Polymers bridging mechanism

A polymer molecule may also simultaneously adsorb onto both surface, hence causing flocculation by polymer-bridging mechanism [8], Figure 3.2 shown this behavior. 

Figure 7.13. Sequence showing schematically (a) charge-stabilized particles, (b) particles flocculated by the polymer bridging mechanism, and (c) particles restabilized by steric repulsive (chain overlap) interactions at higher levels of polymer surface...

A fourth mechanism is called sweep flocculation. It is used primarily in very low soflds systems such as raw water clarification. Addition of an inorganic salt produces a metal hydroxide precipitate which entrains fine particles of other suspended soflds as it settles. A variation of this mechanism is sometimes employed for suspensions that do not respond to polymeric flocculants. A soHd material such as clay is deUberately added to the suspension and then flocculated with a high molecular weight polymer. The original suspended matter is entrained in the clay floes formed by the bridging mechanism and is removed with the clay. 

This type of mechanism is likely to be partly operative in systems containing inorganic electrolytes as, for example, in the case of aluminium species. Some polyelectrolytes may also induce flocculation by charge neutralisation but the adsorbed polymer may also be able to bridge from one particle surface to another ( polymer bridging ). 

Flocculation of microorganisms is thought to be affected by a bridging mechanism of polymers excreeted by the microorganisms or exposed to the microbial surface under suitable physiological conditions. More recently new work on adhesion of bacteria have been carried out (Van Loosdrecht et al., 1990) see Chapter 7.9. 

In Section 2222, we described a bridging mechanism in which polymer was laterally squeezed away from the near-contact region upon approach of the droplets. 

Alternatively, several workers have shown that not only is the soluble, zero-charged hydrolysis product considerably more surface active than the free (aquo) ion but also a polymeric charged or uncharged hydrolysis product may be formed at the solid-liquid interface at conditions well below saturation or precipitation in solution. Hall (5) has considered the coagulation of kaolinite by aluminum (III) and concluded that surface precipitates related to hydrated aluminum hydroxide control the adsorption-coagulation behavior. Similarly Healy and Jellett (6) have postulated that the polymeric, soluble, uncharged Zn(OH)2 polymer can be nucleated catalytically at ZnO-H20 interfaces and will flocculate the colloidal ZnO via a bridging mechanism. 

The A values of polymer metal complexes with different polymer bridges (16a d), having redox couples Mt/M2, where Mt/M2 is Fe2+/3+ or Cu+/2+, at both terminals of the bridge, were estimated based on quantum mechanical treatment (Fig. 6), It was concluded that not only system (16a) but also system 16c may be adiabatic over... 

Fig. 3.2 Schematic representation for the mechanism of polymer-bridging flocculation. (From ref. [8])...

Although the linearity of the relationship between the effective stress and the number of polymer bridges confirms the general features of the bridging mechanism,... 

The original bridging mechanism was proposed by Ruehrwein and Ward in 1952 and later advanced by La Mer and co-workers. - Bridging is considered to be a consequence of the adsorption of the segments of individual polymer molecules on the surfaces of more than one... 

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