We demonstrate the potential to tune the binding of calcium ions with polystyrene sulfonate (PSS) in the presence of dodecyl sulfate (DS). This can aid the design of surfactantresponsive water-softening agents for applications in detergency. We use molecular dynamics simulations to study the effect of the concentration of DS ions and the degree of sulfonation on the propensity of calcium ions toward PSS. We observe that the presence of DS ions increases the propensity of calcium ions toward 100% sulfonated PSS. The above phenomenon is due to the hydrophobic attraction between PSS and DS at low DS concentrations and the formation of calcium ion bridges between sulfonate and sulfate groups at moderate to high DS concentrations. We also observe the formation of calcium ion bridges between the sulfonate groups at high DS concentrations. The presence of DS ions also increases the propensity of calcium ions toward 20% sulfonated PSS. This is mainly due to the hydrophobic attraction between PSS and DS ions. The calcium ion bridges between sulfonate and sulfate groups are less prevalent than those of 100% sulfonated PSS. We do not observe calcium ion bridges between sulfonate groups of 20% sulfonated PSS. We use the above-mentioned insights to suggest potential strategies for designing an anionic polyelectrolyte having a suitable calcium-binding ability at a given concentration of the anionic surfactant. Finally, strong PSS−DS affinity is detrimental to the activity of surfactants because less surfactant ions are available for detergency. Our results also indicate the possibility of altering the PSS−DS affinity by changing the degree of sulfonation.
The hardness-causing ions like calcium are detrimental to the performance of anionic surfactants like dodecyl sulfate. Polystyrene sulfonate is an essential component of ion exchange resins that are used to adsorb such ions. Therefore, understanding the binding behavior of calcium ions to polystyrene sulfonate in the presence of dodecyl sulfate is of industrial relevance. Two important structural parameters of polystyrene sulfonate are known to influence its behavior: (i) The arrangement of aromatic groups around the carbon backbone (tacticity) and (ii) the degree of sulfonation. We use molecular dynamics simulations to study the effect of the above two parameters on the calcium-binding to polystyrene sulfonate in the presence of dodecyl sulfate. We observe that the calcium-binding ability and its response to the dodecyl sulfate are highly sensitive to the arrangement of aromatic groups around the backbone. We identify one atactic structure of 100% sulfonated polystyrene sulfonate and another of 20% sulfonated polystyrene sulfonate that shows a significant increase in calcium ion binding upon the addition of dodecyl sulfate ions. The increase in the 100% sulfonated structure is due to the formation of calcium ion bridges between the sulfonate groups located on one side of the backbone. The increase in the 20% sulfonated structure is due to the increase in the sulfonate-Ca-Cl type of ion bridges. We also observe a stronger association between dodecyl sulfate and low sulfonated polystyrene sulfonate because of the hydrophobic interaction between polystyrene sulfonate's backbone and the hydrocarbon tail of dodecyl sulfate. However, aligning all the aromatic groups on the same side of the backbone (isotactic structure) sharply weakens the association between the two species. Our results can aid in achieving the desired water softening capacity of ion exchange resins in the presence of anionic surfactants via altering the tacticity and degree of sulfonation.
Calcium ions in hard water deteriorate the cleaning performance of detergents by interacting with the anionic surfactants and inducing their precipitation. Polystyrene sulfonate is a common component of cation-exchange resins that adsorb hard ions such as Ca+2 and Mg+2, which adhere to the sulfonate groups. Therefore, understanding the calcium-binding ability of polystyrene sulfonate in the presence of dodecyl sulfate can help in designing novel water-softening agents for applications related to detergency. Studying the association between polystyrene sulfonate and dodecyl sulfate via calcium ion bridges is also important. Since resins contain cross-linked polystyrene sulfonate, degrees of cross-linking and sulfonation are two important parameters. We use molecular dynamics simulations to study the effect of the above parameters on the calcium-binding ability of isotactic polystyrene sulfonate in the presence of dodecyl sulfate. We observe negligible dependence of calcium-ion binding of polystyrene sulfonate on the degrees of cross-linking and sulfonation. The formation of calcium ion bridges between cross-linked polystyrene sulfonate and dodecyl sulfate is strongly affected by the degree of sulfonation. Such bridges are observed more for the intermediate degrees of sulfonation. This is because, at a very low degree of sulfonation, dodecyl sulfate ions align closer to the cross-linking aromatic groups than the sulfonated ones. On the other hand, at high degrees of sulfonation, stronger electrostatic repulsion disfavors the proximity between dodecyl sulfate and polystyrene sulfonate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.