Effect of Charge Density on the Dynamic Behavior of Polyelectrolytes in Aqueous Solution

Abstract

Dynamic light scattering experiments and measurements of surface tension and viscosity of aqueous solutions of poly(2-vinylpyridine) quaternized with ethyl bromide are carried out as function of the charge density and polyelectrolyte concentration (Mw ) 2.9 × 10 5 , Mw/Mn ) 1.11; Re, degree of quaternization, 0.09 e Re e 0.46). The polyelectrolytes are dissolved in an aqueous solution of potassium bromide (cs ) 1 × 10 -2 c + , c + ) 1 mol dm -3 ). Their concentrations c jp are in the range 0.1c j + e c jp e 27c j + (c j + ) 1 g dm -3 ). The reduced variable Λ ()Recm/cs) is used to characterize the composition of the solutions (cm, molar volume concentration of the repeat unit of the polymer backbone). Monomodal and bimodal dynamic modes characterized by the apparent diffusion coefficients Ds and Df (index s, slow; index f, fast) are found under the following conditions: monomodal, 0.03 e Λ e 0.1; bimodal, 0.1 e Λ e 8. A third dynamic mode characterized by the apparent diffusion coefficient Dint (index int, intermediate) appears at Λ J 1 with small values of Re in the range 0.09 e Re e 0.15 (Ds < Dint < Df). It is assumed that the third mode reflects dynamic properties of hydrophobic domains formed by uncharged segments of the polymer backbone at low values of Re. Hydrophobic interactions show up also in surface tension and viscosity measurements. A model proposed by Lee and Schurr (J. Polym. Sci. 1975, 13, 873) describes the experimental Df data of the fast diffusive mode with two fit parameters (Zeff, effective number of charges of a polyion; Dp, diffusion coefficient of a polyion). Zeff is smaller by a factor of 5-7 than the value calculated on the basis of Re.

Dynamic light scattering and viscosimetry of aqueous solutions of pectin, sodium alginate and their mixtures: effects of added salt, concentration, counterions, temperature and chelating agent

“…17 Dynamic light scattering (DLS) studies on polyelectrolytes in the absence of salt or at low ionic strength show, in general, the existence of a bimodal time distribution behavior, corresponding to the existence of a fast and a slow relaxation mode. Such observations have been reported for different charged macromolecular systems, including synthetic [18][19][20][21][22] and biological polyelectrolyte solutions. [23][24][25] The fast mode is often interpreted as a process involving the diffusion of single polyions.…”

The slow relaxation mode: from solutions to gel networks

“…Gradually, such two modes have been reported for nearly all charged macromolecules, including both synthetic and biological polyelectrolytes in aqueous and nonaqueous solutions. [76][77][78][79][80][81][82][83][84] Therefore, these two modes are general features of salt-free or low-salt polyelectrolyte solutions. In the past, the fast mode in polymer dilute and semidilute solutions has been attributed to different origins, such as propagation of excitations in a polyelectrolyte pseudolattice or the free diffusion of the noncaged chains/particles.…”

“…The interpretation of the slow mode, especially for those very slow relaxation modes observed in salt-free or low-salt polyelectrolyte solutions, is very controversial. [76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95] It has been attributed to large multichain domains formed because of electrostatic interaction or some insoluble clusters or even a trace amount of dust particles introduced during the imperfect preparation of polymer solution. Actually, not everyone accepts or recognized such a slow mode, even though it has been repeatedly observed in many dynamic LLS experiments for more than three decades, because of some problems or questions related to previous light-scattering experiments, such as some earlier premature data analysis methods and the preparation of dust-free viscous solutions.…”

Characterization of Sodium Carboxymethyl Cellulose Aqueous Solutions to Support Complex Product Formulation: A Rheology and Light Scattering Study

“…23,58 Detailed discussions about the comparison between predicted and experimental values of Df can be found in the literature, such as a Sedlák and Amis' 57 about salt-free Na PSS solutions and Topp's about quaternized poly(2-vinylpyridine) in KBr solutions. 59 The slow mode is characterized by significantly longer relaxation times s, that are typically in the range of 1 ms to 10 s. 23,58 The slow mode has commonly been found to also exhibit a linear dependence in q 2 , 52,53,[55][56][57] for which a diffusion coefficient can be calculated 52 and an apparent hydrodynamic radius of the domains can be estimated. 52 However, other q-dependences have been observed for the slow mode 53,57 , where it has been suggested that the characteristic size of the domains, L, is large compared to the probed length scale so that qL >> 1 and internal relaxations within the domains are also probed.…”