Abstract
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.
Highlights
Soluble polymers can significantly improve solid–liquid separation processes and are increasingly used in various industries, including mineral recovery, papermaking, wastewater treatment, and dewatering of mining tailings [1,2,3]
The radius of gyration (Rg) directly indicates the degree of coiling that a molecule has by measuring the distance that the atoms of the molecule have with respect to its center of mass
When the concentration of salt increases, a slight increase in Rg is observed, but even so, it stays within a value of the radius of gyration of 1.1 nm
Summary
Soluble polymers can significantly improve solid–liquid separation processes and are increasingly used in various industries, including mineral recovery, papermaking, wastewater treatment, and dewatering of mining tailings [1,2,3]. It is attractive to look for new soluble polymers that preserve their extension in solution, even in low-quality water, which could have significant benefits on mineral flocculation, such as quartz and clays In this context, PAM derivatives such as poly (2-acrylamido-2-methylpropanesulfonate) polyelectrolyte (PAMPS), have been used in extreme saline brines as a stabilizer in silica nanoparticle coating due to the synergistic action between strong sulfonate groups and hydrophilic amide groups [20,21] and anticoagulant applications [22]. Ma and Pawlik [33] studied the effect of different monovalent cations, proposing that this polymer competes with water to access the silanol sites on the quartz surface This represents a new research opportunity, which is addressed in the present research, aiming to improve the understanding of conformation, counterion condensation, and water structure of polymers in saline solutions. The SPC/E water model [42] was used in conjunction with the SETTLE constraints for the molecule’s geometry [43]
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