Solid hydrophobic

If a hydrophobic solid is suspended in water and a small amount of oil is added to the system, the oil will preferentially wet out the solid. If a sufficient amount of oil is added, the oil films are brought together and coalescence (a first-order reaction) and agglomeration (a second-order reaction) take place. 

For example, a synergistic defoaming occurs when hydrophobic solid particles are used in conjunction with a liquid that is insoluble in the foamy solution [652]. Mechanisms for film rupture by either the solid or the liquid alone have been elucidated, along with explanations for the poor effectiveness, which are observed with many foam systems for these single-component defoamers. 

The above statements are adequate for liquid defoamers that are insoluble in the bulk. Experience has proven, however, that certain dispersed hydrophobic solids can greatly enhance the effectiveness of defoaming. A strong correlation between the effectiveness of a defoamer and the contact angle for silicone-treated silica in hydrocarbons has been established [300]. It is believed that the dewetting process of the hydrophobic silica causes the collapse of a foam by the direct mechanical shock occurring by this process. 

G. C. Frye and J. C. Berg. Mechanisms for the synergistic antifoam action by hydrophobic solid particles in insoluble liquids. J Colloid Interface Sci, 130(1) 54—59, June 1989. 

Cytotoxins obtained from cobra venom (Naja naja atra). Hydrophobic solids that cause irreversible depolarization of cell membrane and cellular destruction as well as contraction of skeletal and smooth muscle, including the heart. 

Obviously, the spreading of water on a hydrophobic solid is helped by adding a surfactant. yLV and ySL are reduced, thus, on both accounts cos 0 (Eq. A.4.3) increases and 0 decreases. 

Chander, S. and Fuerstenau, D. W., 1975. Sulphide minerals with thiol collectors the chalcocite diethy dilhiophosphate system. 11th International Mineral Processing Congress, 1 583 - 603 Chander, S., Wie, J. M., Fuerstenau, D. W., 1975. On the native floatability and surface properties of naturally hydrophobic solids, hr P. Somasunfaran and R. G. Grieves(eds.), Advances in Interfacial Phenomena of Particulate/Solution/Gas Systems. AIME Symp., Ser., 150(71) 183-188... 

As opposed to vapor, it is necessary to differentiate between hydrophilic and hydrophobic solids. This also applies to bacteria and viruses since they are transported primarily in solutions. ... 

Chengara A, Nikolov A, Wasan D (2002) Surface tension gradient driven spreading of trisiloxane solution on hydrophobic solid. Colloid Surf A 206 31-39... 

Most general-purpose release agents have been developed for this market in part because of their low toxicity and chemical inertness and do not usually present health and safety problems. Some of the solvent dispersions require appropriate care in handling volatile solvents, and many suppliers are offering water-based alternatives. Some of the solids, particularly finely divided hydrophobic solids, can also present inhalation problems. Some of the metallic soaps are toxic, although there is a trend away from the heavier, more toxic metals such as lead. The reactive type of release coating with monomers, prepolymers, and catalysts often presents specific handling difficulties. The potential user with health and safety questions is advised to consult the manufacturer directly. 

C. The Interaction of Hydrophobic Solids with Organic Liquids. 283... 

Figure Ic differs markedly from those obtained for the immersion of polar solids in water initially the heat values are small but increase with increasing amounts of preadsorbed water. Thus far, only one such curve has been reported in the literature for the system Graphon-water 90). Graphon is a graphitized carbon black which has an essentially homogeneous, homopolar surface 21). Nevertheless, a small fraction of heterogeneous sites is responsible for the limited adsorption of water on the surface of this solid. Similar curves can be expected for other hydrophobic solids.

Let us now come back to the issue of linearity of the isotherm and dependency of Kld on the sorbate concentration. In numerous field studies in which both particle-associated and dissolved concentrations of PAHs are measured, apparent Kioc values are up to two orders of magnitude higher than one would have predicted from a simple absorption model (Gustafsson and Gschwend, 1999). If a natural soil or sediment matrix includes impenetrable hydrophobic solids on which the chemical of interest may absorb, the overall Kioc value must reflect both absorption into recent natural organic matter and absorption onto these surfaces. 

The wetting of a hydrophobic solid surface by an aqueous medium is considerably helped by the addition of surface-active agents. Wa is increased and yLG is decreased (Figure 6.4b), so that, from the Young-Dupre equation, 0 is reduced on two counts. 

Arbiter, N. Fujii, Y. Raja, A. Surface Properties of Hydrophobic Solids in Advances in Interfacial Phenomena of Particulate/Solution/ Gas Syatems Applications to Flotation Research, Somasundaran, P. Grieves, R.B. (Eds.), American Institute of Chemical Engineers New York, 1975, pp. 176-182. 

The two liquids thus formed are immiscible, but in thermodynamic equilibrium. Therefore, we may speak of a dynamic system of two immiscible phases. Figure 3.10 shows an example of a practical system applied to create a dynamic LLC phase system. A practical phase system can be created by pumping a mobile phase through a column, the composition of which corrresponds to a ternary mixture that is in dynamic equilibrium with another mixture (the two mixtures can be connected by a nodal line). If the mobile phase is the more polar one of the two ternary mixtures in equilibrium, then a non-polar (hydrophobic) solid support must be used and a reversed phase system can be generated. If the mobile phase is the less polar of the two mixtures in equilibrium, a polar support is required. 

Surfactants adsorb on solid surfaces due to hydrophobic bonding, electrostatic interaction, acid-base interaction, polarisation of rr electrons and dispersion forces. Hydrophobic bonding occurs between the hydrophobic surfactant tail and the hydrophobic solid surface (tail down adsorption with monolayer structure) or between the hydrophobic tails of the surfactant adsorbed on the hydrophilic solid surface and the hydrophobic tails of the surfactant from the liquid phase (head down adsorption with bilayer structure) [54, 55]. 

Electrostatic interactions occur between the ionic head groups of the surfactant and the oppositely charged solid surface (head down adsorption with monolayer structure) [56]. Acid-base interactions occur due to hydrogen bonding or Lewis acid-Lewis base reactions between solid surface and surfactant molecules (head down with monolayer structure) [57]. Polarisation of jt electrons occurs between the surfactant head group which has electron-rich aromatic nuclei and the positively charged solid surface (head down with monolayer structure) [58]. Dispersion forces occur due to London-van der Waals forces between the surfactant molecules and the solid surface (hydrophobic tail lies flat on the hydrophobic solid surface while hydrophilic head orients towards polar liquid) [59]. 

FIGURE 4.27 Wetting a hydrophobic solid surface with the aid of a wetting agent. 

Water-soluble polymers coat hydrophobic solid surfaces with multilayers and thus render the solid hydrophilic (i.e., wetting). The number of adsorbed chains (or the amount of polymer adsorbed) per surface site (or unit weight of adsorbent) is related to the volume fraction of segments in each layer. As the length of the chains increases,... 

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