Homologous Series Of Nonionic Surfactants Research Articles

An empirical model to represent the CMC behavior of aqueous solutions of homologous series of nonionic surfactants, related to its chemical constitution

• The Critical Micelle Concentration (CMC) is a fundamental property of surfactants. • An empirical model is presented based on the thermodynamics of micellization of a given homologous series of surfactants. • The reason for the observed increase and decrease in CMC value is explained. • The proposed model is compared with other empirical models and its quality to estimate the CMC is superior. Critical Micelle Concentration (CMC) is a fundamental property of surfactants in (aqueous) solution. The importance of defining the CMC of an aqueous surfactant solution is related to the different behavior and performance of the given system below and above its CMC, which has impact on the usage of this type of systems for different industrial applications. In this work, an empirical model is presented, based on the fundamental equation for the thermodynamics of micellization of a given homologous series of surfactants with the same chemical nature, to estimate the corresponding CMC. This simple model contains three adjustable parameters and allows predicting the log[CMC] of the nonionic surfactants polyoxyethylene alkyl ethers (C n E m ) in aqueous solution. The analysis of the three parameters showed that the hydrophobic characteristics play the major role in micelle formation. The polarity of the molecules is also important, but its effect is less pronounced. The proposed model is compared with other empirical models and its quality to estimate the CMC is superior.

Molecular Design and Structure-Property Investigation of n-Dodecylbenzyloxy Ethoxylates.

Nonylphenol ethoxylates (NPEOn) exhibit outstanding application performances, especially in stabilizing silicone oil emulsions, but have been globally banned or use-restricted for serious ecological toxicity. A homologous series of nonionic surfactants, n-dodecylbenzyloxy ethoxylates (DBEOn), are molecularly designed and synthesized as alternatives to NPEOn, where the phenolic group of NPEOn was replaced by a benzyloxy group to counteract the harmful characteristics of NPEOn, while retaining the benefits. Based on computational studies, we propose a hypothesis that has a conjugation reduction effect (CRE) of DBEOn relative to NPEOn on the surfactant structure and properties that solves the biodegradation problem while maintaining the outstanding emulsifying capacity of NPEOn. A 7-day activated sludge assessment shows that DBEO8, a representative member of DBEOn, is almost 100% biodegradable and that the poor biodegradability of NPEOn may be improved by maintaining the vital benzene ring in DBEOn molecules, because the oxygen atom of the benzyloxy group is separated from the smaller conjugation system of DBEOn. Compared to NPEO10, DBEO8 has a similar cloud point but exhibits higher benzene solubilization and considerably higher emulsion stabilities for mineral oil, biomass oil, and especially silicone oil; this outcome is ascribed to a probable random coil configuration of PEO caused by the CRE of DBEOn. Therefore, molecular design produces DBEOn with both excellent biodegradability and outstanding application performances, especially in terms of excellent emulsion stabilities of various oils, as predicted by the CRE hypothesis, thereby serving as an effective alternative to NPEOn.

Theoretical description of 2D-cluster formation of nonionic surfactants at the air/water interface

Recent progress in modeling of the surfactant behavior from atomistic to continuous at the air/water interface across different space-time scales is reviewed. Advantages and disadvantages of modern quantum mechanical, molecular dynamical, and mesoscale methods are discussed for description of interactions between amphiphilic molecules leading to formation of 2D films. The use of nonempirical and semiempirical methods for assessment of the thermodynamic and structural parameters of large van der Waals complexes is of particular interest. An approach for calculation of the thermodynamic and structural parameters of clusterization for nonionic surfactants at the air/water interface is proposed on the basis of the quantum chemical semiempirical PM3 method. This approach implicitly takes into account the influence of the interface on the surfactant molecules via stretching and orienting effect. The calculations are carried out in the supermolecule approximation for a limited number of small amphiphilic aggregates with different alkyl chain. The correlation analysis of the calculated data array provides the increments contributing by the intermolecular CH · · · HC interactions and interactions between hydrophilic parts into the thermodynamic parameters of formation and clusterization. Obtained increments are further used for constructing the dependencies of the thermodynamic clusterization parameters per one monomer on the alkyl chain length for large clusters up to 2D films. In the framework of the proposed theoretical approach, the next parameters are calculated as follows: enthalpy, entropy, and Gibbs’ energy of clusterization for 11 homologous series of nonionic surfactants, threshold chain length enabling the process of monolayer formation at standard conditions, the “temperature effect” of clusterization, and the structural parameters of the monolayer unit cell (particularly the tilt angle) depending on the size of the hydrophilic headgroup of the amphiphilic compound.

Interaction behavior in ultrafiltration of nonionic surfactant micelles by adsorption

Adsorption of nonionic surfactant micelles onto ultrafiltration (UF), membranes was studied. Two homologous series of nonionic surfactants, namely, Tritons (alkylphenol ethoxylates) and Neodols (alcohol ethoxylates), were used to characterize surface properties of two polymeric ultrafiltration membranes with 20,000 nominal cutoff. Particularly, a cellulose acetate and a polysulfone membrane were investigated. Static adsorption experiments were carried out using surfactant solutions at concentrations above their critical micelle concentration. The characterization of surface properties of UF membranes was based on the adsorption behavior of surfactant species. The adsorption extent on UF membranes was affected by the hydrophobicity-to-hydrophilicity ratio mainly determining the interactions developed at the membrane–surfactant species interface. Adsorption experimental data seem generally to fit the Langmuir isotherm model. Atomic force microscopy was used to examine the alteration of the top membrane surface morphology.

Hydration pressure of a homologous series of nonionic alkyl hydroxyoligo(ethylene oxide) surfactants

The hydration pressure of a homologous series of nonionic surfactants of the type CH3(CH2)n−1(OCH2CH2)mOH (CnEm) was determined by using sorption gravimetry. The hydration pressure shows a non-exponential decay on hydration and the curves are best fitted with a rational function. The non-exponential character is explained by contributions arising from the bending energy of non-lamellar liquid crystalline phases. The parameters obtained show that hydration of pure nonionic surfactants is correlated with the number of the oxyethylene groups in the headgroup. However, they are almost independent of the length of the alkyl chain. Exceptions are surfactants in the solid crystalline state that almost prevent hydration. Furthermore, the respective mesophase structures do not dominate the hydration behaviour. The Gibbs free energy (free enthalpy) of hydration is −1.1 kJ mol−1 per oxyethylene group.

Effect of inorganic additives on solutions of nonionic surfactants — XVI. Limiting cloud points of highly polyoxyethylated surfactants

As their degree of polyoxyethylation is increased, the cloud points (CPs) of three homologous series of nonionic surfactants (NSs) rise steeply at first but then level off, converging asymptotically to the temperature range of 114–118°C, which corresponds to the CP of polyethylene oxide with a molecular weight of 10 4. Six of the 14 surfactants investigated were octoxynols, five were nonoxynols and three were polyoxyethylene dodecyl ethers. Ten had an average number of oxyethylene units per molecule p>20 and a CP>100°C. Three of these CPs were measured directly on 2.00% surfactant solutions sealed into ampoules. To avoid additional measurements under pressure, the other surfactants had their CPs lowered below the normal boiling point of their 2.00% solutions by adding the salting-out, CP-lowering salt NaNO 3 at various concentrations, measuring the depressed CPs and extrapolating them to zero salt concentration. The CPs decrease linearlv with increasing molality m of NaNO 3 up to ca. 2.5 m and more steeply at higher concentration. For a given concentration of NaNO 3, larger p values result in more extensive salting out: The more highly polyoxyethylated a surfactant is, the greater the reduction in CP it undergoes. As p increases, the curves of CP in water versus p for the octoxynols and nonoxynols rise steeply and nearly linearly, reaching 100 and 103°C at p=16, and then begin to level off. The sharpest inflections are at p=22–25. The nonoxynol curve becomes horizontal at p≅40 and 115°C while the octoxynol curve rises gently from 3°C below the nonoxynol curve to merge with it at p=90 and 114°C. The CPs of the three polyoxyethylene dodecyl ethers are slightly higher than those of the polyoxyethylated alkylphenols with comparable p values, peaking at 118°C. The most highly polyoxyethylated surfactant of each series contains 95% polyoxyethylene. Their CP range of 114–118°C equals that of polyethylene oxides with molecular weights between 8000 and 20 000. Published quantitative CP– p relations for polyoxyethylated NSs cover only CP values below 100°C and p values below 16. They fail to predict the levelling off of the CPs as the p values rise above 16.

Interaction behaviour in ultrafiltration of nonionic surfactants Part II. Static adsorption below CMC

Two homologous series of nonionic surfactants, namely Rhom and Haas' tritons (alkylphenol ethoxylates) and Shell dobanols (dobanol ethoxylates) were used to characterize surface properties of ultrafiltration membranes. Static adsorption experiments were carried out to reveal the interactions developed between the membrane and the nonionic surfactant. The surfactant adsorption on the membranes depends on the chemical composition and structure of both the membranes and the surfactants used, as both chemical composition and structure determine the type of interactions controlling this adsorption illustrated on the adsorption isotherms. Distinct different behaviour was exhibited by four types of membranes of the same nominal molecular weight cut-off. The influence of pH and ionic strength was studied also.

Polarographic studies of non-ionic surfactants with reference to their structural influence on surface activity

Abstract The surface activity of a homologous series of non-ionic surfactants having 12–16 carbon atoms in the alkyl chain and different lengths of the polyoxyethylene (POE) group was studied by a direct current polarographic method. Polarographic micelle points (PMPs) were used to compare the surface activities of the non-ionic surfactants in dimethylformamide (DMF) media. Results obtained from this study showed that the PMP increased regularly as the percentage of DMF in the solutions increased, indicating a decrease in the surface activity. In DMF media, as in water, the surface activity of the non-ionic surfactants depends on the hydrophilic/lipophilic ratio. Either increasing the length of the alkyl chain or decreasing the length of the polyoxyethylene chain contributes both to an enhanced hydrophobicity and an increased surface activity of the non-ionic surfactants.

Activity and stability ofPenicillium cyclopium lipase in surfactant and detergent solutions

AbstractActivity and stability of an alkaline lipase fromPenicillium cyclopium var.album (PG 37) were studied in surfactant and detergent solutions. Three anionic surfactants [Na salts of C12SO4− (sodium dodecyl sulfate), C12ØSO3/− (linear alkyl benzene sulfonate), and C11COO− (laurate)] and four homologous series of nonionic surfactants of C12–15 polyoxethylenated fatty alcohols (AEO3, AEO5, AEO7, and AEO9) were evaluated. At a concentration range of 3.2–40 μM, sodium dodecyl sulfate and laurate stimulated the activity of PG 37 lipase. At concentrations greater than 5.6 μM, linear alkylbenzene sulfonate inhibited PG 37 lipase activity. Nonionic surfactants, AEO5 and AEO7, in the concentration range of 0.25–20 mM, enhanced and stabilized the activity of PG 37 lipase. The presence of PG 37 lipase in detergent formulaton improved detergency ∼20%. The mechanism of inhibition of the lipolytic activity of PG 37 lipase is proposed to be partly due to the formation of inactive (BR)n‐E complex between the hydrophobic moiety of the surfactants and the surface of the lipase. Conversely, formation of a soluble (RB)n‐E complex between the hydrophilic group of the surfactant and lipase may account for the increased lipolytic activity of PG 37 lipase.

Synthesis and properties of some novel nonionic polyol surfactants

A homologous series of nonionic surfactants 4 based on sugar lactones has been synthesised and evaluated.

Relationship Between the Lipophilicity and Specific Hydrophobic Surface Area of Non Homologous Series of Nonionic Surfactants

AbstractThe lipophilicity (RM), specific hydrophobic surface area and the relative strength of interaction between trimethyl‐β‐cyclodextrin and 39 nonionic surfactants having different hydrophobic moieties has been determined by charge‐transfer thin‐layer chromatography using methanol as an organic modifier. RM values decreased linearly with increasing concentration of methanol. The significant correlation between the RM value extrapolated to water and the specific hydrophobic surface area indicates that these surfactants can be considered from the chromatographic point of view as a homologous series of solutes independently of their structural inhomogeneity. Stepwise regression analysis suggested that the length of alkyl chain in the hydrophobic moiety, the presence of sorbite and phenyl group in the surfactant molecule, and the number of ethyleneoxide groups per molecule have the highest impact on their hydrophobic parameters. The relative strength of surfactant‐cyclodextrin interaction significantly depended on the lipophilicity of the surfactants, and on the presence of phenyl group and ester bonds in the surfactant molecule.

Interaction of Surfactant and Leaf Surface in Glyphosate Absorption

The effect of oxyethylene (OE) chain length of three homologous series of nonionic surfactants (allinol, nonoxynol, octoxynol) on glyphosate uptake was markedly affected by the leaf surface fine-structure of sugarbeet and kohlrabi. Adaxial leaf surfaces of sugarbeet were covered with a layer of amorphous wax, whereas the adaxial surface of kohlrabi leaves was covered with fine crystalline wax. Foliar uptake of glyphosate (1 mM glyphosate, 20 mM glycine, pH 3.2) averaged 4% for sugarbeet without surfactant, but droplets were not retained by kohlrabi leaves in the absence of a surfactant. Glyphosate absorption with octoxynol (9 to 10 OE units, 0.5 g L−1) was rapid initially (0 to 2 h) and leveled off about 2 h after application in both species. Absorption by sugarbeet decreased from 12 to 3% as OE content of octoxynol was increased from 5 to 30 OE units. In contrast, surfactants of intermediate OE content (octoxynol, 16 OE units) induced the greatest uptake (17%) on kohlrabi. Leaf wetting was markedly affected by surfactant and leaf surface. As OE content of octoxynol increased from 5 to 30 OE units, droplet/leaf interface areas of 1-μl droplets decreased from 4 to 3 mm2on the adaxial leaf surface of sugarbeet and from 61 to 2 mm2on kohlrabi. Concurrently, the rate of droplet evaporation (1 μl) decreased from 1.0 to 0.7 nl s−1on sugarbeet and 4.2 to 0.5 nl s−1on kohlrabi leaves. The effect of OE content on enhancement of glyphosate uptake and wetting characteristics of spray solutions was similar within species for different hydrophobic moieties but differed markedly between species.

Surface Energies of Nonionic Surfactants Adsorbed onto Nylon Fiber and a Correlation with Their Solubility Parameters

The surface energies of spin finishes adsorbed onto synthetic fibers are a major factor in determining the processing capabilities of these fibers. They also play a key role in determining how wettable the fibers are by other materials that may be applied to yarn or fabrics in later stages of processing, such as dyes, sizes, or anti-soiling agents. We have applied several homologous series of nonionic surfactants, which can be used as spin finish emulsifiers, to nylon 66 fibers and determined the polar, dispersion, and total surface energies of these adsorbed materials. We also propose a relationship between the measured surface energies and the calculated Hansen fractional solubility parameters.

Interaction behaviour in ultrafiltration of nonionic surfactants. Part 1. Flux behaviour

Two homologous series of nonionic surfactants, namely Rohm and Haas' tritons (alkylphenol ethoxylates) and Shell's dobanols (dobanol ethoxylates), were used in order to characterize surface properties of ultrafiltration membranes. The effects of surfactant molecule hydrophilicity (characterized by the number of contained ethoxy groups) as well as of the variation of surfactant concentration and trans-membrane pressure on the permeate flux were studied. Distinctly different behaviours were shown by a polysulphone and a cellulose acetate membrane of the same nominal molecular weight cut-off. On a qualitative basis the polysulphone membrane was affected by the surfactants and more by the aromatic ones. The effect was not due to concentration polarization.

Surfactant-induced phytotoxicity: evidence for interaction with epicuticular wax fine structure

Phytotoxicity of two homologous series of non-ionic surfactants [octylphenoxy polyethoxyethanol (OP), α-[4-(1,1,3,3-tetramethylbutyl) phenyl]-ω-hydroxypoly-(oxy-1,2-ethanediyl) and nonylphenoxy polyethoxyethanol (NP), α-(nonylphenol)-ω-hydroxypoly-(oxy-1,2-ethanediyl)], of varying oxyethylene (EO) chain length was studied in Brassica oleracea var. gongylodes (L.). Surfactant toxicity following foliar application was determined by visual rating of leaf damage and measurement of ethylene production. Surfactants of medium EO chain length (9.5 and 10 EO) were most phytotoxic; phytotoxicity decreased with decrease to 5 EO or increase to 30 EO. No difference in phytotoxicity was found between OP and NP surfactants. Ethylene production 12 h after application increased with increasing surfactant concentration (0.01–1% w/v) and was greater for droplets of 1.0 μl than for those of 0.5 μl. Regardless of droplet size and surfactant concentration, application of OP+9.5EO enhanced ethylene production more than OP+5EO. After disruption of epicuticular wax fine structure or removal of epicuticular wax, ethylene production following OP+5EO application was significantly greater than that with OP+9.5EO. In Hordeum vulgare (L.), Triticum aestivum (L.) and Vicia faba (L.), OP+5EO induced highest ethylene production, whereas in Brassica napus var. napus (L.) and Brassica oleracea var. gemmifera (DC.) OP+9.5EO was most phytotoxic. Surfactant phytotoxicity is discussed in relation to wetting characteristics of microrough leaf surfaces of Brassica species.

Vesicle to Micelle Transitions of Egg Phosphatidylcholine Liposomes Induced by Nonionic Surfactants, Poly(oxyethylene) Cetyl Ethers1

Vesicle to micelle transitions of sonicated liposomes of egg yolk phosphatidylcholine (EPC) induced by a homologous series of nonionic surfactants, poly(oxyethylene) cetyl ethers [POE(n) cetyl ether], were investigated by using the method of turbidity titrations. The turbidities of the mixed dispersions of sonicated vesicles and surfactant were systematically measured as a function of the surfactant added for a wide range of lipid concentrations (from 0.51 to 6.35 mM EPC). From the titration curves, two threshold points representing onset and complete solubilization of liposomal membranes were determined as a probe for the effect of the length of ethylene oxide (EO) moiety on the phase behavior of ternary system of POE(n) cetyl ethers-EPC-excess water. Patterns of turbidity curves and the surfactant concentrations at two threshold points as well as widths of region between two transitions, where lamellar sheets and mixed micelles may coexist, mainly depended on the length of EO head group. With changing the lengths, solubilization of liposomes and phase diagram showed optimal behavior. That is, in the middle range of EO numbers, it resulted in narrowest coexistence region between onset and complete solubilization. Assuming the equilibrium partitioning model, critical effective molar ratios of surfactant to lipid, Rsat, free surfactant concentrations, Dw, and the partition coefficient of surfactant between bilayer and aqueous phase, K, in surfactant-saturated liposomes were quantitatively determined as a function of EO number. Effective ratios, Rsol, and free surfactant concentration in mixed micelles were also determined. In addition, the effects of CMC and HLB of surfactants on the solubilization of liposome were discussed.

Effect of non-ionic surfactants on ethylene release and leaf growth of Phaseolus vulgaris L.

Effects of three different homologous series of non-ionic surfactants (octylphenolethoxylates, non-ylphenolethoxylates, linear alcoholethoxylates), which are commonly used in formulations of foliar-applied agrochemicals, on ethylene (C 2H 4) release and growth of primary leaves were investigated in Phaseolus vulgaris L. cultivar ‘Processor’ plants. Surfactants varied with respect to ethylene oxide (EO) chain length from 3 to 40 mol EO. C 2H 4 production increased significantly when surfactant concentration exceeded 0.5%; however, the same surfactant (octylphenolethoxylate (OP) with 9.5 mol EO) depressed growth of primary leaves at a concentration as low as 0.01%. C 2H 4 release was inversely related to EO content of the surfactant molecule. Generally, growth rates of primary leaves were lowest when leaves were treated with surfactants (0.1%) of low to medium EO chain length (3 to 11 EO). The more hydrophilic surfactants (> 20 EO) had the smallest impacts both on C 2H 4 evolution and leaf growth. The induction of physiological effects and their importance for formulation practice is discussed.

Possibility of analytical application of the partition in aqueous biphasic polymeric systems technique

The partition behaviour of a number of ionic and nonionic surface-active substances in the dextran-polyethylene glycol system was examined. The strictly linear dependence of the logarithm of the partition coefficient on the alkyl chain length for a homologous series of nonionic surfactants provides a measure of the difference in the relative hydrophobicity between the two phases of the system, in terms of the free energy of transfer of a CH 2 group from the bottom phase to the top phase of the system. This difference is found to be altered in the presence of NaCl or KCl depending on the salt concentration. It is concluded that the influence of the salt composition of the system on the distributed solutes' behaviour may be due to the effect of the ions on the hydrophobicity difference between the phases. The partition of ionic amphiphiles is found to be dependent on the relative hydrophobicity of the compounds as well as on their charge. It is shown that at salt concentrations up to about 0.1 M NaCl the charged solute partition is determined by its charge as well as its relative hydrophobicity, in the presence of 0.1–0.2 M NaCl the substance distribution is highly dependent on its charge and slightly on its lipophility. At the salt concentrations above 0.2 M the solute partition is determined just by its hydrophobic character and seems to be totally independent of its charge. It is concluded that the partition technique can be used for analytical purposes. The method seems to be unique in providing quantitative information on the amphiphilic surface properties of the solutes being partitioned.

Hydrophilic-lipophilic balance and surface film state of nonionic surfactants

The polarographic study on the effect of nonionic surfactants on the damping of oxygen maximum confirms the validity ofVan Voorst Vader's rule and a major part which play the hydrophilic-lipophilic balance of surfactant molecules in surface phenomena. On this basis the simple relationships are presented between the molecular area in surface film (A) andGriffin's andDavies' HLB. It is shown that at a specific pressure theA increases with increasing HLB values for homologous series of nonionic surfactants. The limitations of the validity of the relations derived with respect to the specific surface pressure chosen are also considered.

Relative Toxicity of Three Homologous Series of Nonionic Surfactants in the Planarian

An investigation on the toxicity of three homologous series of nonionic surfactants was carried out using planarian Dugesia lugubris (O. Schmidt). The surfactants used in this study were polyoxyethylene stearic acid esters, polyoxyethylene sorbitan fatty acid partial esters, and polyoxyethylene alkyl ethers. The effect of surfactant concentration (C) on time of death (T) of planarian can be described by a regression equation, where 1/T is linearly related to C. Analysis of variance of 1/T showed that each regression was highly significant and that deviations from linearity were not significant. The behavior of the polyoxyethylene stearic acid esters and polysorbates was in good agreement with the Levy-Gucinski theory, which describes the effect of toxic agents on goldfish. No agreement with the same theory was shown by surfactants of the polyoxyethylene alkyl ethers, whose regression lines, in the C range 0.05-1.0%, failed to intersect the origin. Statistical differences in relative toxicity between the members of each series were assessed. In the polyoxyethylene stearic acid esters, a linear relationship between the length of the polyoxyethylene chain and lethal time was detected. Relative toxicity in the polysorbates decreases in the order of the 20, 40, 60, and 80 esters, thereby depending on the nature of the esterifying acid (lauric, palmitic, stearic, and oleic, respectively). No clear-cut pattern was found with the polyoxyethylene alkyl ethers; differences in relative toxicity between the ethers of the series were not statistically significant. The present study is indicative of the utility of the planarian in biopharmaceutical research.