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

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, , 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, ΔH agg (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 to a lesser extent, with a decrease of 9.1 kJ mol -1 , while the ΔH agg (int) values were not altered, highlighting the influence of hydrophobic interactions in the surfactant aggregation process.

Total Description of Intrinsic Amphiphile Aggregation: Calorimetry Study and Molecular Probing

“…Cosolvents such as acetonitrile (MeCN) have been used for changing the solvation of surfactants and thus alter the micellization equilibrium. − …”

Thermodynamics of Aggregation between the Cationic Surfactant and Polymer Based on Biodegradable Poly(vinyl Alcohol)

“…The complex profile of the curve suggests the occurrence of different molecular events involving the aggregation process of the surfactant on the macromolecular chain as the C 16 PyCl concentration increased. Probably, this profile could be associated with the reorganization of the C 16 Py + monomers on the macromolecular chains since it has been already pointed out for other nonionic polymer–surfactant systems: at low surfactant concentrations, in which the interaction occurs, the monomers are bound individually to the macromolecules. Then, as the surfactant concentration was increased, monomers of surfactant began to form small aggregates anchored on the polymer, which promoted a partial rehydration of the PVOH polymer chains, decreasing Δ H ap‑int (first endothermic peak).…”

“…Previous studies have proposed that in the region between cac and C2, the surfactant spontaneously interacts with the polymer, forming surfactant–polymer aggregates in the solution. − Considering the processes occurring in the PVOH aqueous solution for lower surfactant concentrations, as the C 16 PyCl concentration increased, the addition of monomers of C 16 PyCl in the system concentrated in the bulk solution and in the air–solution interface up to the concentration reaching the cac, in which the surfactant–PVOH aggregates began to be formed. The amount of the surfactant bound to the polymer increased as C C16PyCl increased until C2 was reached, in which the energetic saturation of PVOH macromolecules occurred, forming free micelles of C 16 PyCl in the solution.…”

Filmes Biodegradáveis Formados Por Taninos Condensados E Álcool Polivinílico Modificado

“…Entretanto, com o aumento da concentração a partir de 0,125% m/v, o aumento da turbidez sugere o início da interação. Esse processo é similar a outros processos cooperativos, como o processo envolvendo formação de micelas de surfactante e a agregação entre polímeros e surfactantes, que ocorrem por meio de interações hidrofóbicas, ou seja, interações que ocorrem pelo aumento da entropia do sistema (FERREIRA et al, 2017). Baseados nos estudos de turbidez em função da concentração, outras concentrações de polímero precisam ser investigadas para avaliar o efeito de turbidez e precipitação, levando a uma melhor possibilidade de escolha da mistura para formação dos filmes.…”