Hydrophobic particles

For more efficient deinking, flotation must be used. This is considerably more complex, and the mechanism by which it works is still somewhat speculative. It is necessary to make the detached ink particle hydrophobic so that it can adhere to an air bubble and be removed by flotation. For this to happen, it appears to be necessary for the particles to be in the size range 10—150 jum. The processs consists of a cell or tank with a high speed agitator to induce a partial vacuum which causes air to enter the system in the form of small air bubbles, these carry the ink particles to the surface. 

Hydrophobic interaction chromatography (HIC) is a column chromatography technique which can determine particle hydrophobicity by interaction with a hydrophobic gel matrix [142,149,150]. Hydrophilic particles pass through the column without interaction, whereas particles with increased hydrophobicity show a retarded elution and are retained by the column. Hydrophobicity measurements are used to determine the hydrophobicity of nanoparticulate carriers and correlate this to their in vivo biodistribution [10, 149]. 

In carrier flotation, small-sized (several pm diameter) particles become attached to the surfaces of larger particles (perhaps 50 pm diameter, the carrier particles) [630]. The carrier particles attach to the air bubbles and the combined aggregates of small desired particles, carrier particles, and air bubbles float to form the froth. An example is the use of limestone particles as carriers in the flotation removal of fine iron and titanium oxide mineral impurities from kaolinite clays [630]. The use of a fatty acid collector makes the impurity oxide particles hydrophobic these then aggregate on the carrier particles. In a sense, the opposite of carrier flotation is slime coating, in which the flotation of coarse particles is decreased or prevented by coating their surfaces with fine hydrophilic particles (slimes). An example is the slime coating of fine fluorite particles onto galena particles [630],... 

The particles of cyclodextrin-grafted silicone are also the vehicles for the transport of the active substance to the site of its therapeutic action. In the case of anti-fnngal dosage form for topical administration action, penetration and slow release in the skin is searched for [21-23]. The stratum corneum top layer is made of cor-neocytes separated by a lipidic intercellular medium. Internal layers, epidermis and dermis are essentially aqueous media. The top layer is hydrophobic whereas the internal layers are hydrophilic. The penetration into the skin is controlled by the hydrophobic character of the particles. Hydrophobic materials easily penetrate and possibly accumulate in the stratum corneum. A slow release of the drug into the deep hydrophilic layers is possible from this medium. Silicone emulsions are often selected for cosmetic formulations because of the favorable spreading of silicone oils at the skin surface together with their low-irritancy properties. 

In some flotation deinking, calcium chloride is used with a long-chain fatty acid to make the ink particles hydrophobic.31... 

Fig. 11.10. Number of quartz particles collected by one bubble of 2 mm diameter in water at different degrees of particle hydrophobicity 0 = 20 (B), 0 = 50°( ), 0 = 65 (A), 0 = 88°(V) the solid line represents the number of collisions per bubble calculated from collision efficiency for attachment during the first collision with a retarded surface (—.) and during the second collision with an unretarded surface (+ +)...

Most applications of liquid column chromatography are now made on silica which has been chemically modified (bonded phase chromatography). The modification is made by chemical reaction between the silanol groups and a chlorosilane compound. The carbon radicals of the chlorosilane compound determines the nature of the final column material. Using silanes containing alkyl carbon chains with 8-22 carbon atoms gives the particles hydrophobic surfaces, but more polar surfaces may be obtained by incorporation of alcohol, amino, cyano or other groups in the alkyl chain. 

Other inorganic nanoparticles have been encapsulated with miniemulsion polymerization, and a hydrophobilizing agent was used to render the particles hydrophobic prior to minianulsification. For example, calcium carbonate was pretreated with stearic acid prior to being dispersed into the monomer phase. Alumina and magnetite were pretreated with oleic acid, laponite was pretreated with a cetyltrimethylammonium bromide, and silica was pretreated with cetyltrimethyl-ammonium chloride" or methacryloxy(propyl)trimethoxysilane. ... 

One of the most widely used magnetic beads was prepared by Ugelstad et al. [100]. In the preparation of magnetic polymer particles, hydrophobic polymers of styrene (St) or styrene-co-divinylbenzene (St-co-DVB) are used, which have a large... 

Bubble pickup-. A bubble is formed at the tip of a capillary tube and introduced into a stirred suspension of particles. Hydrophobic particles will adhere to the bubble. Under standardized conditions, the amount of material collected on the bubble(s) can be compared with other suspensions. Microflotation-. Any small-scale flotation cell device can be used to contact a suspension with rising air bubbles onto which hydrophobic particles will become attached. The particle-laden froth that is produced either flows to a collection tube (as in HaUimond or similar type flotation tubes) or can be drawn off into a separate collection vessel (as in small-scale Denver, levitation device or similar type flotation cells). This is also referred to as a levitation technique. 

For adsorption of a cationic surfactant on a colloidal particle, the particle must be at least of a certain minimum size, as pointed out by Matijevi6 and Ottewill (297). When there is only sufficient surfactant present to render the surface of the colloidal particles hydrophobic, coagulation occurs but when more is added to form a second layer owing to van der Waals attraction between the hydrocarbon chains, the ionized groups of the second layer are then oriented toward the solution, and the particles are separated and peptized with a reversed surface charge. 

The silica nanoparticles of about 40-nm diameter were produced by the Stober method [9] from ethanol, ammonium hydroxide and tetraethyl orthosilicate. One kind of sample was used as formed, (hydrophiUc sample), the other was surface-treated by trimethyl-silyl-A,A-dimethylcarbamate, in order to render the particles hydrophobic. The samples were used from the alcosols. The solid content of the sols was determined from the amount of solid residuum after evaporating the solvent at 80 °C. The diameter of the particles was determined from the transmission electron microscope (TEM) image of layers transferred on Formvar-coated grids. Details of sample preparation and characterization have been described in previous papers [10, 11]. 

Flotation is a method of separating solids Irom streams by creating a froth to which they are attracted. Thus in a slurry circuit, flocculants are added to create a froth rich with the metal concentrate. The trick is to make mineral particles hydrophobic, or water repellant. Flotation involves the selected adsorption of hydrocarbons (e.g., ethyl xanthate) on liberated minerals (e.g., chalcopyrite), which can then be attached to and transported by air bubbles in the slurry to a so-called froth layer and then separated from the hydrophilic (wetted) particles. 

A standalone and particularly important example of rendering particles hydrophobic is encountered in ore enrichment. A crushed ore containing a mixture of useful minerals and barren rock undergoes the process of froth flotation, in which it is exposed to an aqueous surfactant solution. The surfactants used in this process are capable of selectively oiling only one of these fractions (typically desired mineral particles). Upon bubbling the suspension with air, hydrophobized particles, such as particles of metal sulfides, are attached to the hydrophobic air bubbles and are carried to the surface with the froth, while the particles of barren rock (such as sulfates or quartz) undergo settling at the bottom. 

There is some evidence that this deactivation is apparent with other hydrophobic particle-hydrophobic oil mixed antifoams [8-10]. It also seems probable that the prolongation of antifoam effectiveness accompanying increase in viscosity of the oil [2, 3] concerns the effect of that increase on the process of antifoam deactivation rather than on the intrinsic effectiveness of the antifoam. Moreover, partial deactivation of antifoams during dispersal to form pulsions appears to result from the same cause as deactivation during foam generation [6]. This deactivation is commercially important because antifoam products for certain applications are often necessarily prepared as emulsions. 

The predictions of DLVO theory describe the behavior of a simplified colloidal solution and should predict if a colloid will aggregate or remain suspended in a given solvent however, in real systems this simplified model is not often accurate. For example, these models do account for the effects of steric interactions between particles or excluded volume effects. These effects are discussed in the following sections. Other factors not considered include the effects of water structure, particle hydrophobicity, and any specific ionic arrangements around the particles. DLVO theory is a good starting point to think about the behavior of colloidal solutions. 

The bare silica particles in buffer solution have a f -potential of about —35 mV. Around a -potential of —25 mV, flocculation of particles is observed for all carbon chain lengths. The other way around, a value of the C -potential of —25 mV does not mean automatically flocculation. For instance in presence of multivalent salt but in absence of amphiphiles no flocculation was observed. This means that electrostatic repulsion is not the main reason for flocculation but hydrophobic interactions. Due to cooperative binding of amphiphiles at the Silica particles hydrophobic patches are formed at the particles which drive the flocculation. This assumption is supported by the fact that the alkylamine concentration for... 

In a system consisting of poly(methyl methaoylate) (PMMA) and silica particles hydrophobized with cetyltrimethylammonium chloride (CTMA-Cl), desorption of the surfactant leads to a decrease of surface hydrophobidty, which prohibits the integration of the silica particles into the polymer matrix [19]. To overcome this problem, the interaction of polymer and silica has to be enhanced by using a polar co-monomer such as 4-vinylpyridin (4-VP) [19]. The increased interaction between polymer and silica resnlts in an improved encapsnlation of the silica [20]. 

V. Medout-Marere, A. El Ghzaoui, C. Chamay, J.M. Douillard, G. Chauveteau, S. Partyka, Surface Heterogeneity of Passively Oxidized Silicon Carbide particles Hydrophobic-Hydrophilic partition. J. Colloid Interface Sci. 223(2), 205-214 (2000). doi 10.1006/jcis. 1999.6625 J.M. Douillard, Concerning the thermodynamic consistency of the "Surface Tension Components" equations. J. Colloid Interface Sci. 188(2), 511-515 (1997). doi 10.1006/jcis. 1997. 4768... 

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