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

Aparecida Mageste Barbosa; Igor José Boggione Santos; Guilherme Max Dias Ferreira; Maria do Carmo Hespanhol da Silva; Alvaro Vianna Novaes de Carvalho Teixeira; Luis Henrique Mendes da Silva

doi:10.1021/jp1032178

paper

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

arXiv:1409.0115 · doi:10.1021/jp1032178

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 ($ΔH_{\mbox{agg}}$(int)) and the standard free energy change of micelle adsorption on the macromolecule chain ( $ΔΔG_{\mbox{agg}}$) 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.

8 pages, 8 figures