the low activity of Ti sites.[47] Water molecules adsorbed on the surface silanol groups would limit the access of organophilic reagents to the Ti sites.1751 This can be limited, to a certain extent, by grafting hydrophobic groups on the surface silanols.1761... 

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