Polyelectrolyte microgel

Fig. 1.6 Schematic representation of a lignosulfonate polyelectrolyte microgel unit.

In a related application, polyelectrolyte microgels based on crosslinked cationic poly(allyl amine) and anionic polyfmethacrylic acid-co-epoxypropyl methacrylate) were studied by potentiometry, conductometry and turbidimetry [349]. In their neutralized (salt) form, the microgels fully complexed with linear polyelectrolytes (poly(acrylic acid), poly(acrylic acid-co-acrylamide), and polystyrene sulfonate)) as if the gels were themselves linear. However, if an acid/base reaction occurs between the linear polymers and the gels, it appears that only the surfaces of the gels form complexes. Previous work has addressed the fundamental characteristics of these complexes [350, 351] and has shown preferential complexation of cationic polyelectrolytes with crosslinked car-boxymethyl cellulose versus linear CMC [350], The departure from the 1 1 stoichiometry with the non-neutralized microgels may be due to the collapsed nature of these networks which prevents penetration of water soluble polyelectrolyte. 

The polyelectrolyte microgels have been established as model soft spheres as, in addition to the above features, their softness and properties can be tuned by altering the physico-chemical environment (pH, ionic strength, degree of ionization) [152-160], The response varies from that of colloidal (polydisperse hard-sphere) suspensions and that of polymer gels and in this respect such microgels fit within the theme of Fig. 1 [157-160],... 

Fig- 2 Generic structure of concentrated dispersions above close-packing (a) polyelectrolyte microgels [47] (particle diameter d 0.2 lm) (b) oil in water emulsion [102] (dss2 lm) (c) multilamellar vesicles [103] (d 5 pm). (Pictures are reproduced with permission of the authors)... 

Antonietti M. Structure and viscosity of spherical polyelectrolyte microgels a model for the polyelectrolyte effect Polymer and Colloid NATO ASI, Les Houches, Sept 14-24, 1999. 

FIG. 7 Typical dependence of the swelling ratio a of a polyelectrolyte microgel on the number v of subchains in a sample. 

Effect of Electrolyte, Emulsions stabilized with hydrophobically modified poly(acrylic acid) are sensitive to electrolytes. Upon contact with a brine solution, emulsion stability is immediately lost, and rapid coalescence of the oil droplets ensues (Figure 23). This instability can be understood by consideration of the Donnan equilibrium of counterions in polyelectrolytes (discussed earlier in this chapter). Addition of salt causes collapses of the polyelectrolyte microgels that are adsorbed at the oil-water interface. Shrinkage of the microgels could conceivably lead to immediate loss of stability, as depicted schematically in Figure 24. 

Cloitre, M., Borrega, R., Monti, R, and Leibler, L. 2003. Structure and flow of polyelectrolyte microgels From suspensions to glasses. C. R. Physique 4 221-230. 

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