Pickering stabilizer systems

Figure 9.6 Particle size distribution of PS depends on the conversion, using picker-ing stabilizer system (1) 24.3% (2) 44% (3) 51 % (4) 57% (5) 70% conversion...

It was discussed that the structure created by the ternary system oil/water/ nanoparticle follows the laws of spreading thermodynamics, as they hold for ternary immiscible emulsions (oil 1 /oil 2/water) [114,116,117]. The only difference is that the interfacial area and the curvature of the solid nanoparticle has to stay constant, i.e., an additional boundary condition is added. When the inorganic nanoparticles possess, beside charges, also a certain hydrophobic character, they become enriched at the oil-water interface, which is the physical base of the stabilizing power of special inorganic nanostructures, the so-called Picker-... 

It is appropriate at this point to indicate our personal motivation for carrying out structural studies, the types of compounds we study, and the experimental conditions we employ. In a very general sense we are interested in the bonding of small molecules and ions, e.g., 02, N2, NO, N2 R+, olefins, and acetylenes, to transition-metal complexes. Because of our interest in bonding, we seek the best solutions we can attain. Rapid, qualitative answers to conformational problems are not our interest. Since those transition-metal systems that bind small molecules generally have the metal in a low oxidation state, and since a low oxidation state is usually stabilized by ligands of the type PR3 (R = alkyl or aryl), solution to our problems involves typically the determination of a large number of structural parameters. With only a few exceptions the intensity data are obtained at room temperature on a Picker FACS-1 computer-controlled diffractometer. Usually the ratio of observations to variables is at least 10, and it is often 20 to 30. 

Fang et al [89] have also used Pickering emulsion polymerization (Figure 14.12a) fabricate clay-coated PANI particles by employing exfoliated clay sheets as a stabilizer. PANI particles with a fairly broad size distribution indicate a quite rough surface, which is composed of exfoliated clay sheets (Figure 14.12b). The PANI/clay nanocomposite particles have been employed as an ER material and exhibit similar ER behavior (Eigure 14.12c) to other typical ER systems. 

Nanoparticles in the GML/tetradecane/water system could also be formed in the presence of clay particles. The authors assumed a Pickering emulsion-like stabilization by the clay particles which are of disk-like shape with about Inm thickness and 30 nm diameter. Detailed information about the stabilization mechanism within these systems remains, however, still to be obtained. The use of clay particles as stabilizers holds some promise with regard to the preparation of "emulsifier-free" systems which are very interesting for pharmaceutical purposes. Hydrolysis of the monoglyceride was, however, pronounced in these dispersions due to the comparatively high pH introduced by the clay particle suspension. 

As mentioned in the introduction, the difference between a surfactant stabilized foam and Pickering foam is that the particles are much stronger attached to the air/water interface than surfactant molecules. Therefore the system is kinetically... 

---