Specific Salt Effects on Poly(ethylene oxide) Electrolyte Solutions

Abstract

Exploring the mechanism of specific salt effects in electrolyte solutions is an old and attractive subject. It has been gradually realized that the competition at the molecular level plays an important role. Aiming to include molecular details as many as possible, we combine molecular dynamics (MD) simulations with a molecular theory to study specific salt effects on poly(ethylene oxide) (PEO) solutions with the addition of monovalent salt. Radial distribution functions obtained from MD simulations provide microscopic structures of different components as well as interactions between various species. On the basis of these interactions, we construct the molecular theory with four assumptions: (1) an ion along with bound water in the first shell works as a single entity; (2) short-ranged interactions among various species are modeled as hydrogen-bonding interactions; (3) the ability of a hydrated ion to provide donors/acceptors for hydrogen bonding is governed by the charge density; (4) contact ion pairs are included, especially in the cases of small cations. The molecular theory is generalized with the explicit inclusion of ion-PEO, ion-water, ion-ion, water-water, and water-PEO hydrogen bonds. This means the molecular-scale structure and interaction are included within the frame of the theory. Theoretically calculated cloud points verify that the salting-out ability for alkali metal ions follows the series ofwhich is in agreement with the experimental observations. Here, the competition among ion-PEO, ion-water, and water-PEO interactions and the impact of steric repulsions induced by the introduction of ions are two essential factors determining the phase behavior of PEO solutions. The combined methods bridge the microscopic interactions and structures to the macroscopic behavior.

Pressure-Stimulated Supercrystal Formation in Nanoparticle Suspensions

“…This points to specifics of the PEG-cation interaction: The salting-out-capability trend based on theoretical calculations proposed by Ren et al follows the trend K + > Rb + > Cs + > Na + , which is in better agreement with our experimental findings. 33 When mixing the AuNP@PEG with 1 M CaCl 2 no crystal formation was observed within the pressure range studied, whereas for the sulfate salt K 2 SO 4 , crystallites with fcc structure, although less defined, were already formed at ambient conditions (Fig. S4-S5).…”

A vertical lamellae arrangement of sub-16 nm pitch (domain spacing) in a microphase separated PS-b-PEO thin film by salt addition

“…[18][19][20][21][22] Importantly, the high affinity of the ethyleneoxy segments for various cations allows this system to be used as templates for inorganic pattern development in various lithographic and biological applications [23][24][25][26] . The polystyrene-b-polyethylene oxide (PS-b-PEO) system is an attractive alternative to PS-b-PMMA and the asymmetric, cylinder forming compositions have been well researched and exhibits high degrees of lateral ordering within short processing times without any substrate surface modification.…”

Influence of Specific Anions on the Orientational Ordering of Thermotropic Liquid Crystals at Aqueous Interfaces

“…1 At elevated concentrations, in particular, ion-specific effects are evident in a wide variety of biological and physiochemical phenomena 2–6 including measurements of protein stability, 1, 7–10 micelle formation, 10–13 polymer behavior, 14–16 and colloidal aggregation. 17–20 In early studies, salts were ranked and classified according to their tendency to stabilize or destabilize the native structure of proteins, leading to the naming of some ions as kosmotropes (generally small and strongly hydrated ions) and others as chaotropes (large and weakly hydrated ions).…”