Polyelectrolytes weak polyacids

This potential reflects itself in the titration curves of weak polyacids such as poly(acrylic acid) and poly(methacrylic acid) [32]. Apparent dissociation constants of such polyacids change with the dissociation degree of the polyacid because the work to remove a proton from the acid site into the bulk water phase depends on the surface potential of the polyelectrolyte. 

At neutral pH, both a weak polyacid and a weak polybase are partially ionized, resulting in the formation of the polyelectrolyte complexes. 

Weak polyelectrolytes, on the other hand, become ionized within a specific pH range, creating a mechanism for the disassembly of the polymer multilayers. The most common examples of weak polyelectrolytes include polyacids, such as poly(acrylic acid) (PAA) and poly(methacrylic acid) (PMA). A decrease in the pH below the pKa of the polymer decreases the charge on the polymer, thus destabilizing the electrostatic interactions within the multilayers. The properties of films assembled from weak polyelectrolytes are highly dependent on the charge density, which can be tuned by both the salt concentration and pH [10]. 

A combination of the molecular polyelectrolyte theory with the methods of statistical mechanics can be used at least for the description of the chain expansion due to charges along the polysaccharide chain. The physical process of the proton dissociation of a (weak) polyacid is a good way to assess the conformational role of the poly electrolytic interactions, since it is possible of tuning poly electrolyte charge density on an otherwise constant chemical structure. An amylose chain, selectively oxidized on carbon 6 to produce a carboxylic (uronic) group, has proved to be a good example to test theoretical results. ... 

S. T. Dubas, J. B. Schlenoff, Polyelectrolyte multilayers containing a weak polyacid construction and deconstruction, Macromolecules 2001, 34, 3736. 

A weak polybase is fully charged at low pH and uncharged at high pH, whereas weak polyacids are fully charged at high pH and uncharged at low pH. The exact pH at which weak polyelectrolytes become fully charged of course depends on the chemical nature of the polymer. 

PAA is a typical weak polyacid and has been widely used as a model to investigate protein-polyelectrolyte interactions. BallaulTs group systematically studied BSA adsorption on so-called "spherical polyelectrolyte brushes" (SPBs) consisting of a polystyrene (PS) core covered with PAA brushes (as shown in Figure 7.4)... 

The existence of a discontinuity in the concentration dependence of the reduced viscosity has already been reported for many polyelectrolytes of different natures which indicates that the Fuoss relation is no longer valid at high dilution. Maxima have been reported for both weak and strong polyelectrolytes and many explanations have been proposed e.g. absorption of carbon dioxyde [7], hydrolysis of ionized groups [8], purity of the solvent [9], effect of rate of shear [10]. If the presence of carbon dioxyde can lead to a decrease of viscosity in the case of a weak polyacid, it can be reasonably excluded for the precise case of PVP (pH 4). Owing to the relatively low molecular weight of PVP (M 8 x 10 ), the effect of rate of shear can also... 

Ahmadiannamini, R, X. Li, W. Goyens, N. Joseph, B. Meesschaert, and I. F. J. Vankelecom. 2012. Multilayered polyelectrolyte complex based solvent resistant nanofiltration membranes prepared from weak polyacids. J. Memb. Sci. 394-395 98-106. 

Over the last years, there has been a growing interest in PECs based on natural and synthetic polymers. Chitosan is a natural polyaminosaccharide and a weak base. Its PECs with different natural and synthetic polyacids such as, carboxy-methylcellulose [29, 30], alginic acid [23], poly (acrylic acid) [31] are known. Besides alginate, carboxymethylcellulose, carrageenan, and dextran sulfate are the most extensively studied polysaccharides used in the formation of polyelectrolyte complexes [32, 33]. Some synthetic polyelectrolytes, like poly(l-lysine) and polyacrylates, have been used to make complexes with these polysaccharides [34]. In the above mentioned literature one can find different examples of PEC as well as various methods of forming them. 

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