Molecular dynamics simulations of the conformation and diffusion of partially hydrolyzed polyacrylamide in highly saline solutions

Quezada, Gonzalo R.; Saavedra, Jorge H.; Rozas, Roberto; Toledo, Pedro G.

doi:10.1016/j.ces.2019.115366

Cited by 25 publications

(25 citation statements)

References 58 publications

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“…in the corundum (−0.20 C/m 2 vs −0.110 C/m 2 ) . The cation adsorption sequences on kaolinite edge surfaces, as in (001) corundum surfaces, are well-known and have been satisfactorily explained by a “like absorbs like” concept, that is, high isoelectric point materials preferentially adsorb well-hydrated cations. − …”

Section: Resultsmentioning

confidence: 99%

Ab Initio Calculations of Partial Charges at Kaolinite Edge Sites and Molecular Dynamics Simulations of Cation Adsorption in Saline Solutions at and above the pH of Zero Charge

2019

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Molecular dynamics simulations are used to study adsorption of cations on the (010) kaolinite edge surface at and above the pH of zero charge. The cation solutions are highly concentrated and include alkali and alkaline-earth metals. It is known that the pH-dependent edge surface of kaolinite is more reactive than the basal surfaces and more eager to adsorb metal ions; however, knowledge of the atomic scale is scarce regarding the structure of the surface edge, charge distribution, solvation, and structure of layers of adsorbed cations. First, ab initio calculations are used to determine the energetically most favorable surface terminations and the distribution of partial atomic charges on both neutral (protonated) and negatively charged (deprotonated) edge surfaces of kaolinite. Then, molecular dynamics simulations are used to study the solvation of kaolinite and the adsorption of cations. Results include density profiles of adsorbed cations, orientation profiles of water molecules close to the mineral surface for different cations, and the distance at which such surfaces become neutral or reverse their charges. Results compare well with available experimental and simulation data. Findings are expected to contribute to the selection or design of organic compounds that effectively adhere to kaolinite in aqueous electrolyte solutions in water recovery processes.

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Section: Resultsmentioning

confidence: 99%

Ab Initio Calculations of Partial Charges at Kaolinite Edge Sites and Molecular Dynamics Simulations of Cation Adsorption in Saline Solutions at and above the pH of Zero Charge

2019

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“…For the HPAM and PAMPS molecules, there is an increase in the frequency values of −0.6 and −1.0. This indicates that the orientation of the hydrogens is stronger because, at cos(ϕ) equal to −0.6, the hydrogen atom is in direct line with polymer atoms [ 53 ] while, at −1.0, both hydrogens are oriented to the atoms of the polymer. The ability to orient the water molecules of HPAM is greater than PAMPS because the SO 3 groups are weaker than the COO.…”

Section: Resultsmentioning

confidence: 99%

Molecular Dynamics Study of the Conformation, Ion Adsorption, Diffusion, and Water Structure of Soluble Polymers in Saline Solutions

et al. 2021

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Polymers have interesting physicochemical characteristics such as charge density, functionalities, and molecular weight. Such attributes are of great importance for use in industrial purposes. Understanding how these characteristics are affected is still complex, but with the help of molecular dynamics (MD) and quantum calculations (QM), it is possible to understand the behavior of polymers at the molecular level with great consistency. This study was applied to polymers derived from polyacrylamide (PAM) due to its great use in various industries. The polymers studied include hydrolyzed polyacrylamide (HPAM), poly (2-acrylamido-2-methylpropanesulfonate) (PAMPS), polyacrylic acid (PAA), polyethylene oxide polymer (PEO), and guar gum polysaccharide (GUAR). Each one has different attributes, which help in understanding the effects on the polymer and the medium in which it is applied along a broad spectrum. The results include the conformation, diffusion, ion condensation, the structure of the water around the polymer, and interatomic polymer interactions. Such characteristics are important to selecting a polymer depending on the environment in which it is found and its purpose. The effect caused by salinity is particular to each polymer, where polymers with an explicit charge or polyelectrolytes are more susceptible to changes due to salinity, increasing their coiling and reducing their mobility in solution. This naturally reduces its ability to form polymeric bridges due to having a polymer with a smaller gyration radius. In contrast, neutral polymers are less affected in their structure, making them favorable in media with high ionic charges.

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“…A possible explanation for the observed high-concentration dynamics could be a slowdown in the solvent diffusion with increasing polymer concentrations. This phenomenon has been observed for many polymer–solvent systems and might be particularly strong for polyelectrolytes due to the ordering of water around the ionic groups. − In this scenario, the scaling laws outlined in Section 2.1 need to be applied with β( c ) > η s . Mackie et al’s obstruction model expects the solvent diffusion coefficient ( D s ) to depend on the polymer volume fraction (ϕ) as Equation has been shown to correctly describe the dependence of D s on polymer concentration for many polymer–solvent pairs, including polyelectrolytes .…”

Section: Discussionmentioning

confidence: 99%

Diffusion and Viscosity of Unentangled Polyelectrolytes

et al. 2021

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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 molecular weight of NaPSS is characterized using five techniques. Relationships between M w and the intrinsic viscosity and diffusion coefficient in excess salt are established. These are helpful for the accurate determination of the molar mass of NaPSS. The observed concentration dependence of η and D are consistent with the Rouse–Zimm scaling model if the monomeric friction coefficient (ζ) is concentration-dependent. The concentration dependence of ζ exceeds that expected from free-volume models of diffusion, and its origin remains unclear, possibly being related to electrostatic effects. Correlation blobs and dilute chains with equivalent end-to-end distances exhibit nearly equal friction coefficients, in agreement with scaling. Viscosity and diffusion data are combined using the Rouse model to calculate the single-chain dimensions of NaPSS in salt-free solution, and the results overpredict direct SANS measurements of the radii of gyration by a factor of ≃1.4.

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Molecular dynamics simulations of the conformation and diffusion of partially hydrolyzed polyacrylamide in highly saline solutions

Cited by 25 publications

References 58 publications

Ab Initio Calculations of Partial Charges at Kaolinite Edge Sites and Molecular Dynamics Simulations of Cation Adsorption in Saline Solutions at and above the pH of Zero Charge

Ab Initio Calculations of Partial Charges at Kaolinite Edge Sites and Molecular Dynamics Simulations of Cation Adsorption in Saline Solutions at and above the pH of Zero Charge

Molecular Dynamics Study of the Conformation, Ion Adsorption, Diffusion, and Water Structure of Soluble Polymers in Saline Solutions

Diffusion and Viscosity of Unentangled Polyelectrolytes

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