Can Jones–Dole’s B-Coefficient be a Consistent Structure-Making/Breaking Marker? Rigorous Molecular-Based Analysis and Critical Assessment of Its Marker Uniqueness

Abstract

We analyzed the consistency, or lack thereof, of the conjectured connection between the sign of Jones−Dole's Bcoefficient, or its isobaric-temperature derivative, and the structure-making/breaking ability of a solute in a dilute solution. We sought to shed light on some crucial issues, including (i) whether Jones−Dole's B-coefficient contains any embedded microstructural information, (ii) whether we can either assign any definite foundation to the widely used assumption about the sign of the Bcoefficient and its structure-making/breaking trend or provide a rational justification for its use as a structure-making/breaking marker, and (iii) whether we actually need Jones−Dole's B-coefficient and its isobaric-temperature derivative as markers for the interpretation of structure-making/breaking trends. Thus, we first addressed the fundamental (statistical mechanical) microscopic to (thermodynamic) macroscopic foundations of a rigorous approach to the structure-making/breaking ability of a solute, regardless of the type of solvent or nature of the solute−solvent intermolecular interaction asymmetries, and its exact relationships to the resulting solution thermodynamics. Then, we derived the required conditions for the signs of the B-coefficient and/or its isobaric-temperature derivative to describe either a structure-making or a structure-breaking event, according to the actual solute-induced perturbation of the solvent microstructure, and consequently, tested the rationale underlying the B-based conjectured structure-making/breaking markers. Moreover, we invoked a well-known transition-state (TS) interpretation of the B-coefficient to connect it explicitly to the derived molecular-based structure-making/breaking signature and to find under which TS conditions the signs of the B-coefficient and its temperature derivative could describe the actual solute-induced perturbation of the solvent microstructure. We illustrated the actual structure-making/breaking behavior for a series of aqueous solutes over a wide range of solute−solvent intermolecular interaction asymmetries and compared their behavior against that predicted by Jones−Dole's based markers. This comparison, supported by rigorous thermodynamic arguments, highlighted the lack of uniqueness (or one-to-one correspondence) in the response of the B-based markers to the solute−solvent intermolecular interaction asymmetry, and therefore, their inadequacy as structure-making/breaking descriptors. Finally, we discuss the findings and provide a cautionary outlook on the use of the viscositybased structural markers.

On the Elusive Links between Solution Microstructure, Dynamics, and Solvation Thermodynamics: Demystifying the Path through a Bridge over Troubled Conjectures and Misinterpretations

“…Feakins’ TST formalism for the solute-induced effects on the transport properties of dilute solutions provides a more rigorous framework than the direct consideration of the B i – and B i ’ –coefficients, SI.105 and SI.116 in the section SI-8 of the Supporting Information, as well as their T – and P –derivatives . Yet, prior to drawing any conclusion from them, we should remember the empirical nature of SI.105 and the number of conjectured approximations behind SI.116 …”

“…Then, we proceed with the diffusion B i ' −coefficient counterpart , . As we have discussed elsewhere, 84 Feakins' TST interpretation of the B i −coefficient,…”

“…Indeed, any specific ion effect becomes always constrained by the electroneutrality (zeroth moment for each ion) and the Stillinger-Lovett (second moment) conditions for the ion–ion distribution functions , anion- and cation-specific effects cannot be treated as independent eventswhile simultaneously, the ion distributions are state condition and concentration dependent. In other words, any effort toward gaining insights into the electrolyte solute-induced effects through rules of thumb markers, including those based on the sign of either Jones–Dole’s viscosity B i – and Engel–Hertz’s diffusion B i ’ –coefficient of individual ions, or Hepler’s thermal expansivity of the salt, appears fruitless and misguided as critically discussed elsewhere. − …”

“…Feakins' TST formalism for the solute-induced effects on the transport properties of dilute solutions provides a more rigorous framework than the direct consideration of the B i − and B i ' −coefficients, SI.105 and SI.116 in the section SI-8 of the Supporting Information, as well as their T− and P−derivatives. 84 Yet, prior to drawing any conclusion from them, we should remember the empirical nature of SI.105 and the number of conjectured approximations behind SI.116. 140 In this section we take advantage of the sets of accurate experimental data from viscosity 81,141−143 as compiled in Tables 3−4 of Jenkins and Marcus' review 144 and nuclear magnetic relaxation time measurements 82,140,145,146 available in the current literature for a variety of dilute aqueous solutions covering a wide range of solute−solvent intermolecular interaction asymmetries.…”

“…84,87 By noticing that eqs 54 and 63 involve the same microstructural component, and consequently, the same f undamental structure making/breaking f unction ij , i.e.,…”