Surface Properties of Glucose-Based Surfactants and Their Application in Textile Dyeing with Natural Dyes

In this study, propylene glycol-based glycosides were obtained using an acetalization reaction in which glucose was first reacted with propylene glycol. Subsequently, the propylene glycol glycoside was reacted with alkyl glycidyl ether of varying carbon chain lengths (i.e., 08-G, 10-G, 12-G, 14-G, and 16-G) to synthesize a series of glucose-based biodegradable surfactants. The experimental results show that the surface activity of the C₈–C₁₂ glucose-based surfactants increases with the carbon chain length. However, the surface activity of the C₁₄–C₁₆ glucose-based surfactants decreased as the carbon chain length increased. Among all the surfactants, the C₁₂ glucose-based surfactant exhibited the most efficient emulsification ability, lowest surface tension, lowest fluorescence intensity, highest zeta potential, and good emulsification stability. The glucose-based surfactants were used as additives in natural plant dyes made from turmeric or henna to dye wool fabrics. Higher color strengths were observed in the C₁₄ glucose-based surfactant.     

Effects of Surfactant Headgroups on Oil-in-Water Emulsion Droplet Formation: An Experimental and Simulation Study

Nonpolar oils such as kerosene and diesel oil are common collectors in coal flotation. Surfactants are usually added to the pulp to emulsify the oil collectors. The present study used dodecane as the oil collector and anionic sodium dodecyl sulfonate (SDS) and nonionic tetraethylene glycol monododecyl ether (C₁₂EO) with different headgroups and identical chain alkyls to investigate the effect of the surfactant headgroups on oil-in-water emulsion droplet formation. The morphology and stability of dodecane emulsions were determined experimentally. Density functional theory (DFT) and molecular dynamics (MD) simulations were used to explain the microscopic mechanism. The results of DFT indicated a larger interaction between SDS and the water molecules than that between C₁₂EO and water molecules. The results obtained by MD suggested that the SDS headgroup exhibited a loose arrangement and a relatively large gap size, thereby weakening the interaction between SDS and water molecules at the dodecane/water interface. In contrast, the headgroups of C₁₂EO were bent and interwoven with others to form a tight reticulation at the interface. According to the simulation results, the ability of the surfactant to form dodecane-in-water emulsion droplets depends on the arrangement of the surfactants at the oil–water interface rather than on the interaction strength between the headgroups of the surfactants and water molecules. The presented microscopic mechanism of the surfactant headgroup formation of oil-in-water emulsion droplets offers surfactant selection and design references.     

Synthesis, Surface and Thermodynamic Properties of Substituted Polytriethanolamine Nonionic Surfactants

Three series of nonionic surfactants derived from polytriethanolamine containing 8, 10, and 12 units of triethanolamine were synthesized. Structural assignment of the different compounds was made on the basis of FTIR and ¹H‐NMR spectroscopic data. The surface parameters of these surfactants included critical micelle concentration (CMC), surface tension at the CMC (γ_CMC), surfactant concentration required to reduce the surface tension of the solvent by 20 mN m^?1 (pC₂₀), maximum surface excess (Γ_max), and the interfacial area occupied by the surfactant molecules (A_min) using surface tension measurements. The micellization and adsorption free energies were calculated at 25 °C.     

Surface activity of mixtures of narrow-range distributed alcohol oxyethylates and sodium dodecylbenzenesulfonate

Surface and interfacial tension, emulsion inversion temperature, and detergency were determined for mixtures of sodium dodecylbenzenesulfonate and narrow-range distributed alcohol C₁₂−C₁₄ oxyethylates of different hydrophilicity. The mixtures of ionic and nonionic surfactants behave similarly to nonionic and ionic surfactants at the air/water and hydrocarbon/water interfaces, respectively. The air/water interface is mainly occupied by nonionic surfactant molecules. However, the interfacial tensions for mixtures of nonionic and ionic surfactants are similar to those of sodium dodecylbenzenesulfonate. Mixtures of narrow-range distributed oxyethylates and sodium dodecylbenzenesulfonate have a higher detergency at 40°C than individual components.     

Synthesis and Evaluation of Novel Amido-Amine Cationic Gemini Surfactants Containing Flexible and Rigid Spacers

New amido‐amine‐based cationic gemini surfactants with flexible and rigid spacers and different hydrophobic tails were synthesized and characterized. These gemini surfactants were prepared by a modified procedure through amidation of long chain carboxylic acids using 3‐(dimethylamino)‐1‐propylamine followed by treatment with halohydrocarbons. The effect of the trans and cis conformation of the spacer double bond was investigated by means of critical micelle concentration, surface tension reduction, and thermal stability. The short‐term thermal stability of the gemini surfactants was assessed using thermogravimetric analysis (TGA) and the long‐term thermal stability was examined by a unique approach based on structure characterization techniques including NMR (¹H and ¹³C) and FTIR analysis. TGA results demonstrated excellent short‐term thermal stability since no structure degradation was observed up to 200 °C. Structural characterization revealed impressive long‐term thermal stability of the gemini surfactants with no structure decomposition after exposing them to 90 °C for 10 days. The critical micelle concentration of gemini surfactants was found to be in the range of 0.77 × 10^?4–3.61 × 10^?4 mol L^?1 and corresponding surface tension (γ_CMC) ranged from 30.34 to 38.12 mN m^?1. The surfactant with the trans conformation of spacer double bond showed better surface properties compared to the surfactant with the cis conformation of spacer double bond. Similarly, increasing surfactant tail length and spacer length resulted in decreasing CMC values. Moreover, bromide counterion showed improved surface properties compared to chloride counterion.     

Synergistic Behavior of a Triblock Copolymer with Anionic and Cationic Surfactants in Aqueous Solution

The synergistic behavior of poly(ethylene oxide)–poly(propylene oxide)–poly(ethylene oxide) (PEO–PPO–PEO) triblock copolymer in aqueous solution with the synthesized anionic surfactants [decyl sulfonate (A10), myristyl sulfonate (A14) and cetyl sulfonate (A16)] and cationic surfactants [decyl pyridinium bromide (C10), myristyl peridinium bromide (C14) and cetyl pyridinium bromide (C16)] was investigated using a surface tension technique at 25 °C. The results show that the CMC values of binary mixtures for anionic and cationic surfactants with the triblock copolymer are lower than that of single surfactants. The synergistic interaction between surfactant molecules and copolymer molecules in binary mixed solution enhance the adsorption of surfactant molecules at the interface. The micellar mole fractions (X _m) and the interaction parameter (β) of these surfactants in mixed micelles were determined.

Effect of surfactant in a modified sol on the physicochemical properties and photocatalytic activity of crystalline TiO<Subscript>2</Subscript> nanoparticles

This study describes the effect of amphiphilic organic molecules (surfactants) in a sol on the physicochemical properties and photocatalytic activity of crystalline TiO₂ nanoparticles prepared via a simple sol–gel route at high temperatures from 400 to 800 °C. Addition of polyoxyethylenesorbitan surfactant and polyethylene oxide and polypropylene oxide triblock copolymer as particle size inhibitors and pore directing agents into a stable titania sol affected the physicochemical properties of TiO₂ nanoparticles such as their crystallographic structure, morphology, and defect structure. With the addition of the surfactants, the ratio of anatase and rutile crystal phases of TiO₂ was controlled and an active anatase crystal phase was maintained during heat treatment up to 800 °C. Decrease in the sintering rate and inhibition in crystal growth were also observed, which resulted in higher surface area and inhibition of crystallite aggregation. Bulk defects in TiO₂ were reduced while surface defects were increased as a result of the addition of surfactants. These physicochemical properties of TiO₂ nanoparticles were correlated with photocatalytic degradation of 4-chlorophenol in water. The results revealed that high crystallinity, anatase crystal phase, high specific surface area, surface defects, and segregated morphology of TiO₂ nanoparticles, which were induced by the addition of surfactants, were more advantageous for enhancing photocatalytic destruction of the model organic compound tested in the study.     

Cold Water Detergency of Triacylglycerol Semisolid Soils: The Effect of Salinity,Alcohol Type,and Surfactant Systems

Cold water detergency of triacylglycerol semisolid soils is much more challenging than liquid vegetable oils due to poorer interaction between surfactants and semisolid soil. This research seeks to improve the removal efficiency of semisolid soils below their melting points using surfactant-based formulations containing different alcohol additives. To this end, cold water detergency of solid coconut oil and solid palm kernel oil was investigated in various surfactant/alcohol systems, including single anionic extended surfactants, single nonionic alcohol ethoxylate surfactants, and a mixture of anionic surfactants. A series of alcohols (2-butanol, 1-hexanol, 1-heptanol, 1-octanol, 1-nonanol, and 1-decanol) were added to the surfactant formulations to investigate cold water detergency improvement. While cold water detergency using surfactants alone was poor, it was considerably improved when optimum salinity (S*) and 1-heptanol, 1-octanol, or 1-nonanol were introduced to the studied surfactant formulations. The maximum detergency of solid coconut oil exceeded 90% removal in the 0.1 w/v% C_14-15-8PO-SO₄Na/0.2 w/v% 1-octanol/4 w/v% NaCl system (a final optimized surfactant system) at a washing temperature of 10°C versus 22.9 ± 2.2% in the surfactant alone (not at optimum salinity and no additive). Further analysis showed that improved cold water detergency using surfactant/intermediate-chain alcohols/NaCl could be correlated with high wettability (low contact angle) as well as favorable surfactant system-soil interaction as observed by lower interfacial tension values. In contrast, the improved cold water detergency was observed to be independent of dispersion stability. This work thus demonstrates that surfactant system design, including additives, can improve cold water detergency of semisolid soils and should be further explored in future research.     

Dynamic surface tension of aqueous surfactant solutions. 6. Compounds containing two hydrophilic head groups and two or three hydrophobic groups and their mixtures with other surfactants

Dynamic surface tensions (γ_t)—measured by the maximum bubble pressure method—of some surfactants containing two hydrophilic (sulfonate) groups and two or three hydrophobic groups in the molecule (“gemini surfactants”), and of their mixtures with a nonionic surfactant or an amine oxide, have been measured at 25°C in 0.1 M NaCl. Linearity of the plots of surface pressure vs. square root of the surface age indicated that the systems studied were all diffusion-controlled. For the individual surfactant systems, the apparent diffusion coefficient decreases with an increase in the number of alkyl chains and the bulkiness of the surfactant molecules. For the mixtures, when interaction between the two surfactants is weak, γ_t at short times (t<1s) is close to that of the component with the lower surface tension; at longer times, it is closer to that of the component with the lower equilibrium surface tension. When interaction is strong, γ_t at short times is greater than that of either component. The molar ratio at which maximum effect on γ_t is observed depends upon the strength of the interactions between the two surfactants.     

Mixed Micellar Properties and Related Interaction Parameters of Butanediyl-1,4-bis(dodecyl dimethyl ammonium bromide) Gemini Surfactant with Nonionic Amphiphiles

Mixed micellization of cationic gemini surfactant butanediyl-1,4-bis(dimethyldodecylammonium bromide) with nonionic surfactants (sorbitan esters, alcohols and phenol ethoxylates) and triblock copolymers has been studied tensiometrically. Various physicochemical parameters of the studied systems including ideal CMC values, experimental and ideal micellar compositions, interaction parameters, activity coefficients of the components, etc. have been evaluated by considering theoretical models of Clint, Rubingh, Rosen and Maeda. The experimental critical micelle concentration (CMC) values of the mixed micelles were lower than the CMC values of the individual components and showed a negative deviation from ideal CMC (CMC*) values. The analysis reveals that the mole fractions of gemini are lower compared to the nonionic surfactants/triblock polymers and the values of ΔG _m ^° , ΔG _ad ^° , G _min and ΔG _ex ^m show that the spontaneity of the studied mixed micelles relatively decreases as the content of the gemini in the bulk phase increases.     

A Systematic Study of Mixed Surfactant Solutions of a Cationic Ester-Bonded Dimeric Surfactant with Cationic, Anionic and Nonionic Monomeric Surfactants in Aqueous Media

A novel cationic biodegradable dimeric (gemini) surfactant, ethane-1,2-diyl bis(N,N-dimethyl-N-hexadecylammoniumacetoxy) dichloride (16-E2-16), containing an ester-linked spacer was synthesized. Its pure and mixed micellization properties with monomeric surfactants cetyl trimethyl ammonium chloride, cetyl pyridinium chloride, sodium dodecyl sulfate, sodium dodecyl benzene sulfonate, cetyl alcohol ethoxylate (20EO) and tert-octylphenol ethoxylate (9.5EO) were investigated by surface tension measurements at 30 °C. The critical micelle concentration (CMC) of 16-E2-16 is well below that of cetyl trimethyl ammonium chloride containing the same number of carbon atoms in the hydrophobic tail per polar head. At different mole fractions of the gemini surfactant, the CMCs of the gemini-conventional binary mixtures were determined and were found to be less than the ideal CMC values in all the cases indicating synergistic interactions. Aggregation number and Stern–Volmer constant, obtained by the fluorescence quenching technique, also support the synergistic behavior of the surfactant systems.     

Optimized Microemulsion Systems for Detergency of Vegetable Oils at Low Surfactant Concentration and Bath Temperature

Triglycerides and vegetable oils are amongst the most difficult oils to remove from fabrics due to their highly hydrophobic nature; this is all the more challenging as cold water detergency is pursued in the interest of energy efficiency. Recently, extended surfactants have produced very encouraging detergency performance at ambient temperature, especially at low surfactant concentration. However, the salinity requirement for extended surfactants was excessive (4–14%) and there is limited research on extended‐surfactant‐based microemulsions for cold water detergency (below 25 °C). Therefore, extended‐surfactant‐based microemulsions are introduced in this study for cold temperature detergency of vegetable oils with promising salinity and surfactant concentration. The overall goal of this study is to explore the optimized microemulsion formulations with low surfactant and salt concentration using extended surfactant for canola oil detergency at both 25 and 10 °C. It was found that microemulsion systems achieved good performances (higher than those of commercial detergents) corresponding to IFT value 0.1–1 mN/m with the surfactant concentration as low as 10 ppm and 4% NaCl at 25 °C, and as low as 250 ppm and 0.1% (1000 ppm) NaCl at 10 °C. In addition, microemulsion systems were investigated with a different salt (CaCl₂, or water hardness, versus NaCl) at 10 °C, demonstrating that 0.025% CaCl₂ (250 ppm) can produce good detergency; this is in the hardness range of natural water. These results provide qualitative guidance for microemulsion formulations of vegetable oil detergency and for future design of energy‐efficient microemulsion systems.     

Synthesis,Characterization and Surface Properties of Amidosulfobetaine Surfactants Bearing Odd-Number Hydrophobic Tail

Three amidosulfobetaine surfactants were synthesized namely: 3-(N-pentadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2a); 3-(N-heptadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2b), and 3-(N-nonadecanamidopropyl-N,N-dimethyl ammonium) propanesulfonate (2c). These surfactants were prepared by direct amidation of commercially available fatty acids with 3-(dimethylamino)-1-propylamine and subsequent reaction with 1,3-propanesultone to obtain quaternary ammonium salts. The synthesized surfactants were characterized by IR, NMR and mass spectrometry. Thermogravimetric analysis (TGA) results showed that the synthesized surfactants have excellent thermal stability with no major thermal degradation below 300 °C. The critical micelle concentration (CMC) values of the surfactants 2a and 2b were found to be 2.2 × 10^?4 and 1.04 × 10^?4 mol/L, and the corresponding surface tension (γ_CMC) values were 33.14 and 34.89 mN m^?1, respectively. The surfactants exhibit excellent surface properties, which are comparable with conventional surfactants. The intrinsic viscosity of surfactant (2b) was studied at various temperatures and concentrations of multi-component brine solution. The plot of natural logarithm of relative viscosity versus surfactant concentration obtained from Higiro et al. model best fit the surfactant behavior. Due to good salt resistance, excellent surface properties and thermal stability, the synthesized surfactant has potential to be used in various oil field applications such as enhanced oil recovery, fracturing, acid diversion, and well stimulation.     

Comparison of QSAR and QSPR Based Aquatic Toxicity for Mixed Surfactants

In the present study, quantitative structure-activity relationship (QSAR) equations were derived using the logarithm of the octanol/water partition co-efficient for the prediction of acute aquatic toxicity of mixed surfactant systems. Further mixed surfactant systems of an anionic surfactant (sodium lauryl sulfate) and several nonionic surfactants (alkyl polyglucoside) of different hydrophobic chain lengths were taken together to calculate the parameter pEC50. Quantitative structure-properties relationship (QSPR) equations based on pC20, and A _min were developed from the surface tension data to predict pEC50 values and compared with QSAR derived pEC50 values to understand the probable mechanisms of action of the mixed surfactants blends for aquatic toxicity. The established QSAR and QSPR equations for mixed surfactants indicate that given blends of surfactants act as a polar narcotic.

Synthesis,Micellization, and Surface Activity of Novel Linear-Dendritic Carboxylate Surfactants

Two generations of novel linear-dendritic carboxylate surfactants C₁₈-G₁-(COONa)₂ and C₁₈-G₂-(COONa)₄ have been synthesized by the divergent method and their structures are characterized by ¹H Nuclear Magnetic Resonance and Infrared analysis. The electrical conductivity measurement is used to measure the Krafft temperatures of C₁₈-G₁-(COONa)₂ and C₁₈-G₂-(COONa)₄, which are much smaller than those of the corresponding conventional surfactant sodium stearate. The markedly enhanced solubility of two linear-dendritic surfactants is ascribed to the high hydrophilicity of surfactant headgroups induced by the carboxylate and ester groups. The critical micelle concentration (CMC) values obtained from both the electrical conductivity and surface tension measurements indicate that the micellizations of linear-dendritic surfactants become favorable with the increase in the number of the surfactant headgroup. However, the surface activity parameters including the surface tension at the CMC, maximum surface excess, and minimum surface area reveal that C₁₈-G₁-(COONa)₂ exhibits greater efficiency in absorbing at the air/water interface compared to C₁₈-G₂-(COONa)₄, owing to their different steric repulsions of the surfactant headgroups. In addition, C₁₈-G₁-(COONa)₂ and C₁₈-G₂-(COONa)₄ have higher emulsifying ability than the conventional surfactants sodium stearate and sodium octadecyl sulfate.     

Synthesis and Study of the Surface Properties of Alkylnaphthalene and Alkylphenanthrene Sulfonates

Some alkylnaphthalene and alkylphenanthrene sulfonates were synthesized by means of a Wurtz–Fittig reaction. The HLB values for the prepared compounds were calculated, and the basic properties were studied in water at different temperatures, namely, 25, 35 and 45 °C. Through surface tension measurements, the following values were determined: the critical micelle concentration (CMC) and the surface tension at the CMC (γ_CMC). The following values were calculated: area per molecule at the CMC (A_CMC), standard free energy change of micellization (ΔG _mic), standard free energy of adsorption (ΔG _ad), and the efficiency of a surfactant in reducing surface tension (pC20). Furthermore, the partition coefficients of the synthesized compounds were also measured. The results show that n-alkylnaphthalene and n-alkylphenanthrene surfactants studied exhibit desirable properties that may be of value in some fields such as detergency. To confirm the detergency power of the prepared surfactants, some foam studies were performed.     

Environmental Impact of Ether Carboxylic Derivative Surfactants

The ultimate aerobic biodegradability and toxicity of three ether carboxylic derivative surfactants having different alkyl chains and degrees of ethoxylation were investigated. Ultimate aerobic biodegradability was screened by means of dissolved organic carbon determinations at different initial surfactant concentrations. For comparison, the characteristic parameters of the biodegradation process, such as half-life, mean biodegradation rate, and residual surfactant concentration, were determined. Increased surfactant concentrations decreased mineralization and lengthened the estimated half-life. The results demonstrate that the ultimate aerobic biodegradability is higher for the surfactants with the shortest alkyl chain and highest degree of ethoxylation. Toxicity values of the surfactants, and their binary mixtures, were determined using three test organisms, the freshwater crustacea Daphnia magna, the luminescent bacterium Vibrio fischeri and the microalgae Selenastrum capricornutum. The toxicity is lower for the surfactants with the shortest alkyl chain and highest degree of ethoxylation. The toxicity of binary mixtures of the three ether carboxylate surfactants at a 1:1 weight ratio was also measured. The least toxic mixture is formed by the surfactants having lower individual toxicity.     

The physicochemical and fire extinguishing performance of aqueous film-forming foams based on a class of short-chain fluorinated surfactants

Aqueous film-forming foams (AFFFs) are an important for fire extinguishing, and their key ingredient is fluorinated surfactant. In recent years, traditional long-chain fluorinated surfactants have been banned by most countries because of their persistence, bio-accumulation and toxicity. Therefore, increased attention has been paid to the research and development of short-chain fluorinated surfactants. As is well known, the introduction of hydrophilic or hydrophobic groups in a surfactant affects its surface activity, and therefore, the fire extinguishing performance of AFFFs. In this work, a series of short-chain fluorosurfactant-based AFFFs with different hydrophobic chain lengths were prepared. The physicochemical performance of mixed systems (fluorinated surfactant plus sodium hexanesulfonate), including surface activity, spreading ability, foam expansion, drainage time, and the fire extinguishing and burn-back performance of AFFFs were studied. The results show that the critical micelle concentration (CMC) and the surface tension (γ_CMC) at the CMC of mixed systems at 25°C are lower than 7.68 mmol/L and 16.51 mN/m, respectively. For mixed systems, the average spreading rate is more than 1.09 cm/s, the foam expansion is over 7.1, and the drainage time is greater than 3.28 min. The fire extinguishing time of AFFFs on fuels is less than 51 s while the burn-back time is more than 15.18 min. The results imply a potential application prospect of the short-chain fluorinated surfactants in AFFFs.     

Wetting of hydrophobic substrates by nanodroplets of aqueous trisiloxane and alkyl polyethoxylate surfactant solutions

Trisiloxane surfactants at low concentrations promote the complete and rapid wetting of aqueous droplets on very hydrophobic (hydrocarbon) substrates. This behavior has not been demonstrated by any other surfactant which explains why the trisiloxanes are referred to as superspreaders. Despite many experimental and theoretical investigations the mechanism of superspreading is not fully understood. Molecular dynamics simulations using all-atom force fields have been conducted to attempt to elucidate the mechanism of superspreading. Spherical nanodroplets containing approximately 10,000 water molecules in the bulk and 475 surfactant molecules at the liquid-vapor interface were placed in the vicinity of a graphite substrate and allowed to spread freely at room temperature. In the trisiloxane case the droplet was found to spread very little, although randomly removing 175 surfactant molecules lowered the final contact angle from 110^° to 80^°. In contrast, an alkyl polyethoxylate surfactant-laden droplet was found to spread significantly further, with the equilibrium contact angle reaching 55^°. Similar results for the two surfactant systems were found for cylindrical nanodroplets spreading on a self-assembled monolayer (SAM). The reasons for the lack of spreading in the trisiloxane case and the simulation challenges associated with these systems are discussed. In support of our arguments we demonstrate that the surfactant molecules of an initially uniform aqueous trisiloxane solution self-assemble into a bilayer in tens of nanoseconds on a graphite substrate. Lastly, in a final set of simulations, neat trisiloxane droplets at 450 K are found to arrange into a layered structure on a methyl-terminated SAM and to form a sand pile-shape on a hydroxyl-terminated SAM.     

Self-Assembly of Polyethylene Glycol Ether Surfactants in Aqueous Solutions: The Effect of Linker between Alkyl and Ethoxylate

The aqueous self-assembly behavior of two homologous series of poly(ethylene oxide) (PEO)-containing nonionic surfactants based on a C₁₀-Guerbet hydrophobe is reported. The two families of surfactants, alkyl ethoxylates and alkyl alkoxylates, are commercially available from BASF under the trade name Lutensol® XP-series and XL-series, respectively. The latter incorporate propylene oxide (PO) units in the surfactant chain. Dye solubilization was used to determine the critical micellization concentration (CMC) of each surfactant at 22 and 50 °C. The PO-containing alkyl alkoxylates displayed lower CMC values, which were also more sensitive to temperature. The Gibbs free energy, enthalpy, and entropy of micellization were computed from the CMC data and used to identify the contribution of each surfactant moiety (alkyl chain, PO unit, and PEO block) in controlling the CMC. The micellization properties are compared with compositionally similar surfactants with linear alkyl chains, yielding information about the effects of the Guerbet alkyl chain on micellization. Isothermal titration calorimetry was also used to characterize the CMC and enthalpy of micellization which generally compare well with the dye solubilization results. Cloud point data reveal nonmonotonic relationships for the Lutensol® surfactants with respect to composition, unlike linear alkyl chain surfactants. Finally, dilute solution viscosity measurements performed on some Lutensol® surfactants show a change in the slope, suggesting a structural change that tends to be more pronounced for surfactants with longer PEO blocks. The data presented herein enhance the understanding of surfactant structure–property relationships required for industrial formulation.