Effect of Acetonitrile and N,N-Dimethylformamide on the Formation of Poly(ethylene oxide)-Sodium Alkyl Sulfate Aggregates

Guilherme Ferreira,Ana Pires,Gabriel Ferreira,Jaqueline Rezende,Maria Hespanhol,Luis Silva,Álvaro Agudelo

doi:10.21577/0103-5053.20170111

Guilherme Ferreira, Ana Pires + Show 5 more

Open Access

https://doi.org/10.21577/0103-5053.20170111

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Abstract

The effects of low contents of acetonitrile (AN) or N,N-dimethylformamide (DMF) on the aggregation of sodium alkyl sulfate surfactants, in the absence and presence of poly(ethylene oxide) (PEO), were investigated using conductivity and isothermal titration calorimetry. The cosolvents slightly changed the critical micellar concentrations and did not alter the critical aggregation concentrations of the surfactants sodium decyl sulfate (DSS) and sodium dodecyl sulfate (SDS) with PEO. However, AN and DMF turned the micellization of the surfactants and their binding to the polymer enthalpically more favorable. For instance, for SDS, the micellization enthalpy, ΔHomic, decreased from close to 0 kJ mol-1 in water to -14.3 kJ mol-1 in the presence of 2.50 mol% AN, and the integral enthalpy change for aggregate formation with the polymer, ΔHagg(int), decreased from -1.1 kJ mol-1 in water to -15.5 kJ mol-1 in the same AN concentration. This was attributed to the modification of the solvation shells of both SDS and PEO by the cosolvent molecules, which reduced the entropic contribution to formation of the aggregates. Consequently, when SDS was replaced with DSS, the AN affected ΔHomic to a lesser extent, with a decrease of 9.1 kJ mol-1, while the ΔHagg(int) values were not altered, highlighting the influence of hydrophobic interactions in the surfactant aggregation process.

Highlights

Low contents of polar organic cosolvents such as acetonitrile and N,N-dimethylformamide can effectively modulate the solvent quality of water, altering the sodium dodecyl sulfate (SDS) and DSS surfactant aggregation properties in the presence of poly(ethylene oxide) (PEO)
In order to understand the effects of the cosolvents in this process, it is necessary to elucidate the ways that AN and DMF modify the delicate balance of intermolecular forces involved in the micellization of the surfactants
The presence of a single peak of low magnitude at 1.00 mol% AN indicated that the desolvation and re-solvation of both the SDS monomers and the PEO segments that took place during the interaction process mainly involved less structured water molecules around hydrophobic regions

Summary

Introduction

Properties of systems containing mixed surfactants and polymers are of great interest from both practical and theoretical perspectives, due to their various applications in separation,[1,2] dispersion,[3] and solubilization processes.[4,5,6] The properties of such systems can be improved by adding modifiers such as cosolvents,[7,8] cosurfactants,[9] electrolytes,[10,11] and ionic liquids.[12,13] studies of the effect of modifiers on polymer-surfactant systems have contributed to the understanding of the mechanisms involved in their aggregation, there is still insufficient information concerning the role of the solvent molecules in Extensive studies of water/AN mixtures have shown that the molecular microstructure in these solutions depends on the molar fraction of the cosolvent. In terms of the effects caused by the different cosolvents, the replacement of DMF by AN did not affect the magnitude of , but made more exothermic as the cosolvent concentration increased (Figure 2), showing that AN interacted more favorably with water molecules in the solvation shell of the surfactant chain.

Results

Conclusion