Polyelectrolytes titration

Colloid (or polyelectrolyte) titration . Charge may also be measured volumetrically using the principle of colloid titration which relies upon the fact that polymers of opposite charge can be stoichiometric-ally charge titrated in aqueous solution. A cationic polyelectrolyte (C) can be titrated with an anionic polyelectrolyte in the presence of an appropriate indicator (I) as follows ... 

The signal determined in arbitrary units is a complex dimension, which cannot be directly quantified to the zeta potential. Its sign is determined by the charge of the cell wall. It summarizes contributions from the cell wall, the piston, and the whole colloidal material. Thus for a quantitative calculation of the particles surface charge density a polyelectrolyte titration has to be carried out. If one knows the specific surface, for zeta potentials <30 mV it can be calculated according to... 

Wassmer KH, Schroeder U, Horn D. Characterization and detection of polyanions by direct polyelectrolyte titration. Makromol Chem 1991 192 553-565. 

FIGURE 56.5 Potentiometric, conductometric, and turbidimetric titration curve of a polyelectrolyte titration. (With kind permission from Springer Science-I-Business Media Polyelectrolytes in Polyelectrolytes and Nanoparticles, 2007, pp. 5-45, Koetz, J., Kosmella, S., Howard, G., Barth, D., and Harald, P., Springer, Berlin, Germany.)... 

In contrast to the formation of PEC structures in situ, PECs can also be formed before addition to the fibre suspension. We refer to these as pre-formed PECs. They are prepared by mixing two oppositely charged polyelectrolytes together in some way before further use as a paper chemical. The PEC preparation method that is predominantly used in the literature is polyelectrolyte titration, i.e., the slow addition of a solution of one polyelectrolyte to a solution of an oppositely charged one [11]. However, another PEC preparation method has recently been used, the so-called jet mixing method [50, 51]. 

The concentration of the surfactant were determined by titration with cetylbenzyldimethylammonium chloride, which forms water-insoluble complexes with the anionic surfactant. Potentiometric titrations were carried out with a Titroprocessor 672 (Metrohm, Switzerland) using a surfactant-sensitive electrode [7]. The cationic polymer was analyzed by polyelectrolyte titration with poly-(ethylensulfonate) (PES). The equivalence point of the polyelectrolyte complexation reaction was indicated either by streaming potential (PCD 2, Mutek GmbH, FRG) [8] or, for lower concentrations of the cationic polymer, by a color change due to the cooperative binding of a metachromic dye on the excess chromotrope titrant [9, 10]. Brilliant Yellow was used as dye indicator. 

In order to characterize the effective surface charge, the amount of sulphate and carboxylic groups on the colloids was determined by polyelectrolyte titration [39]. At pH 7 the Z-potential of the polystyrene colloids was about —55 5 mV in water. 

For unmodified silica dispersions, the surface charge is the main stabilizing factor. Surface charge of colloidal siUca dispersions can be measured by cationic polyelectrolyte titration [54], The surface charge of two unmodified silica dispersions and the corresponding silane-modified siHca dispersions were made by titration of the said dispersions with a Polybrene solution, 4 g per liter. All silica dispersion had a concentration of 5 g SiO per liter. To compensate for the presence of soluble silicate species in the silica dispersions, the latter were quantitatively determined by using the ammonium heptamolybdate method [55]. 

The reaction of a positively charged polyelectrolyte with a negatively charged polyelectrolyte produces a precipitate, forming the basis for a precipitation titration. This paper provides an overview of colloid titrations, discussing... 

Usually the acid-base properties of poly electrolyte are studied by potentiometric titrations. However it is well known, that understanding of polyelectrolyte properties in solution is based on the knowledge of the thermodynamic properties. Up to now, there is only a small number of microcalorimetry titrations of polyelectrolyte solutions published. Therefore we carried out potentiometric and microcalorimetric titrations of hydrochloric form of the linear and branched polyamines at 25°C and 65°C, to study the influence of the stmcture on the acid-base properties. 

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. 

Extensive data are given in the Uterature for the potentiometric titration of polymer acids which may be used to study the behaviour of polyelectrolyte systems under different conditions. For poly(a-D) galacturonic acid there are few data of this kind, especially in connection with the occurrence of a conformational transition induced by pH variations, or with the effect brought about by the addition or the exchange of counterions. Since for a polyacid not exhibiting a conformational transition in the course of titration, pK K denoting the apparent dissociation constant) increases monotonously with degree... 

J Hasa, M Ilavsky, K Dusek. Deformational, swelling, and potentiometric titration of polyelectrolytes. J Polym Sci Polym Phys Ed 13 253-262, 1975. 

KPVS) and the indicator is usually o-toluidine blue (OTB). It is necessary for kx to be much larger than k2 (which is usually the case for poly electrolytes). If for example a cationic poly electrolyte together with OTB is titrated with KPVS, a polyelectrolyte complex is initially formed until no free polyelectrolyte is left to react with the KPVS. At this point, KPVS starts to react with OTB and a colour shift from light-blue to purplish-red indicates the end point. The titration relies upon the formation of a 1 1 complex, which is generally true provided that the ionic strength is low. 

The method can be applied to charges of solids such as fibres and fillers by equilibrating a known excess of cationic polyelectrolyte (for anionic paper furnishes) with the furnish. The solid phase is then separated and the residual polyelectrolyte in the filtrate is back-titrated ... 

The relatively high charge density along the backbone chain of a polyelectrolyte leads to some interesting properties. Titration data show that counterions (including protons in polyacids) bind to polyelectrolytes more readily than they bind to monomeric electrolytes. This effect arises from the additivity of electrostatic interactions between polymer-fixed ions and counterions. At high... 

Polyelectrolyte complexation in aqueous solution between PEI and PMAA has been studied through viscometry, conductometry, potentiometry, and IR spectroscopy [90]. Upon addition of increasing concentrations of PMAA to an aqueous PEI solution, viscosity dropped suddenly around a 1 to 4 ratio of PMAA to PEI because of the complexation and subsequent coiling of the complexed chains. Reduced viscosity then rose past this ratio indicating that the stoichiometry of the complex occurs in a 1 4 (PMAA groups PEI groups) formation. Conductance and titration experiments agreed with this theory. The... 

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