Apparent molal volumes of polyelectrolytes in aqueous solutions

Abstract

Using a precision densimeter, the densities of a series of carefully prepared and purified aqueous solutions of polyelectrolytes of accurately known concentrations have been determined. The following polyelectrolytes have been investigated: poly(methacrylic acid) (PMA) samples of various molecular weights, carboxymethylceliuloses of various substitution degrees (acid form and tetramethylammonium (TMA) salt), poly (acrylic acid) (PA A), poly(maleic acid-methyl vinyl ether), polyphosphate, poly (ethylenesulf onic acid), and poly-(styrenesulfonic acid). Measurements of densities have also been performed on the alkali metal and TMA salts of the last five polyelectrolytes. The densities have been, used for the calculation of the apparent molal volumes .In the concentration range investigated the plots 0 = f(concentration) have been found to be linear and the values of 0 have been extrapolated to zero concentration to give the °'8. For PAA and PMA, 0 °shows practically no dependence on the polymer molecular weight. The ®cp°'s have been found to be nonadditive, in contradistinction to what is observed with simple electrolytes. This result gives an additional experimental evidence to the so-called counterion "site binding." The volume changes associated with this process have been determined for various counterions and found to present large differences, according to the nature of both the polyion and the counterion. Finally for polycarboxylic acids simple assumptions have permitted the determination of the contribution of electrostriction to the apparent molal volume of the polyion at infinite dilution and of the fraction of bound counterions with total dehydration.

Precipitation−Redispersion of Cerium Oxide Nanoparticles with Poly(acrylic acid): Toward Stable Dispersions

“…We assume that the coated nanoparticles are of core-shell type, each compartment having an electronic densities CeO 2 and PAA 2 K . The excess of intensity as q 0 due to the PAA shell with respect to that of the bare particles reads [37,38] [39][40][41], and for the volume of an acrylate monomer v 0 = 54.8 Å 3 [42], ( V CeO 2 is calculated from the molecular weight), one ends up with a number of adsorbed polymers n ads = 34 ± 6. Both light and x-ray scattering experiments are in good agreement with each other and with the TOC results.…”

“…In a first case, we assume that all the acrylic acid monomers are adsorbed or in the close vicinity of the cerium oxide surfaces. With an average of 50 chains per particle and a monomeric molar volume v 0 = 54.8 Å 3 [42], a rapid estimate shows that the radius of the polymer-nanoparticle would then be increased by 0.4 nm. In a second case, we assume that the chains are attached by a few monomers and that the remaining part of the chain is highly stretched towards the surrounding solvent.…”

Evidence of overcharging in the complexation between oppositely charged polymers and surfactants

“…In the present model, the elementary scatterer comprises one aliphatic chain and counterions (Br -for DTAB and Na + for SDS). is the ratio (0 < < 1) of condensed counterions per surfactant molecule.For poly(acrylic acid) in its charged (as a sodium salt) and in its acidic forms, the apparent molal volumes have been measured consistently by different groups at 47.8 and 33 cm 3 ·mol -1 respectively 56,57 . These values were used in Table III (Table III).…”

On the Importance of Purification of Sodium Polystyrene Sulfonate

“…As Tondre and Zana [20] have pointed out, the removal of ionic impurities from the polyelectrolyte system is not possible by conventional solution and precipitation technique; for such system dialysis followed by ion exchange method is necessary. Indeed, several researchers [5,21,22] have employed ion exchange method for purification of NaPSS.…”