Polyelectrolyte colloidal suspensions

Leong, Y.K., Scales, P.J., Healy, T.W., Boger, D.V. (1995). Interparticle forces arising from adsorbed polyelectrolytes in colloidal suspensions. Colloids and Surfaces A Physicochemical and Engineering Aspects, 95, 43-52. 

Waste water, containing a variety of colloids, is often treated by polymeric flocculants such as polyacrylamides to precipitate the colloidal material and make it better filterable. Quite often these flocculants are high-molecular-weight weakly charged polyelectrolytes. Bacterial suspensions resulting from biological waste water treatment must also be flocculated before they can be properly separated from the purified effluent by sedimentation or filtration. 

Electrostatic interactions are present in materials that contain ions. These include aqueous solutions of acids, bases, salts, polyelectrolytes (i.e., charged polymers), as well as colloidal suspensions of charged particles or droplets. Although fluids containing charged surfaces and mobile ions maintain electroneutrality overall, locally there are often eharge imbalances. 

In colloidal suspensions of polyelectrolytes, where the existence of two phases is not discernible by visual observation, the concentration of Na+ ions, CNa, is given by Equation 21 instead of by Equation 14. 

Polyelectrolytes, except those which are covalently cross-linked, are soluble in water, and their applications are based on this property. Basically, these applications depend on the polyelectrolyte altering the fluid properties of an aqueous medium, or modifying the behavior of particles in aqueous slurries or colloidal suspensions. 

It was recognized very early (5), however, that the corresponding effect in a colloidal suspension (the CVP) should be much larger and easier to use since in that case the dipole would be created by the particle and its surrounding double layer. That has proved to be the case and the application of the method to the investigation of polyelectrolytes and proteins has been reviewed by Zana and Yeager (3). More recently, the application of the CVP method to colloidal suspensions and emulsions has been reviewed by Marlow et al. (6) and the more recent developments will be discussed in the next chapter. Here, we will concentrate on the developments in the alternate electroacoustic procediue, the ESA effect. This refers to the production of a sound wave when a high-frequency electric field is applied to a suspension or emulsion. 

Videomicroscopy of colloid suspensions finds that colloid particles in nondilute solutions form fast- and slow-moving clusters studies of Sedlak on the polymer slow mode indicate that random-coil polyelectrolytes also form slow and fast regions(12). Colloidal probes in colloid or polymer solutions both sometimes show re-entrance, in which the concentration dependences of D and rj differ, but only over a limited range of c. At large q and elevated c, the polymer slow mode sometimes becomes -independent, especially at low temperatures. A similar large- behavior does not appear to have been reported for spheres. 

We demonstrated how ordered lines of colloidal polystyrene particles can be achieved by a simple dip coating process [70], We used wrinkles produced via a stretch retraction process of a glassy polyelectrolyte multilayer film mounted on a PDMS substrate. Here, the template was dipped into a colloidal particle suspension with the orientation of the wrinkle s grooves with the withdrawing direction of dipping as the sketch in Fig. 11 indicates. 

The most important factor influencing the degree of steric stabilization is the thickness of the adsorbed layer in comparison with the size of the particles [292], The term protection has also been used because the steric stabilizing effect can cause significant salt tolerance on the part of a colloidal dispersion. Some suspensions have been prepared, using high concentrations of polyelectrolytes, that are quite stable in concentrated salt solutions [49]. 

Stable suspensions are necessary to obtain homogeneous casts by colloidal filtration. Different kinds of stabilisation mechanisms for alumina suspensions are used in literature. Pure electrostatic stabilisation can be obtained using HNO3, while electrosteric stabilisation is obtained using polyelectrolytes like PolyMethylAcrylicAcid (PMAA) and PolyAcrylicAcid (PAA). In... 

FIG. 13 The amount of NaCl needed to flocculate a clay (i.e., sodium bentonite suspension) as a function of the polyelectrolyte concentration (i.e., sodium car-boxymethylcellulose). The inserted figure is an enlargement of the initial addition of the polyelectrolyte. The lines are redrawn from An Introduction to Clay Colloid Chemistry by van Olphen [51]. 

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