Microcalorimetric and SAXS Determination of PEO-SDS Interactions: The Effect of Cosolutes Formed by Ions

TL;DR

This study investigates how various ionic cosolutes affect PEO-SDS interactions using calorimetry and SAXS, revealing that some ions stabilize aggregates while others disrupt nanostructures, with detailed thermodynamic insights.

Contribution

It provides new insights into the influence of different ionic cosolutes on PEO-SDS interactions, combining calorimetric and SAXS techniques to elucidate structural and energetic effects.

Findings

NaCl, Na₂SO₄, Li₂SO₄, and NaSCN stabilize PEO-SDS aggregates at higher concentrations.

Na₂[Fe(CN)₅NO] disrupts PEO-SDS interactions and nanostructure formation.

Cosolutes can either stabilize or destabilize PEO-SDS interactions depending on their ionic nature.

Abstract

The effect of different ionic cosolutes (NaCl, Na$_2$SO$_4$, Li$_2$SO$_4$, NaSCN, Na$_2$[Fe(CN)5NO], and Na$_3$[Co(NO)$_6$]) on the interaction between sodium dodecyl sulfate (SDS) and poly(ethylene oxide) (PEO) was examined by small-angle X-ray scattering (SAXS) and isothermal titration calorimetric techniques. The critical aggregation concentration values (cac), the saturation concentration ($C_2$), the integral enthalpy change for aggregate formation ($\Delta H_{\mbox{agg}}$(int)) and the standard free energy change of micelle adsorption on the macromolecule chain ( $\Delta\Delta G_{\mbox{agg}}$) were derived from the calorimetric titration curves. In the presence of 1.00 mmol L$^{-1}$ cosolute, no changes in the parameters were observed when compared with those obtained for SDS-PEO interactions in pure water. For NaCl, Na$_2$SO$_4$, Li$_2$SO$_4$, and NaSCN at 10.0 and 100 mmol L$^{-1}$, the cosolute presence lowered cac, increased $C_2$, and the PEO-SDS aggregate became more stable. In the presence of Na$_2$[Fe(CN)5NO], the calorimetric titration curves changed drastically, showing a possible reduction in the PEO-SDS degree of interaction, possibility disrupting the formed nanostructure; however, the SAXS data confirmed, independent of the small energy observed, the presence of aggregates adsorbed on the polymer chain.