Stabilisers, colloid

Underwood S M, Taylor J R and van Megen W 1994 Sterically stabilised colloidal particles as model hard spheres Langmuir O 3550-4... 

Near-hard Sphere Fluids - a Step Towards Stabilised Colloids... 

During the 1930 s a clearer idea of the role of the electrical double layer in stabilising colloidal particles began to emerge, particularly in the work of Verwey (5), Kruyt (6) and Derjaguin (7). In 1938 in a classic paper Langmuir (8) showed that when an overlap of double layers occurred, with two flat plates whose surfaces were at the same electrostatic potential, then a repulsion pressure was developed between them. 

Silicic acid,1 in a form which is soluble and chemically pure, can be obtained by employing a divided cell with alkali silicate in the anode compartment. Perforated electrodes are fitted against the diaphragm wall, and during electrolysis alkali diffuses into the cathode compartment whilst silicic acid remains in the anode compartment. Hydrated silica is thus separated in a pure form specially suitable for stabilising colloids. 

Polyelectrolyte brushes are macromolecular monolayers where the chains are attached by one end on the surface and, at the same time, the chains carry a considerable amount of charged groups. Such poly electrolyte structures have received thorough theoretical treatment, and experimental interest has been vast due to the potential of brushes for stabilising colloidal particle dispersions or for... 

Stabilised colloids are not retained by MF if the primary colloids are smaller than the membrane pores... 

Figure 5.4 Flux ratio (flux after collection of 800 mL permeate over pure water flux) as a function of primary colloid sit e for stable colloids (pH3), aggregates in the absence of organics (pH8), stabilised colloids (OPS), and aggregates (SPO).

Figure 5.9 Flux ratio as a function of calcium concentration (A) for stabilised colloids (OPS) and (B) for aggregates (SPO, Gl WP membrane).

Experiments were carried out at 0.5, 2.5, and 4 mM CaCH. Results are shown in Figure 5.9B, and the trend observed is to that of the SPO data. Calcium can destabilise colloids that were stabilised by-organics. This was observed to occur at a concentration between 2.5 and 4 mM CaCl 2, with a resultant increase in colloid rejection from 15 to 95% and a greater flux decline, as shown in Table 5.7 (No 1, 4, 5). Tills corresponds to the effect of calcium on stabilised colloids reported by Amirbahman and Olson (1995), which was described in more detail in Chapter 2. Deposition increased with calcium concentration, which indicates that the destabilisation is always present to some extent. The calcium was added after the colloids were stabilised with HA, which is a different scenario to NOM, where salt (which is in the NOM powder) is added simultaneously. In this case, the calcium provides a full destabilisation of the organic-coated colloids at 4 mM, leading to complete rejection and deposition. 

The filtration and rejection of stabilised colloids (OPS) was shown in section 5.8. The stable coUoids have a high negative surface charge and are not retained by the MF membranes, Adsorption on the membrane material is minimal - much less than in the absence of organics and at pH 3. 

Overall, the result with the greatest impact on water treatment is the low rejection of the stabilised colloids. Due to their low settlability, these systems will be most abundant in most streams and chemically pretreated feedwaters. 

The use of polymer-stabilised colloidal platinum clusters (containing cinchoni-dine) in acetic acid provides up to 97.6% ee in the reduction of methyl pyruvate (MeCOCOzMe). Polyvinylpyrrohdine is used as the polymer, and the particle size is small. The use of nanoparticles as a support for catalysts is an attractive concept owing to the large surface areas of these materials. However, such supported catalysts of this type are often difficult to recover. Hu and coworkers have achieved the immobilisation of ruthenium(phosphine)( 1,2-diamine) catalysts onto... 

Polyphosphates have the ability to stabilise colloidal suspensions of other inorganic materials in aqueous media—an effect which is probably due to complex formation on the surface of the particles. 

Eastman J (2010) Stability of charge-stabilised colloids, hr Colloid scitaice principles, methods and applications, 2nd cdn. Wiley-Blackwell... 

Prepare a solution of stabilising colloid in water in the reaction vessel and add ammonium persulphate. 

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