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Journal ArticleDOI

Structure and dynamics of atactic Na+-poly(acrylic) acid (PAA) polyelectrolyte in aqueous solution in dilute, semi-dilute and concentrated regimes

14 May 2019-Molecular Simulation (Taylor & Francis)-Vol. 45, Iss: 11, pp 876-895
TL;DR: In this paper, structural and dynamic properties of aqueous solution of atactic poly(acrylic) acid in dilute, semi-dilute and concentrated regimes were studied by fully atomistic molecular dynamics simulati...
Abstract: Structural and dynamic properties of aqueous solution of atactic poly(acrylic) acid (PAA) in dilute, semi-dilute and concentrated regimes were studied by fully atomistic molecular dynamics simulati...
Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors investigate theoretically charge regulation of weakly dissociating polyacids by potentiometric titration of their aqueous solutions, by treating deprotonation and cation binding to the polyacid as reversible reactions in their model, the ionization constant of acid groups along the polyacid chain is adjusted from its intrinsic value by electrostatic correlations.

20 citations

Journal ArticleDOI
TL;DR: It is observed that at low polymer concentrations PDMAEMA chains adopt a stiffer and slightly extended conformation due to excluded-volume effects and electrostatic repulsions within the polymer chains, as the polymer concentration increases above 20 wt %, and adopt more flexible conformations.
Abstract: A combined experimental and molecular dynamics (MD) study is performed to investigate the effect of polymer concentration on the zero shear rate viscosity η0 of a salt-free aqueous solution of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), a flexible thermoresponsive weak polyelectrolyte with a bulky 3-methyl-1,1-diphenylpentyl unit as the terminal group. The study is carried out at room temperature (T = 298 K) with relatively short PDMAEMA chains (each containing N = 20 monomers or repeat units) at a fixed degree of ionization (α+ = 100%). For the MD simulations, a thorough validation of several molecular mechanics force fields is first undertaken for assessing their capability to accurately reproduce the experimental observations and established theoretical laws. The generalized Amber force field in combination with the restrained electrostatic potential charge fitting method is eventually adopted. Three characteristic concentration regimes are considered: the dilute (from 5 to 10 wt %), the semidilute (from 10 to 20 wt %), and the concentrated (from 20 to 29 wt %); the latter two are characterized by polymer concentrations cp higher than the characteristic overlap concentration cp*. The structural behavior of the PDMAEMA chains in the solution is assessed by calculating the square root of their mean-square radius of gyration «Rg 2»0.5, the square root of the average square chain end-to-end distance «Ree 2»0.5, the ratio «Ree 2»/«Rg 2», and the persistence length Lp. It is observed that at low polymer concentrations, PDMAEMA chains adopt a stiffer and slightly extended conformation because of excluded-volume effects (a good solvent is considered in this study) and electrostatic repulsions within the polymer chains. As the polymer concentration increases above 20 wt %, the PDMAEMA chains adopt more flexible conformations, as the excluded-volume effects seize and the charge repulsion within the polymer chains subsides. The effect of total polymer concentration on PDMAEMA chain dynamics in the solution is assessed by calculating the orientational relaxation time τc of the chain, the center-of-mass diffusion coefficient D, and the zero shear rate viscosity η0; the latter is also measured experimentally here and found to be in excellent agreement with the MD predictions.

13 citations

Posted Content
TL;DR: In this paper, the authors reported self-diffusion and viscosity data for sodium polystyrene sulfonate (NaPSS) in semidilute salt-free aqueous solutions measured by pulsed field gradient NMR and rotational rheometry respectively.
Abstract: We report chain self-diffusion and viscosity data for sodium polystyrene sulfonate (NaPSS) in semidilute salt-free aqueous solutions measured by pulsed field gradient NMR and rotational rheometry respectively. The observed concentration dependence of $\eta$ and $D$ are consistent with the Rouse-Zimm scaling model with a concentration dependent monomeric friction coefficient. The concentration dependence of the monomeric friction coefficient exceeds that expected from free-volume models of diffusion, and its origin remains unclear. Correlation blobs and dilute chains with equivalent end-to-end distances exhibit nearly equal friction coefficients, in agreement with scaling. The viscosity and diffusion data are combined using the Rouse model to calculate the chain dimensions of NaPSS in salt-free solution, these agree quantitatively with SANS measurements.

11 citations

Journal ArticleDOI
TL;DR: Molecular dynamics simulations are used to study structure and dynamics of poly(vinyl alcohol) and water in aqueous solution as a function ofconcentration at different temperatures in the range 278.
Abstract: Molecular dynamics simulations are used to study structure and dynamics of poly(vinyl alcohol) and water in aqueous solution as a function ofconcentration at different temperatures in the range 278...

5 citations

References
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Journal ArticleDOI
01 May 1987-Polymer
TL;DR: In this paper, photon correlation spectroscopy was used to investigate the diffusion of poly(methacrylic acid) in salt-free solutions of polyelectrolytes.

96 citations


"Structure and dynamics of atactic N..." refers background in this paper

  • ...degree-of-ionisation) was observed [36]....

    [...]

  • ...The concentration dependence of the diffusion coefficient of PMA in aqueous solution, as determined by dynamic light scattering experiments, showed that the diffusivity of PMA decreases linearly with concentration [36]....

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Journal ArticleDOI
TL;DR: In this paper, the results of molecular dynamics simulations of polyelectrolyte solutions in near-ϑ-solvent conditions for polymer backbone were presented, and the simulation results for chain size dependence on the degree of polymerization at different polymer concentrations were in good qualitative agreement with predictions of the modified scaling model that takes into account nonuniform stretching of polyethylte chains.
Abstract: We present the results of molecular dynamics simulations of polyelectrolyte solutions in near-ϑ-solvent conditions for polymer backbone. Polyelectrolyte solutions are modeled as an ensemble of bead-spring chains of charged Lennard-Jones particles with explicit counterions. Simulations were performed for both fully and partially charged polyelectrolyte chains with the number of monomers N varying from 25 to 300 in the range of polymer concentrations covering both dilute and semidilute regime. Polyelectrolyte chains in dilute solutions are nonuniformly stretched with the projection of the linear monomer density onto the end-to-end vector increasing logarithmically from the middle of the chain. The simulation results for chain size dependence on the degree of polymerization at different polymer concentrations are in good qualitative agreement with predictions of the modified scaling model that takes into account nonuniform stretching of polyelectrolyte chains. In semidilute solutions we confirm that the corr...

88 citations

Journal ArticleDOI
TL;DR: Structural changes behind alterations in enzyme activity in water-ethanol mixtures have been studied by the method of circular dichroism and structural changes in the protein have been observed for different forms of CT that were well correlated with a decrease in enzymatic activity.
Abstract: Formation of noncovalent complexes between α-chymotrypsin (CT) and a polyelectrolyte, polybrene (PB), has been shown to produce two major effects on enzymatic reactions in binary mixtures of polar organic cosolvents with water. (i) At moderate concentrations of organic cosolvents (10% to 30% v/v), enzymatic activity of CT is higher than in aqueous solutions, and this activation effect is more significant for CT in complex with PB (5- to 7-fold) than for free enzyme (1.5- to 2.5-fold). (ii) The range of cosolvent concentrations that the enzyme tolerates without complete loss of catalytic activity is much broader. For enhancement of enzyme stability in the complex with the polycation, the number of negatively charged groups in the protein has been artificially increased by using chemical modification with pyromellitic and succinic anhydrides. Additional activation effect at moderate concentrations of ethanol and enhanced resistance of the enzyme toward inactivation at high concentrations of the organic solvent have been observed for the modified preparations of CT in the complex with PB as compared with an analogous complex of the native enzyme. Structural changes behind alterations in enzyme activity in water-ethanol mixtures have been studied by the method of circular dichroism (CD). Protein conformation of all CT preparations has not changed significantly up to 30% v/v of ethanol where activation effects in enzymatic catalysis were most pronounced. At higher concentrations of ethanol, structural changes in the protein have been observed for different forms of CT that were well correlated with a decrease in enzymatic activity. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng55: 267–277, 1997.

76 citations

Journal ArticleDOI
TL;DR: The results illustrate the utility of the FCS technique for studying hydrodynamic sizes of polyelectrolyte coils in response to variation in solution pH or concentration of salt and poly electrolytes and suggest that FCS will be a promising technique for selective observation of the dynamics of polyElectrolye components in complex polymer mixtures.
Abstract: We apply fluorescent correlation spectroscopy (FCS) to investigate solution dynamics of a synthetic polyelectrolyte, i.e., a weak polycarboxylic acid in aqueous solutions. The technique brings single molecule sensitivity and molecular specificity to dynamic measurements of polyelectrolyte solutions. Translational diffusion of Alexa-labeled poly(methacrylic acid), PMAA*, chains was studied in very dilute, 10−4 mg/ml, solutions as a function of solution pH and ionic strength. The observed changes in diffusion coefficients were consistent with about twofold expansion of PMAA* coils when pH was changed from 5 to 8, and with chain contraction for alkaline metal ion concentrations from 0.01 to 0.1 M. The dependence of the hydrodynamic size of PMAA* chains on the counterion type followed the sequence: Li+>Na+≈Cs+>K+. The dependence of translational diffusion on polyacid concentration was weak at the low concentration limit, but chain motions were significantly slower at higher polymer concentrations when PMAA chains overlapped. Finally, measurements of dynamics of PMAA* chains in “salt-free” solutions showed that self-diffusion of PMAA* chains significantly slowed down when PMAA concentration was increased, probably reflecting the sensitivity of PMAA* translational motions to the onset of interchain domain formation. These results illustrate the utility of the FCS technique for studying hydrodynamic sizes of polyelectrolyte coils in response to variation in solution pH or concentration of salt and polyelectrolytes. They also suggest that FCS will be a promising technique for selective observation of the dynamics of polyelectrolyte components in complex polymer mixtures.

74 citations


"Structure and dynamics of atactic N..." refers background in this paper

  • ...with polymer concentration in salt-free aqueous solutions [87]....

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