An Energetic Analysis of the Phase Separation in Non-Ionic Surfactant Mixtures: The Role of the Headgroup Structure

Abstract

Abstract:The main goal of this paper was to examine the effect of the hydrophilic surfactant headgroup on the phase behavior of non-ionic surfactant mixtures. Four mixed systems composed of an ethoxylated plus sugar-based surfactants, each having the same hydrophobic tail, were investigated. We found that the hydrophilicity of the surfactant inhibits the tendency of the system to phase separate, which is sensitive to the presence of NaCl. Applying a classical phase separation thermodynamic model, the corresponding energy parameters were evaluated. In all cases, the parameters were found to depend on the type of nonionic surfactant, its concentration in the micellar solution and the presence of NaCl in the medium. The experimental results can be explained by assuming the phase separation process takes place as a result of reduced hydration of the surfactant headgroup caused by a temperature increase. The enthalpy-entropy compensation plot exhibits excellent linearity. We found that all the mixed surfactant systems coincided on the same straight line, the compensation temperature being lower in the presence of NaCl.

Investigation of the Effect of Various Additives on the Clouding Behavior and Thermodynamics of Polyoxyethylene (20) Sorbitan Monooleate in Absence and Presence of Ceftriaxone Sodium Trihydrate Drug

“…34,35 The negative values of ΔH 0 c and ΔS 0 c point to the Negative values of ΔH 0 c and ΔS 0 c were also earlier observed for phase separation behavior of many non-ionic surfactant systems in aqueous condition as well as in the presence of NaCl. 36 Rub et al observed negative values of ΔH 0 c and ΔS 0 c for some amphiphilic drugs in the presence of Tween 80 and also other additives mixed systems. 33,37−40 The negative values of ΔH 0 c are indicative of an exothermic process.…”

“…For 2.00 × 10 –3 , 6 × 10 –3 , and 10.0 × 10 –3 mol·kg –1 Tween 80 solutions containing various concentrations of CFT solutions, the values of Δ H 0 c and Δ S 0 c are found to be negative at lower CFT concentration; the negative values are liable to decrease with the enhancement of CFT concentration. Negative values of Δ H 0 c and Δ S 0 c were also earlier observed for phase separation behavior of many non-ionic surfactant systems in aqueous condition as well as in the presence of NaCl . Rub et al observed negative values of Δ H 0 c and Δ S 0 c for some amphiphilic drugs in the presence of Tween 80 and also other additives mixed systems. ,− The negative values of Δ H 0 c are indicative of an exothermic process.…”

Phase Separation and Thermodynamic Behavior of Triton X-100 in the Occurrence of Levofloxacin Hemihydrates: Influence of Additives

“…The development of positive Δ H 0 c values is due to the disruption of the H 2 O structure around the nonpolar parts of the surfactant monomers . The negative values of Δ H 0 c indicate the existence of attractive forces (London dispersion forces) during the association of the surfactant systems, , while the positive magnitudes of Δ H 0 c indicate the destruction of the iceberg structure of H 2 O around the hydrophobic parts of the surfactants. − …”

Clouding and Thermodynamic Characteristics of Triton X-100 in the Presence of Ciprofloxacin Hydrochloride: Influence of Polyols

“…The positive value of Δ H c o is the outcome of the disruption of the H 2 O structure near the nonpolar parts of the surfactant, − whereas the negative Δ H c o value implies the presence of an attractive force such as London dispersion forces during surfactant association. , …”