Hydrophobisation

For elimination of intramolecular energy losses, we have synthesized ligands with high hydrophobisity - perfluoro-P-diketones R -CO-CH -CO-R, (R = CgF j or CgF R = phenyl or a-thienyl), that without second ligand eliminate completely water molecules from the inner coordination sphere. These ligands we have used in analysis at determination of Sm, Eu, Nd, Yb microamounts in high-purity lanthanide and yttrium oxides. 

In an earlier study in this laboratory (8) it had been shown that PS does not adsorb onto hydrophobised (methylated) silica from DMF. It is clear from the present results, however, (sample S12/PS 19, table III) that PS does adsorb onto silica particles which retain their surface hydroxyl groups, despite the strong hydrogen bonding between DMF and these groups referred to above. However, this adsorption is weak and reversible, since the PS... 

It may be seen from fig.A that post-hydrophobisation of the surfaces of the SiC -g-PS particles (compare S12/PS13b with S12/PS13b) makes little or no difference to their critical flocculation behaviour. This is not unexpected, since the grafted PS tails will, effectively, mask any contribution from the surface groups. 

The partition coefficient Kq of an organic compound in the 1-octanol/water system is used to assess the bioaccumulation potential and the distribution pattern of drugs and pollutants. The partition coefficient of imidazole and ILs strongly depends on the hydrogen bond formed by these molecules and is less than one due to the high solubility in water. The low value of the 1-octanol/water partition coefficient is required for new substances, solvents, insecticides to avoid bioaccumulation. Kqw is an extremely important quantity because it is the basis of correlations to calculate bioaccumulation, toxicity, and sorption to soils and sediments. Computing the activity of a chemical in human, fish, or animal lipid, which is where pollutants that are hydrophobic will appear, is a difficult task. Thus, it is simpler to measure the 1-octanol/water partition coefficient. This parameter is used as the primary parameter characterizing hydrophobisity. 

Figure 1. Dependence of surface pressure on total Langmuir trough area for silanized glass particles 75 15 pm in diameter with different hydrophobisation degree (thin lines) according to Horvolgyi et al. 27 theoretical calculations used Eq. (14) (bold solid line) and Eq. (15) (bold dashed line) with model parameters given in Table 1.

Interactions between hydrophilic monolayers have deserved considerable attention due to their importance in understanding phenomena that govern stability and fusion of biological membranes. For instance, Claesson et al. [95] have characterised the forces acting between dihexadecylphosphate (DHP) monolayers supported by dioctadecyldimethylammonium chloride hydro-phobised mica and compared the stability of DHP layers on hydrophobic mica surfaces. The authors demonstrated that less than 2% of all DHP molecules deposited onto hydrophobised mica surfaces are charged at pH 5-6. The... 

Fig. 7. Force normalised by radius as a function of surface separation between layers of DHP deposited onto hydrophobised mica surfaces measured in NaCl solutions of 2x 10 4M ( ), 1 x 10 3M ( ), 1 x 10 2M (o), at PH 5.2-5.1. At pH 9.5 no attraction was observed at any separation. The solid lines are force curves calculated from DLVO theory. The dashed line represents the part of the force curve that cannot be explained by the DLVO theory. This is a repulsive hydration force. Reprinted with permission from Ref. [95]. 1989, American Chemical Society.

In order to form an asymmetric film the gas bubble was pressed onto the surfactant solution/organic phase interface. Asymmetric film can also be obtained in this device when a drop of the organic phase is pressed onto the surfactant solution/air interface. This cell is very useful for the study of foam films in the presence of antifoams. The cells usually employed in the studies with antifoams cannot give reliable results because of the strong hydrophobisation of the capillary. 

The attainable enrichment and clean-up in SPE depend primarily on the selectivity and affinity of the sorbent for the selected target analyte or analytes, the sample load capacity for the analytes and the rate of mass transfer to and from the binding sites, the latter affecting the minimum desorption volume and thus the enrichment that can be obtained. Other factors of importance are the reproducibility of the recovery yields and the stability and reusability of the sorbent when online procedures are desired. For hydrophobic analytes satisfactory results are usually obtained using standard reversed phase sorbents. Thus hydrophobised silica (C8, Cl8), styrene-divinylbenzene copolymers (PS-DVB) and graphitised carbon black (GCB) are the conventional sorbent materials used in SPE (Fig. 15.2)... 

Fig. 6.13. Hydrophobising an oxide surface by treatment with a silane coupling agent (redrawn...

Advancing contact angle of boehmite sol with a PVA on a hydrophobised alumina substrate. The sol also contains non-ionic surfactant. Angle measurements were made on small droplets on the substrate with a goniometer. 

Another function of surface active polymers such as PVA is their wetting action. This can be seen from Table 6.5 where the advancing contact angle of small droplets of boehmite sol with non-ionic surfactant on a hydrophobised alumina substrate are given for increasing PVA concentration. Aging time of the droplets on the substrate was 4 min. 

With particles containing rough edges, the situation is more complex, as demonstrated by Johansson and Pugh [32], using finely ground quartz particles of different size fractions, the surfaces of which had been hydrophobised by methylation. The results of these studies and others confirmed the importance of the size, shape and hydrophobicity of the particles on foam stability. 

The synergetic antifoaming effect of mixtures of insoluble hydrophobic particles and hydrophobic oils, when dispersed in an aqueous medium, has been weU established in the patent Hterature. These mixed antifoamers are very effective at very low concentrations (10-100 ppm). The hydrophobic particles may be hydrophobised silica and the oil is PDMS. 

Figure 17.3 Force-distance curves between hydrophobised glass surfaces containing adsorbed INUTEC SPl in water.

Anfruns Kitchener (1976) examined the efficiency of capture of several fractions of hydrophobised (methylated) quartz by individual bubbles of 0.5-1.1 mm in diameter. 

Towards total hydrophobisation of MCM-41 type silica surface... 

Towards total hydrophobisation of MCM-41 type silica surface T. Martin, A. Galarneau, D. Brunei, V. Izard, V. Hulea, A.C. Blanc, S. Abramson,... 

Adsorption (as well as chemisorption) processes can lead to a drastic change of the surface nature, i.e. its hydrophilisation or hydrophobisation (oleophilisation). A criterion of the surface nature is the wetting contact angle 0. When a drop of a liquid is applied on a solid surface, then three different interfaces are formed (Fig. 6.1) with the corresponding tensions Ysg Tig and ysi. 

Selectivity of the flotation process is determined by both selective hydrophobisation of mineral particles and conditions of their aggregation, stability and conditions of destruction of three-phase flotation foams. 

Most common is the theory of chemisorption of collectors at the surface of solid particles. However, it is, as a rule, at the same time noted that simultaneously concurrent processes take place, which are connected both with adsorption of surfactants at 1/g interfaces and with their interaction with ions in the flotation pulp. Thus, it is shown in [66] that saturated C 2—Cj4 fatty acids are selectively chemisorbed on calcium carbonate surfaces which provides them with an effective hydrophobisation. At the same time, C5—Cg acids are adsorbed mainly at 1/g interfaces which produces a substantial influence on the stability of the flotation foams. Free and Miller [67] have thoroughly investigated the behaviour of sodium oleate in the flotation of a calcium mineral, fluorite. It has been established that calcium dioleates are formed both in the bulk and at 1/s interfaces. In this case, an effective hydrophobisation of the surface of fluorite particles takes place both due to the interaction of oleate with calcium ions on the active sites and by adsorption of calcium dioleates formed in the solution. It has been once more confirmed [68] that classical collecting agents, xanthogenates, e.g. ethyl xanthogenate, form on the... 

In case of using mixtures of two and more collectors, the selective hydrophobisation is accomplished simultaneously both due to chemisorption and physical adsorption. It is shown in [69] that the simultaneous use of fatty acids and hydrocarbon oils for calcium phosphate flotation from quartz different processes are observed. Fatty acid soaps form chemical compounds on the surface of the material floated, after which the hydrocarbon oil physically adsorbs. It has been experimentally established that hydrocarbon oil is transferred from quartz particles to the surface of floated phosphate. When using mixtures of anionics and nonionics, hydrophobisation of particle surfaces is also accomplished both due to the formation of chemical compounds and physical adsorption which is confirmed by measurements of the zeta-potential of the particles floated [70]. 

Flotation has been used for more than 100 years to separate sulphides, oxides and other salts from ores, as well as to obtain phosphates, barite, chromite and other materials. Up to 90% of copper, lead, nickel, zinc are extracted using flotation in the USA [152 - 153]. In Russia, flotation is widely used to additionally obtain apatite, barite and phosphates. Flotation of iron oxides is not used in practise yet, but the number of experiments carried out in this direction is rather large. The main physicochemical principles of flotation have been discussed above [59 -74]. Here, only some practical problems will be discussed. In [153], requirements are pointed out which apply to three-phase flotation foams, and the main components of the process are defined, i.e. surfactant - collector surfactant - frother activator, depressants, colligend, gangue. The peculiarities of flotation and foam separation in batch and continuous modes are outlined as well as the structure and properties of the main types of flotation agents described. As surfaces of the majority of mineral particles are hydrophilic in nature, hydrophobisation of particles is necessary for a selective separation. 

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