Electrostatic Contributions to Chain Stiffness and Excluded-Volume Effects in Sodium Poly(2-acrylamido-2-methylpropanesulfonate) Solutions

Abstract

ABSTRACT:Chain stiffness and excluded-volume effects in 0.005-1 M aqueous NaCl solutions of sodium poly(2-acrylamido-2-methylpropanesulfonate) (Na PAMPS) at 25 C have been studied by viscometry on 15 samples with weight-average molecular weights of 1:7 Â 10 3 -7:1 Â 10 5 . The molecular weight dependence of intrinsic viscosity at each NaCl concentration C s is analyzed by a combination of Yoshizaki et al.'s theory for unperturbed wormlike chains and the quasi-two-parameter theory for excluded-volume effects to estimate the persistence length q and the excluded-volume strength B as functions of C s . Both q and its electrostatic contribution q el are close to the previously estimated values for Na poly(styrenesulfonate) (Na PSS) at the same C s , while B considerably differs between the two polymers. As was found for Na PSS, available polyelectrolyte theories fail to describe the C s -dependence of q el and B for Na PAMPS. The persistence length q of a polyelectrolyte, modeled by the wormlike chain, 1 in aqueous salt increases with lowering salt concentration C s , owing to enhanced electrostatic repulsion between neighboring charged groups of the chain.2-5 If the polyelectrolyte is intrinsically flexible, this increase in backbone stiffness is attended by chain expansion due to electrostatic excluded-volume interactions between charged groups distant along the chain contour. Thus, experimental studies of excluded-volume and stiffness effects are essential for our understanding of polyelectrolyte chains in solution. In practice, however, there is a great difficulty that the two effects affecting the molecular size in a similar manner can hardly be separated by experiment without resort to a relevant excluded-volume theory.In previous work, 6,7 we estimated q and B (the excluded-volume strength) for sodium poly(2-acrylamido-2-methylpropanesulfonate) (Na PAMPS), an intrinsically flexible polyelectrolyte, in 0.05 and 0.5 M aqueous NaCl from data for the intrinsic viscosity [], the mean-square radius of gyration, and the translational diffusion coefficient with the aid of the quasitwo-parameter (QTP) theory 8-10 for the wormlike chain or, more generally, the helical wormlike chain. 10 We found that this theoretical scheme for nonionic chains is capable of consistently describing excluded-volume effects on the three properties of the polymer in the aqueous salts. Thus the QTP theory should be useful for the study of dilute polyelectrolyte solutions unless C s is too low.The present work was undertaken to investigate the electrostatic contributions to chain stiffness and excluded-volume effects in aqueous NaCl solutions of Na PAMPS by viscometry. It is an extension of our previous studies on Na hyaluronte 11-14 (a weakly stiff polysaccharide) and Na poly(styrenesulfonate), [15][16][17] for which the ionic strength dependence of q and B was determined from measured [] with the aid of the QTP theory. In the work reported below, these parameters for Na PAMPS are estimated as functions of C s in the range from 0.005 to 1 M...

Intermolecular Interactions and Self-Assembly in Aqueous Solution of a Mixture of Anionic–Neutral and Cationic–Neutral Block Copolymers

“…This indicates that no phase separation takes place in their AP−MP mixture solutions. Yusa et al's 5 AP and MP samples have longer P block chains, so that the solubility of their AP and MP with the Avogadro constant N A , the classical electron radius a e (= 2.82 × 10 −13 cm), and the average contrast factor γ av (calculated from the measured or literature value 28 of the partial specific volume; see eq S4). At C S = 2 M, the profile shows essentially no angular dependence at k < 0.2 nm −1 , indicating that no large self-assemblies are formed in the mixture solution.…”

“…Figure compares SAXS profiles for aqueous solutions of the AP–MP mixture ( x + = 0.6) with c = 0.005 g/cm 3 at different NaCl molar concentrations C S . In the ordinate, K e is the optical constant defined by with the Avogadro constant N A , the classical electron radius a e (= 2.82 × 10 –13 cm), and the average contrast factor γ av (calculated from the measured or literature value of the partial specific volume; see eq S4). At C S = 2 M, the profile shows essentially no angular dependence at k < 0.2 nm –1 , indicating that no large self-assemblies are formed in the mixture solution.…”

Synthesis and Structural Analysis of Self-Associating Amphiphilic Statistical Copolymers in Aqueous Media

“…Since w slow , 1, we can approximate w fast M w,fast to M w,fast , and Table 2 lists the aggregation number M w,fast /M w of the fast- 19 (see above). This indicates that the major small aggregate of poly(NaAMPS/C 6 MA) takes a more compact conformation than the NaAMPS homopolymer does in aqueous NaCl presumably because of the hydrophobic interaction among C 6 MA monomer units within the aggregate.…”

Rheological scaling of ionic-liquid-based polyelectrolytes in ionic liquid solutions: the effect of the ion diameter of ionic liquids

“…However, eqn (1) may not be applicable at high c IL because, in reality, polyelectrolyte chains shrink and eventually reach the initial polyelectrolyte chain size at high c IL when the charge is completely screened. [28][29][30] Dobrynin and coworkers 31,32 have recently reported that the finite chain dimension of polyelectrolytes in the absence of electrostatics depends on chains persistent length and the second virial coefficient.…”