Stabilisation dispersions

Dispersant stabilising group Dispersant adsorbing group... 

Dispersion stabilisation generally requires fairly complete coverage of particle... 

Recent studies in our laboratory (3) using polystyrene latex dispersions stabilised by the above "comb" dispersing agent have shown that polymers such as poly(ethylene oxide) induce wealc flocculation above a certain critical concentration of free polymer which was dependent on the molecular weight of the chain. 

A number of different metals have been used in powder form as additives to bonded molybdenum disulphide films. They include gold, silver, nickel and tantalum, and it has been suggested that they improve film life by helping to facilitate readhesion of lubricant debris to the substrate. Many other components have been added to bonded films as corrosion inhibitors, anti-oxidants, dispersion stabilisers and biocides, and many different solvents have been used. There is therefore an almost infinite variety of possible formulations, and several hundred have been produced commercially. 

It has been seen in Chapter 7 that the use of macromolecules as dispersion stabilisers depends in part on the osmotic forces arising from the interaction of solvated polymer chains as neighbouring particles approach (see Fig. 7.7). It is thus important to know how factors such as temperature and additive affect this interaction. Flory has given the free energy of dilution (the opposite process to the concentration effect discussed in section 7.2)... 

Surfactants have a role of dispersion stabilising almost any suspension. Moreover, they can adsorb themselves on solids [14], thus destabilising the suspension. So, with the surfactants concentration decreasing in solution, the colloids can flocculate or adsorb themselves on suspended solids, explaining both the decrease of colloids and surfactants in the sample. 

The third component, the graft species, acts as a nonaqueous dispersant (NAD), a compound having, in the same structure, polyetheric chains and vinylic polymer chains. This compound assures the stability of the resulting polymer dispersion and prevents sedimentation and coalescence of the vinylic polymer particles [1-5]. The mechanism of this dispersion stabilisation will be discussed later. The median diameter of solid particles for a performance polymer polyol is generally less than 1 [am, usually 0.2-0.5 im [30]. 

The graft polyether polyols, based exclusively on ACN or with a high ACN content (more than 50% ACN in the monomer mixture), do not need a special NAD due to the formation of graft species, the inevitable dispersion stabilisers formed in situ, the resulting dispersions being perfectly stable. 

A direct method to obtain an efficient macromer useful as NAD for polymer dispersion stabilisation is the PO homopolymerisation or random PO-EO copolymerisation initiated by fumaric acid and catalysed by DMC catalyst [53] ... 

Wetting, dispersing, stabilising Numerous anionic, non-ionic, cationic and amphoteric surfactants/dispersants... 

Copolymerisation of these macromonomers with norbomene or norbomene acetate has yielded a series of poly(norbomene)-graft-poly-(e-caprolactone) copolymers of well-defined structures. Furthermore, PCL macromonomers were also homopolymerised in high yield into high molecular weight comb chains of narrow molecular weight distribution MJM =1.10). Such copolymers have potential applications as surface modifiers, polymeric surfactants, compatibilisers in polymer blends, and dispersion stabilisers. 

This series of articles focuses on the polymerisation processes used to prepare polymers and resins utilised in the coatings industry. This article concerns latexes and emulsion polymerisation. Surfactants and dispersion stabilisation mechanisms, emulsion polymerisation ingredients and processes, particle nucleation, particle... 

Ceramic foams are produced from organic precursor foams such as polyurethane or polyolefins. Their pores are then filled with an aqueous slurry of the ceramic typically containing 20 wt.% of ceramic particles in the size range of from 0.1 to 10 pm [461]. Wetting agents, dispersion stabilisers and viscosity modifiers are added to the slurry. Suitable ceramics are alumina, alumina silicates, zirconia, stabilised zirconia and titania, amongst others. The pores ofthe precursor foam may be filled completely or only coated on their surface by the ceramic particles. The foam is then dried and calcined at 1000 °C, which removes the polymer and sinters the ceramic. Metallic foams have similar properties compared with ceramic foams, but superior mechanical stability and improved heat conductivity. 

Organic additives for dispersion stabilisation - a rich nutrient basis... 

Dispersion stabilisers help to maintain desirable physical properties of emulsions and other disperse systems. Various polysaccharides, such as gum arabic (E414), are used as dispersion stabilisers. 

For surface sizing mostly polymeric sizing agents are used. The most important product classes are acryhc copolymer dispersions stabilised by protective colloids. The particles of the sizing agent consist of a hydrophobic polymer core and a hydrophilic shell formed out of the protective colloid. 

---