The selective partitioning of the oligomers of polyethoxylated surfactant mixtures between interface and oil and water bulk phases

A methodology for measuring the characteristic curvature of technical-grade ethoxylated nonionic surfactants: the effects of concentration and dilution

Characterization of the behaviour of commercially available non-ionic surfactants has received considerable attention due to their efficacy in a variety of applications. The main challenge in the application of these types of surfactants is that the hydrophilicity of the surfactant varies with concentration and dilution due to the polydispersity of the ethylene oxide groups. The hydrophilicity of a surfactant can be quantified by the characteristic curvature (Cc) parameter of the hydrophilic–lipophilic difference (HLD) framework. In this work, a model based on natural logarithmic regression was developed to calculate the Cc value of commercial surfactants as a function of surfactant concentration by a fast and simple phase scan. The slope of the Cc curve and the measured Cc at a reference concentration were used to develop the model. The Cc values determined with the model agreed with the measured values from the phase scans. Furthermore, the linear mixing rule proved to be reliable for mixtures of polydisperse ethoxylated surfactants. Finally, the impact of the water-to-oil ratio on the Cc was evaluated and the implications were discussed.

The Salinity-Phase-Inversion method (SPI-slope): A straightforward experimental approach to assess the hydrophilic-lipophilic-ratio and the salt-sensitivity of surfactants

HYPOTHESIS

The salinity at which the dynamic phase inversion of the reference system C₁₀E₄/n-Octane/Water occurs in the presence of increasing amounts of a test surfactant S₂ provides quantitative information on the hydrophilic/lipophilic ratio and on the sensitivity to NaCl_aq of S₂.

EXPERIENCES

The Salinities causing the Phase Inversion (SPI) of the reference system mixed with 12 ionic and 10 nonionic well-defined surfactants are determined in order to quantify the contributions of the nature of the polar head and of the alkyl chain length.

FINDINGS

The SPI varies linearly upon the addition of S₂. The slope of the straight variation with the molar fraction of S₂ is called the "SPI-slope". It quantifies the hydrophilic/lipophilic ratio of S₂ in saline environment and its salt-sensitivity with respect to the reference surfactant C₁₀E₄. The SPI-slopes of C₁₂ surfactants bearing different polar heads are found to decrease in the following order: C₁₂NMe₃Br > C₁₂E₈ > C₁₂E₇ ≥C₁₂SO₃Na ≈ C₁₂COONa ≥ C₁₂SO₄Na > C₁₂E₆ > C₁₂E₅ > C₁₂E₃. This classification is different from that obtained when the phase inversion is caused by a change in temperature (PIT-slope method) because the addition of NaCl in significant amounts (3 to 10 wt%) partially screens the ionic heads and diminishes their apparent hydrophilicities. A simple model, valid for all types of nonionic surfactants, is developed on the basis of the HLD_N equation (Normalized Hydrophilic-Lipophilic Deviation) to express the SPI-slope as a function of the hydrophilic/lipophilic ratio (PACN₂) and the salinity coefficient (δ₂) of S₂. All studied surfactants are positioned on a 2D map according to the values of their SPI-slope and their PIT-slope to graphically highlight their hydrophilic/lipophilic ratio and their salt-sensitivity. Finally, a linear model connecting the PIT-slope and the SPI-slope is derived for nonionics, emphasizing that the thermal partitioning of C₁₀E₄ towards n-octane is much greater in the PIT-slope than in the SPI-slope experiments.

How to Use the Normalized Hydrophilic-Lipophilic Deviation (HLDN) Concept for the Formulation of Equilibrated and Emulsified Surfactant-Oil-Water Systems for Cosmetics and Pharmaceutical Products

The effects of surfactant molecules involved in macro-, mini-, nano-, and microemulsions used in cosmetics and pharmaceuticals are related to their amphiphilic interactions with oil and water phases. Basic ideas on their behavior when they are put together in a system have resulted in the energy balance concept labeled the hydrophilic-lipophilic deviation (HLD) from optimum formulation. This semiempirical equation integrates in a simple linear relationship the effects of six to eight variables including surfactant head and tail, sometimes a cosurfactant, oil-phase nature, aqueous-phase salinity, temperature, and pressure. This is undoubtedly much more efficient than the hydrophilic-lipophilic balance (HLB) which has been used since 1950. The new HLD is quite important because it allows researchers to model and somehow predict the phase behavior, the interfacial tension between oil and water phases, their solubilization in single-phase microemulsion, as well as the corresponding properties for various kinds of macroemulsions. However, the HLD correlation, which has been developed and used in petroleum applications, is sometimes difficult to apply accurately in real cases involving ionic–nonionic surfactant mixtures and natural polar oils, as it is the case in cosmetics and pharmaceuticals. This review shows the confusion resulting from the multiple definitions of HLD and of the surfactant parameter, and proposes a “normalized” Hydrophilic-Lipophilic Deviation (HLDN) equation with a surfactant contribution parameter (SCP), to handle more exactly the effects of formulation variables on the phase behavior and the micro/macroemulsion properties.

Use of the normalized hydrophilic-lipophilic-deviation (HLDN) equation for determining the equivalent alkane carbon number (EACN) of oils and the preferred alkane carbon number (PACN) of nonionic surfactants by the fish-tail method (FTM)

The standard HLD (Hydrophilic-Lipophilic-Deviation) equation expressing quantitatively the deviation from the "optimum formulation" of Surfactant/Oil/Water systems is normalized and simplified into a relation including only the three more meaningful formulation variables, namely (i) the "Preferred Alkane Carbon Number" PACN which expresses the amphiphilicity of the surfactant, (ii) the "Equivalent Alkane Carbon Number" EACN which accurately reflects the hydrophobicity of the oil and (iii) the temperature which has a strong influence on ethoxylated surfactants and is thus selected as an effective, continuous and reversible scanning variable. The PACN and EACN values, as well as the "temperature-sensitivity-coefficient"τ of surfactants are determined by reviewing available data in the literature for 17 nonionic n-alkyl polyglycol ether (C_iE_j) surfactants and 125 well-defined oils. The key information used is the so-called "fish-tail-temperature" T* which is a unique data point in true ternary C_iE_j/Oil/Water fish diagrams. The PACNs of C_iE_j surfactants are compared with other descriptors of their amphiphilicity, namely, the cloud point, the HLB number and the PIT-slope value. The EACNs of oils are rationalized by the Effective-Packing-Parameter concept and modelled thanks to the COSMO-RS theory.

How to Attain an Ultralow Interfacial Tension and a Three-Phase Behavior with a Surfactant Formulation for Enhanced Oil Recovery: A Review. Part 2. Performance Improvement Trends from Winsor's Premise to Currently Proposed Inter- and Intra-Molecular Mixtures

The minimum interfacial tension occurrence along a formulation scan at the so-called optimum formulation is discussed to be related to the interfacial curvature. The attained minimum tension is inversely proportional to the domain size of the bicontinuous microemulsion and to the interfacial layer rigidity, but no accurate prediction is available. The data from a very simple ternary system made of pure products accurately follows the correlation for optimum formulation, and exhibit a linear relationship between the performance index as the logarithm of the minimum tension at optimum, and the formulation variables. This relation is probably too simple when the number of variables is increased as in practical cases. The review of published data for more realistic systems proposed for enhanced oil recovery over the past 30 years indicates a general guidelines following Winsor's basic studies concerning the surfactant-oil-water interfacial interactions. It is well known that the major performance benefits are achieved by blending amphiphilic species at the interface as intermolecular or intramolecular mixtures, sometimes in extremely complex formulations. The complexity is such that a good knowledge of the possible trends and an experienced practical know-how to avoid trial and error are important for the practitioner in enhanced oil recovery.