Nonionic surfactants with linear and branched hydrocarbon tails: compositional analysis, phase behavior, and film properties in bicontinuous microemulsions

Nonionic alcohol ethoxylates are widely used as surfactants in many different applications. They are available in a large number of structural varieties as technical grade products. This variety is mainly based on the use of different alcohols, which can be linear or branched and contain primary, secondary, or tertiary OH groups. Technical grade products are poorly defined as they are composed of alcohol mixtures being different in chain length and structure. On the other hand, monodisperse alcohol ethoxylates are commercially available; however, these surfactants exist only with primary and linear alcohols. In the field of microemulsion research the monodisperse alcohol ethoxylates are widely used. The phase behavior and film properties of these surfactants were studied intensively with respect to the size of the hydrophilic and hydrophobic moieties. Due to the lack of appropriate model surfactants until now, there is little information on how the structure of the hydrocarbon tail influences the microemulsion behavior. To examine structural influences, we synthesized a series of surfactants with the composition C10E5 and having different linear and branched hydrocarbon tails. The surfactants were monodisperse with respect to the hydrocarbon tail but polydisperse with respect to the ethoxylation degree. However, a detailed characterization showed that they were similar concerning the average ethoxylation degree and EO chain length distribution. The phase behavior was investigated for bicontinuous microemulsions, and the film properties were analyzed by small-angle neutron scattering (SANS). Our results show that the structure of the hydrocarbon tail strongly influences the microemulsion behavior. The most efficient surfactant is obtained if the hydrocarbon tail is linear and the hydrophilic group is attached in the C-1 position. Surfactants having the hydrophilic group bound to the C-2 or C-4 position or which contain a branched hydrocarbon tail are less efficient and exhibit in most cases visibly lower phase inversion temperatures. Both the efficiency and temperature behavior mainly can be explained on the basis of increased bulkiness of the branched structures compared to the fully linear version. The phase behavior results are largely confirmed by the SANS investigations. Those results show that the fully linear surfactant exhibits the most rigid interfacial film. In additional experiments this surfactant was compared with its monodisperse analogue. According to the phase diagrams, the surfactant having the polydisperse hydrophilic moiety is drastically more efficient although the film stiffnesses are almost identical.     

Phase Behavior of Bicontinuous and Water/Diesel Fuel Microemulsions Using Nonionic Surfactants Combined with Hydrophilic Alcohol Ethoxylates

Bicontinuous and water-in-diesel microemulsions were formulated using single nonionic alkyl poly glycol ethers combined with hydrophilic alcohol ethoxylates. The phase behavior at temperatures ranging from 0°C to 50°C was investigated. Visual inspection as well as cross-polarizers were used to detect anisotropy. The fish phase diagrams were determined. The presence of the hydrophilic alcohol ethoxylates was necessary to initiate both types of microemulsions. Increasing the hydrophobic chain length of the surfactant led to a wider range of temperature stability at lower surfactant concentration. Meanwhile, increasing the ethylene oxide units in the headgroup by two units led to a phase diagram that is dominated by lyotropic liquid crystal. The formulated water in diesel microemulsions were tested experimentally in a 4-cylinder diesel engine. From this it is observed that the emissions of NO_x, soot, and CO₂ were reduced substantially compared to neat diesel, while for the CO the reduction occurs just at low load.      

添加剂对非离子十二烷基聚氧乙烯聚氧丙烯醚浊点的影响

测定了无机盐、单元及多元醇、有机酸及离子型表面活性剂对3种非离子表面活性剂十二烷基聚氧乙烯聚氧丙烯醚C₁₂H₂₅(EO)_m(PO)_nH(LS₃₆,m=3,n=6;LS45,m=4,n=5;LS54,m=5,n=4)浊点的影响.     

Amphiphilic polylactide-poly(ethylene oxide)-poly(propylene oxide) block copolymers: Self-assembly behavior and cell affinity

Polylactide (PLA) is a biodegradable polyester recognized for its potential use as a biomedical material. Poly(ethylene oxide) (PEO) and copolymers based on PEO and poly(propylene oxide) (PPO) are biocompatible polyethers widely applied in the biomedical field, particularly as macromolecular nonionic surfactants. In this work, PLA blocks were attached to the PEO and to the PEO and PPO-based triblock copolymer PEO–PPO–PEO, through ring-opening polymerization of racemic lactide (rac-LA) to obtain the amphiphilic triblock PLA–PEO–PLA and pentablock PLA–PEO–PPO–PEO–PLA copolymers containing hydrophilic/hydrophobic blocks with variable block mass ratios. The copolymers were evaluated for chemical composition, molar mass, and thermal properties, and they were used to prepare self-assemble aggregates in water from tetrahydrofuran polymer solutions. The combination of scattering light experiments and microscopy techniques revealed the spherical morphology of the aggregates with diameters around 180–200 nm, which comprises a hydrophobic PLA core and a hydrophilic polyether shell. The aggregates are nontoxic to human cervical cancer cell line — HeLa cells, as determined by MTS assay, and the aggregates are potential candidates to be applied in the encapsulation of hydrophobic compounds. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 2203–2213     

MICROEMULSION SYSTEMS WITH A NONIONIC COSURFACTANT

The conditions to obtain W/0 microemulsions using ionic surfactants and a nonionic cosurfactant, a polyoxyethylene alkyl ether, were investigated. The length of the polyoxyethylene chain was critical to obtain the typical water solubilization maximum

The variation of the W/0 microemulsion region with hydrocarbon content was different from that of the usual type of microemulsions having a medium chain length alcohol as cosurfactant. In the present systems the W/0 microemulsion region was not a direct continuation of the inverse micellar area at zero content of hydrocarbon. Addition of hydrocarbon was necessary for the formation of inverse micelles

The microemulsion regions were sensitive to the kind of hydrocarbon used; a sign of the importance of the nonionic surfactant for the stability of this kind of microemulsions.     

A Monitoring System for Selective Determination of Alkylphenol Ethoxylates by the Adsorptive Stripping‐Indirect Tensammetric Technique

A new monitoring system for the adsorptive stripping‐indirect tensammetric technique has been developed. The system responded selectively to alkylphenol ethoxylates having 5–14 oxyethylene subunits (APE) (being a fraction of nonionic surfactants). It consists of 20 ppm of Mannoxol OT and 20 ppb of tetrabutylammonium bromide (TBAB). In the presence of APE a tensammetric peak of the monitoring mixture is growing. A calibration plot has a slightly sigmoidal shape; the dynamic response range is from 0.5 to 2.0 μg and the detection limit is 0.075 μg. APE determination is highly tolerant to alcohol ethoxylates (AE) having a C18 hydrophobic part, however, the tolerance of AE having a C12 hydrophobic part is small (the APE signal is only three times higher than that of AE having a C12 hydrophobic part). An analytical response to a mixture consisting different nonionic surfactants (NS) is approximately additive. The developed monitoring system was applied to the determination of an APE fraction in 14 river water samples. NS were separated from the water matrix by liquid‐liquid extraction with chloroform. The recovery of Triton X‐100 spike was 102% and the precision 6.5%.     

混合表面活性剂微乳状液的形成和相行为研究进展

讨论了单一表面活性剂,混合表面活性剂,助溶剂等对油／水微乳状液的形成和相行为的影响。对混合表面活性剂微乳状液的形成和相行为研究工作进行了归纳和总结,重点分析了正负离子表面活性剂微乳状液的相行为和表面活性剂微乳状液的相行为和表面活性剂效率,讨论了微乳状液形成的影响因素,并提出了这一研究领域可能的发展前景。     

Microemulsification of triglyceride sebum and the role of interfacial structure on bicontinuous phase behavior

A unique triblock surfactant is reported that allows for the efficient microemulsification of triglycerides. Unlike the results of all previous efforts, these triglyceride microemulsions can be formed without the use of cosurfactants or dilution with co-oils and follow the classical patterns of surfactant phase behavior exhibited by mixtures of water, alkane oils, and nonionic oligoethylene glycol surfactants, i.e., progression from oil/water emulsions to one-phase microemulsions to water/oil emulsions with increasing temperature. Lamellar phases that usually dominate the aqueous phase behavior of surfactant/triglyceride mixtures are suppressed, allowing for the formation of single-phase microemulsions containing equal amounts of triglyceride and water. These isotropic and low-viscous fluids are particularly useful for cleansing and delivery of functional ingredients in skin care products. The effects of mixing a variety of typical skin care ingredients and components of sebum (skin oil) were also explored. Fatty acids significantly reduce the average microemulsion temperature, while other ingredients and oils, which do not partition at the oil/water interface, have less impact on the phase behavior. In all cases, one-phase microemulsions containing equal amounts of oil and water can be formed even at high additive concentrations. Indeed, partial replacement oftriglyceride with any of the additives examined consistently reduced the amount of surfactant necessary to form single-phase microemulsions. However, the greatest boost in surfactant efficiency was found with the addition of medium molecular weight amphiphilic block copolymers.     

Interaction of amphiphilic block copolymer micelles with surfactants

An out line and summary of literature studies on interactions between different types of amphiphilic copolymer micelles with surfactants has been given. This field of research is still emerging and it is difficult presently to make generalisations on the effects of surfactants on the copolymer association. The effects are found to be varied depending upon the nature and type of hydrophobic (hp) core and molecular architecture of the copolymers and the hydrocarbon chain length and head group of surfactants. The information available on limited studies shows that both anionic and cationic surfactants (in micellar or molecular form) equally interact strongly with the associated and unassociated forms of copolymers. The beginning of the interaction is typically displayed as critical aggregation concentration (CAC), which lies always below the critical micelle concentration of the respective surfactant. The surfactants first bind to the hydrophobic core of the copolymer micelles followed by their interaction with the hydrophilic (hl) corona parts. The extent of binding highly depends upon the nature, hydropobicity of the copolymer molecules, length of the hydrocarbon tail and nature of the head group of the surfactant. The micellization of poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–poly(ethylene oxide) was found to be suppressed by the added surfactants and at higher surfactant concentrations, the block copolymer micelles get completely demicellized. This effect was manifested itself in the melting of liquid crystalline phases in the high copolymer concentrations. However, no such destabilization was found for the micelles of polystyrene (PS)–poly(ethylene oxide) copolymers in water. On the contrary, the presence of micellar bound surfactant associates resulted in to large super micellar aggregates through induced intra micellar interactions. But with the change in the hydrophobic part from polystyrene to poly(butadiene) (PB) in the copolymer, the added surfactants not only reduced the micellar size but also transformed cylindrical micelles to spherical ones. The mixtures in general exhibited synergistic effects. So varied association responses were noted in the mixed solutions of surfactants and copolymers.     

New amphiphilic diblock copolymers: surfactant properties and solubilization in their micelles

Several series of amphiphilic diblock copolymers are investigated as macrosurfactants in comparison to reference low-molar-mass and polymeric surfactants. The various copolymers share poly(butyl acrylate) as a common hydrophobic block but are distinguished by six different hydrophilic blocks (one anionic, one cationic, and four nonionic hydrophilic blocks) with various compositions. Dynamic light scattering experiments indicate the presence of micelles over the whole concentration range from 10(-4) to 10 g x L(-1). Accordingly, the critical micellization concentrations are very low. Still, the surface tension of aqueous solutions of block copolymers decreases slowly but continuously with increasing concentration, without exhibiting a plateau. The longer the hydrophobic block, the shorter the hydrophilic block, and the less hydrophilic the monomer of the hydrophilic block is, the lower the surface tension is. However, the effects are small, and the copolymers reduce the surface tension much less than standard low-molar-mass surfactants. Also, the copolymers foam much less and even act as anti-foaming agents in classical foaming systems composed of standard surfactants. The copolymers stabilize O/W emulsions made of methyl palmitate as equally well as standard surfactants but are less efficient for O/W emulsions made of tributyrine. However, the copolymer micelles exhibit a high solubilization power for hydrophobic dyes, probably at their core-corona interface, in dependence on the initial geometry of the micelles and the composition of the block copolymers. Whereas micelles of copolymers with strongly hydrophilic blocks are stable upon solubilization, solubilization-induced micellar growth is observed for copolymers with moderately hydrophilic blocks.     

Formation of fluorinated nonionic surfactant microemulsions in hydrofluorocarbon 134a (HFC 134a)

A structurally related series of fluorinated nonionic oxyethylene glycol surfactants of the type C(m)F(2m+1)(CH(2))(n)O[(CH(2)CH(2)O)(p)H], denoted C(m.n)E(p) (where m=4, 6, or 7, m=1 or 2, and p=4 or 6) were synthesized and their surface behavior in aqueous solution was characterized. The ability of these surfactants to form water-in-hydrofluorocarbon (HFC) propellant 134a microemulsions suitable for use in the aerosolized delivery of water-soluble drugs has been investigated. Phase studies showed that, regardless of the composition used, clear one-phase systems could not be prepared if a fluorinated nonionic surfactant was used alone, or in combination with a short or medium fluorocarbon alcohol cosurfactant. Clear one-phase systems could, however, be prepared if a short-chain hydrocarbon alcohol, such as ethanol, n-propanol, or n-pentanol, was used as cosurfactant, with the extent of the one-phase region increasing with decreased chain length of the alcohol cosurfactant. Light-scattering studies on a number of the hydrocarbon-alcoholcontaining systems in the propellant-rich part of the phase diagram showed that only systems prepared with C(4.2)E(6) and propanol contained microemulsion droplets (all other systems investigated were considered to be cosolvent systems).     

SELF-ASSEMBLING AMPHIPHILIC POLYELECTROLYTES AND THEIR NANOSTRUCTURES

The self-assembling behavior of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS)and hydrophobic comonomers possessing dodecyl groups linked by various spacer bonds was discussed with a focus on theeffect of the spacer. The characterization of association behavior of such polymers in water using quasielastic light scattering,capillary electrophoresis, NMR relaxation, various fluorescence, and viscoelastic methods was described. These copolymersform a variety of self-assembled nanostructures depending on the type of the spacer. Random copolymers of AMPS and N-dodecylmethacrylamide show a strong preference for intrapolymer self-association even in concentrated aqueous solutionsforming single-macromolecular self-assemblies (unimolecular micelles). In contrast, random copolymers of AMPS anddodecyl methacrylate are prone to undergo interpolymer associations yielding multipolymer micelles. In random copolymersof AMPS and a methacrylate substituted a nonionic surfactant (HO(CH_2CH_2O)_(25)C_(12)H_(25)) (C_(12)E_(25)), dodecyl groups are muchless restricted by the polymer backbone because they are linked via a long, flexible hydrophilic spacer. Thus, the polymer-bound C_(12)E_(25) surfactant moieties form micelles similar to those formed by discrete surfactants, but they are bridged bypolymer chains forming a network structure.     

碳氢表面活性剂在超临界CO2中形成微乳液的研究进展

在超临界CO₂中形成微乳液可以克服CO₂对高分子量和亲水性物质溶解能力差的缺点。碳氢表面活性剂成本低,对环境友好,利用碳氢表面活性剂形成超临界CO₂微乳液有利于工业应用,但绝大部分碳氢表面活性剂不能形成微乳液,所以需要对碳氢表面活性剂进行选择和设计。本文介绍了微乳液的形成、表征和评价,从表面活性剂的亲CO₂性能和界面活性两方面,综述了碳氢表面活性剂的设计思想和进展。另外介绍了助表面活性剂对形成超临界CO₂微乳液的作用,并对常规碳氢表面活性剂在助表面活性剂的作用下形成超临界CO₂微乳液的体系进行了综述。最后,介绍了含碳氢表面活性剂的混合表面活性剂在形成超临界CO₂微乳液方面的研究情况。     

Novel nonionic polymerisable surfactants based on sulfoxides. 1. Monomer synthesis and general surfactant behaviour

The synthesis, surface activity, and micellisation of a series of new nonionic polymerisable surfactants, often referred to as surfmers, are described. These monomers bear terminal vinyl groups or acrylic esters, and the nonionic sulfoxide moiety. Compared to many other nonionic hydrophilic fragments, the sulfoxide group behaves as a strongly hydrophilic fragment of small volume, that can balance up to an acryloyloxyundecyl hydrophobic chain. The incorporation of the polar acrylate moiety at the end of the hydrophobic chain seems to confer surfactant properties similar to the ones of bola amphiphiles to the monomers. Received: 22 March 2001 Accepted: 11 August 2001     

Microcalorimetric study on micellization of nonionic surfactants with a benzene ring or adamantane in their hydrophobic chains

The micellization of a novel family of nonionic surfactants poly(oxyethylene) glycol alkyl ethers has been studied by microcalorimetry. One of the surfactants has adamantane, and the other nonionic surfactants have a benzene ring in their hydrophobic chains, which moves from the terminal of the hydrophobic chain toward the headgroup. Moreover, the alkyl chain of the nonionic surfactants is straight or branched. Both the critical micelle concentration (cmc) and the thermodynamic parameters associated with the micelle formation have been obtained. The cmc decreases and the enthalpy of micelle formation (deltaH(mic)) becomes less positive gradually as the length of hydrophobic chain increases, whereas the values of cmc and deltaH(mic) tend to increase for the surfactants with a longer ethylene oxide chain. However, the deltaH(mic) value of the surfactant with seven carbon atoms in a hydrophobic chain is more positive than that of the surfactant with six carbon atoms in a hydrophobic chain. Comparing with the nonionic surfactant with a methylene hydrophobic chain, the surfactants with benzene rings and adamantane groups have larger cmc values and the cmc values increase with the size of the groups. Furthermore, moving the phenyl group from the terminal of the hydrophobic chain to the neighbor of the hydrophilic headgroup leads to the decreased cmc. Both the variation of hydrophobic interaction from the movement of phenyl group and pi-pi interaction among adjacent phenyl groups affect deltaH(mic) values.     

Functional polythiiranes 7: Surface activity of polythiiranes with PEO side chains

 Some comb-like polythiiranes with PEO side chains were prepared from the corresponding macromonomers. These new materials are amphiphiles and act as surfactants. Their surface tension and interfacial tension are measured and studied in this paper on account of their structures. The lowering of surface tension measured in polymers bearing methyl terminal group in PEO side chains, are in the same range as these observed with polymers of identical structures but different main chains. An increase of the hydrophobic units in the main chain, obtained in copolymers with methylthiirane does not significantly modified the surface tensions. Better lowering is afforded with structures bearing large alkyl groups as terminal group of PEO side chains. On the contrary, some of these macro-molecules with an optimized EO content largely lower the water/xylene surface tension. The main interest of these new materials is their very low cmc and the stabilization of L₁-type microemulsions. Received: 20 May 1997 Accepted: 25 November 1997     

Effect of surfactant additives on the size and morphology of ammonium and potassium nitrate particles obtained by crystallization from reverse micellar solutions of tergitol NP-4

Effect of small additives of hydrophilic and hydrophobic surfactants (sodium dodecyl sulfate, cetyltrimethylammonium bromide, Span-80, and AOT) on the size and morphology of particles of ammonium and potassium nitrate powders prepared by isothermal bulk crystallization from reverse micellar solutions of Tergitol NP-4 in decane and diesel fuel was studied. Initial microemulsions were characterized by photon correlation spectroscopy, powders were described by scanning electron microscopy, energy dispersion X-ray analysis, microanalysis, and flame photometry. In the context of increase of powder dispersity, hydrophobic anionic AOT was found to be promising additive, it produces whisker-type particles 5–10 μm long and 0.1–0.5 μm thick.     

A nucleophilic substitution reaction performed in different types of self-assembly structures

A nucleophilic substitution reaction between 4-tert-butylbenzyl bromide and potassium iodide has been performed in oil-in-water microemulsions based on various C12Em surfactants, i.e., dodecyl ethoxylate with m number of oxyethylene units. The reaction kinetics was compared with the kinetics of reactions performed in other self-assembly structures based on very similar surfactants and in homogeneous liquids. The reaction was fastest in the micellar system, intermediate in rate in the microemulsions, and most sluggish in the liquid crystalline phase. Reaction in a Winsor I system, i.e., a two-phase system comprising an oil-in-water microemulsion in equilibrium with excess oil, was equally fast as reaction in a one-phase microemulsion. The reactions in microemulsion were surprisingly fast compared to reaction in homogeneous, protic liquids such as methanol and ethanol. The rate was independent of the microstructure of the microemulsion; however, the rate was very dependent on the type of surfactant used. When the C12Em surfactant was replaced by a sugar-based surfactant, octyl glucoside, the reaction was much more sluggish. The high reactivity in microemulsions based on C12Em surfactants is belived to be due to a favorable microenvironment in the reaction zone. The reaction is likely to occur within the surfactant palisade layer, where the water activity is relatively low and where the attacking species, the iodide ion, is poorly hydrated and, hence, more nucleophlic than in a protic solvent such as water or methanol. Sugar surfactants become more hydrated than alcohol ethoxylates and the lower reactivity in the microemulsion based on the sugar surfactant is probably due to a higher water activity in the reaction zone.     

Mixed micelles of polyethylene glycol (23) lauryl ether with ionic surfactants studied by proton 1D and 2D NMR

(1)H NMR chemical shift, spin-lattice relaxation time, spin-spin relaxation time, self-diffusion coefficient, and two-dimensional nuclear Overhauser enhancement (2D NOESY) measurements have been used to study the nonionic-ionic surfactant mixed micelles. Cetyl trimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) were used as the ionic surfactants and polyethylene glycol (23) lauryl ether (Brij-35) as the nonionic surfactant. The two systems are both with varying molar ratios of CTAB/Brij-35 (C/B) and SDS/Brij-35 (S/B) ranging from 0.5 to 2, respectively, at a constant concentration of 6 mM for Brij-35 in aqueous solutions. Results give information about the relative arrangement of the surfactant molecules in the mixed micelles. In the former system, the trimethyl groups attached to the polar heads of the CTAB molecules are located between the first oxy-ethylene groups next to the hydrophobic chains of Brij-35 molecules. These oxy-ethylene groups gradually move outward from the hydrophobic core of the mixed micelle with an increase in C/B in the mixed solution. In contrast to the case of the CTAB/Triton X-100 system, the long flexible hydrophilic poly oxy-ethylene chains, which are in the exterior part of the mixed micelles, remain coiled, but looser, surrounding the hydrophobic core. There is almost no variation in conformation of the hydrophilic chains of Brij-35 molecules in the mixed micelles of the SDS/Brij-35 system as the S/B increases. The hydrophobic chains of both CTAB and SDS are co-aggregated with Brij-35, respectively, in their mixed micellar cores.     

Foaming and foam stability for mixed polymer-surfactant solutions: effects of surfactant type and polymer charge

Solutions of surfactant-polymer mixtures often exhibit different foaming properties, compared to the solutions of the individual components, due to the strong tendency for formation of polymer-surfactant complexes in the bulk and on the surface of the mixed solutions. A generally shared view in the literature is that electrostatic interactions govern the formation of these complexes, for example between anionic surfactants and cationic polymers. In this study we combine foam tests with model experiments to evaluate and explain the effect of several polymer-surfactant mixtures on the foaminess and foam stability of the respective solutions. Anionic, cationic, and nonionic surfactants (SDS, C(12)TAB, and C(12)EO(23)) were studied to clarify the role of surfactant charge. Highly hydrophilic cationic and nonionic polymers (polyvinylamine and polyvinylformamide, respectivey) were chosen to eliminate the (more trivial) effect of direct hydrophobic interactions between the surfactant tails and the hydrophobic regions on the polymer chains. Our experiments showed clearly that the presence of opposite charges is not a necessary condition for boosting the foaminess and foam stability in the surfactant-polymer mixtures studied. Clear foam boosting (synergistic) effects were observed in the mixtures of cationic surfactant and cationic polymer, cationic surfactant and nonionic polymer, and anionic surfactant and nonionic polymer. The mixtures of anionic surfactant and cationic polymer showed improved foam stability, however, the foaminess was strongly reduced, as compared to the surfactant solutions without polymer. No significant synergistic or antagonistic effects were observed for the mixture of nonionic surfactant (with low critical micelle concentration) and nonionic polymer. The results from the model experiments allowed us to explain the observed trends by the different adsorption dynamics and complex formation pattern in the systems studied.