Structure and dynamics of atactic Na+-poly(acrylic) acid (PAA) polyelectrolyte in aqueous solution in dilute, semi-dilute and concentrated regimes
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...
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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
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
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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
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
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TL;DR: In this article, molecular dynamic simulations of anionic polyelectrolyte poly(acrylic acid) (PAA) in water-ethanol solution were carried out across the solvent composition range 0.
Abstract: Molecular dynamic simulations of anionic polyelectrolyte poly(acrylic acid) (PAA) in water–ethanol solution, specifically Li+-PAA and Cs+-PAA, were carried out across the solvent composition range 0 ≤ фeth ≤ 0.9. Chain collapse (i.e. shrinkage) occurs with increase in фeth for both types of counter-ion systems and in agreement with the experiments. The qualitative difference in the collapse point is in agreement with experimental results, with counter-ion specific chain collapse of PAA following the order Li+ > Cs+. With increase in фeth the number of hydrogen-bonds between PAA and water decreases while that between PAA and ethanol increases. At higher level of ethanol content in solution, ethanol molecules displace water molecules from the vicinity of the chain. The analysis of the radial distribution functions shows that counter-ion binding distance of Li+ to chain is lesser as compared to that of Cs+, as well as a higher coordination number exhibited by Li+. Thus, as compared to Cs+-PAA, greate...
19 citations
"Structure and dynamics of atactic N..." refers background or methods or result in this paper
...The self-diffusion coefficient for PAA chain and Na counterions were estimated using the Einstein relation [57]...
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...SPC/E provides more accurate results as compared to SPC as shown by our previous work [57]....
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...In our previous studies reported in the literature [16, 24, 57] for polycarboxylate type anionic polyelectrolyte such as PMA and PAA containing 30-mer single chains, multiple initial conformations for each tactcity sequence were simulated in very dilute concentration regime (single chain system) and no appreciable difference in results were found....
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...of such polymers [24,28,50,57] and multi-chain solutions [16,25,51] of polycarboxylate type of polyelectrolytes in...
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...was subjected to potential-energy minimisation using the Steepest-Descent method [50,51,57]....
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TL;DR: In this article, small-angle X-ray scattering (SAXS) was used to obtain solution parameters of a weak polyelectrolyte in water in the absence of any additives, such as neutralizing agents or salt.
Abstract: Small-angle X-ray scattering (SAXS) was used to obtain solution parameters of a weak polyelectrolyte in water in the absence of any additives, such as neutralizing agents or salt. Poly(acrylic acid) (PAA) was used as a weak polyelectrolyte from which SAXS data were obtained in the dilute region of 1-10 mg cm -3 . An intrinsic viscosity of 15.7 dL g -1 was obtained from a plot of reciprocal reduced viscosities versus the concentration. The application of the SAXS data, that is, the contour length (L = 1.97 x 10 4 A), the persistence length (a* = 58.5 A), and the molecular weight (M = 5.9 x 10 5 Da), to the Yamakawa-Fujii equation suggested that PAA in water at 25 °C could be described as a wormlike chain having a cylindrical body of d = 6 A. An end-to-end distance (r = 1.6 x 10 3 A) was calculated from r = 2a*L - 2(a*) 2 . The nonisotropic expansion factor (α = 2.9) was calculated for PAA expanding from the random coil in dioxane at 30 °C Θ) temperature) to the wormlike chain in water at 25 °C.
16 citations
"Structure and dynamics of atactic N..." refers methods in this paper
...increase in polymer concentration (Cp), as shown by smallangle X-ray scattering experiments [27]....
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15 citations
14 citations
"Structure and dynamics of atactic N..." refers result in this paper
...Our results are also in qualitative agreement with results of Na ion self-diffusion coefficient measurements of sodium i-carrageenan, and sodium dextran sulphate, which showed decrease in self-diffusion coefficient for Na with increase in polyion concentration [81]....
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TL;DR: In this article, the authors studied the dynamic behavior of chain conformations, hydrogen bonds and translational diffusion of aqueous poly(methacrylic acid) (PMA) solution as a function of polymer volume fraction Φp across dilute to concentrated regimes, including pure polymer amorphous state.
Abstract: The dynamic behaviour of chain conformations, hydrogen bonds and translational diffusion of aqueous poly(methacrylic acid) (PMA) solution as a function of polymer volume fraction Φp across dilute to concentrated regimes inclusive of the pure polymer amorphous state was studied by molecular dynamics simulations. The behaviour of the relaxation time (τ) of the backbone dihedral angle auto-correlation function (ACF) reveals slower relaxation at higher level of polymer concentration and the existence of a concentration-driven relaxation transition for the aqueous polymer solution which occurs in the polymer volume fraction range, specifically 54% < Φp < 82% for this system. The relaxation constant τ for backbone dihedral angle exhibits a linear variation with Φp, indicating a first-order kinetic transition. The intermittent ACF for decay of the H-bond correlation shows that H-bonds among water molecules relax faster than those of the PMA–PMA and PMA–water type. The relaxation rate of PMA–water H-bonds shows a...
14 citations
"Structure and dynamics of atactic N..." refers background or methods or result in this paper
...fp in agreement with the observation made in previous works [16,51] that bound water content increases with fp in semidilute and concentrated regimes....
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...The use of the GROMOS force field (FF) has given good results for atomistic MD simulation studies of PAA and other anionic polyelectrolytes in aqueous solutions [16,25,28,50,51]....
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...of such polymers [24,28,50,57] and multi-chain solutions [16,25,51] of polycarboxylate type of polyelectrolytes in...
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...was subjected to potential-energy minimisation using the Steepest-Descent method [50,51,57]....
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...In our previous studies reported for multiple chain systems, simulations were performed on samples having different initial conformations of anionic polyelectrolytes PMA and PEA but it was found that the results remain unchanged and that they do not improved the statistical accuracy of the properties [16,25,51]....
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