Comparative studies on the micellization of sodium bis(4-phenylbutyl) sulfosuccinate and sodium bis(2-ethylhexyl) sulfosuccinate and their interaction with hydrophobically modified poly(acrylamide)

The micellization process of sodium bis(4-phenylbutyl) sulfosuccinate (SBPBS) has been studied compared to that of sodium bis(2-ethylhexyl) sulfosuccinate (AOT) by surface tension, steady-state fluorescence, microcalorimetry, dynamic light scattering (DLS), and transmission electron microscopy (TEM) measurements. Meanwhile, the interaction of these two surfactants with hydrophobically modified poly(acrylamide) (HMPAM) was investigated. The results show that the surface tension at the critical micelle concentration (cmc) of SBPBS and the micropolarity probed by pyrene in SBPBS aggregates are both larger than those of AOT. The enthalpy change of micellization (DeltaH(mic)) of AOT is endothermic, while it is exothermic for SBPBS. Strong pi-pi interaction among the adjacent phenyl groups of SBPBS molecules is likely the cause for the above properties of SBPBS. Moreover, vesicles are observed for AOT and SBPBS by DLS and TEM, especially for AOT, whose micelle-vesicle transition has been first confirmed by its calorimetric curve. In the surfactant-HMPAM systems, the critical aggregation concentration (cac), the saturation concentration of aggregation (C(2)), and the thermodynamic parameters of binding have also been determined. The conclusion may be drawn that the binding strength of SBPBS onto HMPAM is stronger than that of AOT.     

混合表面活性剂在非极性溶剂中的聚集行为

表面活性剂在非极性溶剂中的聚集行为比在水溶液中复杂得多. 水溶液中表面活性剂有一明确的临界胶束浓度(CMC),而在非极性溶剂中至今对CM C概念仍有怀疑^[1], 但已有多种手段如染料增溶法、水增溶法、光散射法、荧光偏振、紫外和核磁共振谱等证实并测定了非极性溶剂中 CMC 的存在^[1～5]. 表面活性剂在非极性溶剂中以非离子化状态存在, 其缔合主要靠两亲分子之间的偶极-偶极以及离子对相互作用, 那么在一种表面活性剂溶液中加入另一种表面活性剂, 即表面活性剂的复配, 必然对其聚集行为产生重大影响, 但迄今为止, 尚未见关于混合表面活性剂在非极性溶剂中聚集行为的报道. 本文采用碘光谱法和水增溶法测定了阴离子表面活性剂AOT 和非离子表面活性剂 Brij30 混合后在正庚烷中形成反胶束的 CMC, 以期考察表面活性剂的复配对其聚集行为的影响。     

Effect of water-soluble polymers on the morphology of aerosol OT vesicles

Vesicles of different morphologies were found to form in aqueous solutions of the surfactant sodium bis(2-ethylhexyl)sulfosuccinate, AOT, and in binary mixtures composed of AOT with poly(ethylene glycol) and poly(sodium 4-styrenesulfonate). Using electrical conductivity and fluorescence probing, two critical vesicle concentrations, cvc and cac, were determined. These critical aggregation concentrations correspond to different kinds of aggregates, which are easily observed by optical microscopy.     

Interactions of mixed surfactant solution with liposome membrane

Interactions of the mixed surfactant solution of dodecylamido propyl dimethyl aminoacetate and sodium dodecyl sulfate with the liposomal membrane were studied. Lytic activities of the surfactants were measured as a function of the concentrations of surfactant and phospholipid and the composition of mixed surfactants. The solubilization limits of phospholipid by surfactants were determined from the change of their aggregation behavior in suspensions at equilibrium by means of quasi-elastic light scattering. The mixed surfactant solutions showed lower lytic activity than single component surfactant solution in spite of the strong adsorption onto the liposome surface. This was attributed to low solubilization power of binary mixture for phospholipid.     

AOT/水/甲苯微乳体系的第二维里系数和液滴间的相互作用

在一系列温度下通过对水与丁二酸双(2-乙基己基)酯磺酸钠(AOT)摩尔比为12、不同浓度的AOT/水/甲苯微乳液进行静态光散射测量, 获得液滴的相对分子质量、AOT的聚集数、液滴半径和不同温度下的第二维里系数. 利用第二维里系数与温度的关系获得液滴的相互作用焓和熵, 分别为-4.03×10⁴ J·mol^-1和-139.8 J·mol^-1·K^-1, 说明AOT/水/甲苯微乳液滴间表面活性剂疏水链相互交叉渗透的能量变化为负值, 交叉渗透为焓驱动.     

Solubilization by different-sized surfactant mixtures

The solubilization phenomenon was investigated in mixed surfactant systems. The solubilization power of a mixed surfactant reaches its maximum at a particular temperature at each mixing ratio of surfactants. When the mole fraction of C4E1 in the total surfactant (w1 value) was varied in a water/C12E5/C4E1/decane system, the minimum mole fraction of total surfactant in the system necessary to obtain a single microemulsion phase (xi value) was almost unchanged for w1<0.3, whereas it increased remarkably for w1>0.8. The molar solubilization capacity (Cs=(1-xi)/xi) of the mixed surfactant decreased remarkably for w1<0.3, whereas it decreased gradually for w1>0.8. The result [Formula: see text] is due largely to the characteristic of the function xi(Cs)=1/(1+Cs), specifically, [Formula: see text] , where dxi/dw1=(dxi/dCs)(dCs/dw1). The partial molar solubilization capacity (Cs) of C4E1 was negative at almost all w1, but the Cs value of C12E5 went through a maximum on the addition of C4E1. Propanol (a cosurfactant) has the same effect on the solubilization phenomenon in the water/C12E6/propanol/heptane system. In the water/C12E5/C12E7/decane system, the Cs value of each surfactant did not vary greatly as the mixing ratio of surfactants was varied. The Cs and xi values were close to molar additivity for each mixing ratio.     

Binding of sodium dodecyl sulfate and hexaethylene glycol mono-n-dodecyl ether to the block copolymer L64: electromotive force, microcalorimetry, surface tension, and small angle neutron scattering investigations of mixed micelles and polymer/micellar surfactant complexes

The interactions of sodium dodecyl sulfate (SDS) with the triblock copolymer L64 (EO13-PO30-EO13) and hexaethylene glycol mono-n-dodecyl ether (C12EO6) were studied using electromotive force, isothermal titration microcalorimetry, differential scanning microcalorimetry, and surface tension measurements. In certain regions of binding, mixed micelles are formed, and here we could evaluate an interaction parameter using regular solution theory. The mixed micelles of L64 with both SDS and C12EO6 exhibit synergy. When L64 is present in its nonassociated state, it forms polymer/micellar SDS complexes at SDS concentrations above the critical aggregation concentration (cac). The cac is well below the critical micellar concentration (cmc) of pure SDS, and a model suggesting how bound micelles are formed at the cac in the presence of a polymer is described. The interaction of nonassociated L64 with C12EO6 is a very rare example of strong binding between a nonionic surfactant and a nonionic polymer, and C12EO6/L64 mixed micelles are formed. We also carried out small angle neutron scattering measurement to determine the structure of the monomeric polymer/micellar SDS complex, as well as the mixed L64/C12EO6 aggregates. In these experiments, contrast matching was achieved by using the h and d forms of SDS, as well as C12EO6. During the early stages of the formation of polymer-bound SDS micelles, SDS aggregates with aggregation numbers of approximately 20 were found and such complexes contain 4-6 bound L64 monomers. The L64/C12EO6 data confirmed the existence of mixed micelles, and structural information involving the composition of the mixed micelle and the aggregation numbers were evaluated.     

Effect of urea on self-organization of sodium N-(11-acrylamidoundecanoyl)-L-valinate in water

In this paper, the hypotheses proposed for the action of urea on the perturbation of molecular assemblies have been tested through studies of the effects of urea on the aggregation properties of a chiral surfactant, sodium N-(11-acrylamidoundecanoyl)-L-valinate in water. Surface tension, fluorescence, and circular dichroism were used to characterize the solution behavior of the amphiphile in the presence of urea. Surface tension measurement indicated decrease of critical aggregation concentration (cac) with the addition of urea in the low concentration range. Fluorescence probe studies using pyrene and 1-anilinonaphthalene indicated solubilization of urea molecules near the aggregate-water interface. Fluorescence anisotropy measurements using 1,6-diphenylhexatriene as probe molecule suggested increase of packing of the hydrocarbon chains of the amphiphiles upon addition of low concentration of urea. Dynamic light scattering measurements showed an increase of the hydrodynamic radius (R(h)) in the presence of increased concentration of urea. At higher concentrations of urea, the R(h) value decreased. Circular dichroism spectra showed the presence of chiral aggregates even in the presence of high concentration of urea.     

Synthesis and characterization of a new gemini surfactant derived from 3alpha,12alpha-dihydroxy-5beta-cholan-24-amine (steroid residue) and ethylenediamintetraacetic acid (spacer)

A new gemini steroid surfactant derived from 3alpha,12alpha-dihydroxy-5beta-cholan-24-amine (steroid residue) and ethylenediamintetraacetic acid (spacer) was synthesized and characterized in aqueous solution by surface tension, fluorescence intensity of pyrene, and light scattering (static and dynamic) measurements. These techniques evidence the existence of a threshold concentration (cac), below which a three layers film is formed at the air-water interface. Above the cac, two types of aggregates--micelles and vesicle-like aggregates--coexist in a metastable state. Filtration of a solution with a starting concentration of 2.6 mM (buffer 150 mM, pH 10) allows isolation of the micelles, which have an average aggregation number of 12, their density being 0.28 g cm(-3). Under conditions where only the vesicle-like aggregates are detected by dynamic light scattering, a value of 5.5 x 10(4) was obtained for their aggregation number at 30 microM, their density being 6.8 x 10(-4) g cm(-3). At high concentrations, the intensity ratio of the vibronic peaks of pyrene, I1/I3, (=0.68) is very close to published values for deoxycholate micelles, indicating that the probe is located in a region with a very low polarity and far from water. A hypothesis to explain the observed aggregation behavior (small aggregates are favored with increasing gemini concentration) is outlined.     

Effect of urea on self-organization of sodium N-(11-acrylamidoundecanoyl)-l-valinate in water

In this paper, the hypotheses proposed for the action of urea on the perturbation of molecular assemblies have been tested through studies of the effects of urea on the aggregation properties of a chiral surfactant, sodium N-(11-acrylamidoundecanoyl)-L-valinate in water. Surface tension, fluorescence, and circular dichroism were used to characterize the solution behavior of the amphiphile in the presence of urea. Surface tension measurement indicated decrease of critical aggregation concentration (cac) with the addition of urea in the low concentration range. Fluorescence probe studies using pyrene and 1-anilinonaphthalene indicated solubilization of urea molecules near the aggregate-water interface. Fluorescence anisotropy measurements using 1,6-diphenylhexatriene as probe molecule suggested increase of packing of the hydrocarbon chains of the amphiphiles upon addition of low concentration of urea. Dynamic light scattering measurements showed an increase of the hydrodynamic radius (R(h)) in the presence of increased concentration of urea. At higher concentrations of urea, the R(h) value decreased. Circular dichroism spectra showed the presence of chiral aggregates even in the presence of high concentration of urea.     

Multilayer vesicles and vesicle clusters formed by the fullerene-based surfactant C60(CH3)5K

The self-assembly behavior of a fullerene-based surfactant, C60(CH3)5K, in water was studied using a combination of static and dynamic light scattering, as well as transmission electron microscopy, and compared to that of the compound C60(C6H5)5K. Both fullerene surfactant systems spontaneously assemble into large vesicles consisting of closed spherical shells formed by bilayers, with critical aggregation concentrations (CAC) lower than 10(-6) g ml(-1). At low concentrations, the aggregate sizes of C60(CH3)5K (radius R approximately 26.8 nm) and C60(C6H5)5K (R approximately 17.0 nm) were found to be substantially different from each other, showing that the change of the substituents surrounding the polar cyclopentadienide head group makes it possible to control the size of the resulting aggregates. Furthermore, the C60(CH3)5K vesicles were found to exist in two qualitatively different types of aggregation with a critical reaggregation concentration (CRC) located at 3.30 x 10(-6) g ml(-1). Above the CRC, larger aggregates were observed (R approximately 37.6 nm), showing a more complex form of supramolecular aggregation, e.g., in terms of multi-bilayer vesicles and/or of clusters of bilayer vesicles.     

SANS studies of the effects of surfactant head group on aggregation properties in water/glycol and pure glycol systems

Aggregation in mixed water-glycol and pure glycol solvents has been investigated with four related surfactants, bearing common C12 tails: anionic, sodium dodecylsulfate (SDS); cationic, dodecyltrimethylammonium bromide (C12TAB); zwitterionic C12-amidopropyldimethylamine betaine (betaine) and nonionic, octaethyleneglycol monododecyl ether (C12E8). The solvent media were water, water/ethylene glycol, and water/propylene glycol mixtures, as well as pure ethylene glycol (EG) and propylene glycol (PG), spanning relative dielectrics epsilon(r) from 79 to 30. Results from small-angle neutron scattering (SANS) experiments, employing deuterated solvents, were consistent with the presence of ellipsoidal, or cylindrical micelles, depending on solvent and surfactant type. In pure EG and PG solvents the ionic and zwitterionic surfactants exhibit only weak aggregation, with much smaller micelles than normally found in water. However, interestingly, pure EG is identified as a solvent in which nonionic C12E8 aggregates strongly, mirroring the behavior in water. In contrast when the solvent is changed to PG (epsilonr=30) aggregation of C12E8 is only minimal. Hence, aggregation is shown to be strongly dependent on surfactant type and identity of the glycol solvent.     

Self-assembly in mixed dialkyl chain cationic-nonionic surfactant mixtures: dihexadecyldimethyl ammonium bromide-monododecyl hexaethylene glycol (monododecyl dodecaethylene glycol) mixtures

The self-assembly of dialkyl chain cationic surfactant dihexadecyldimethyl ammonium bromide, DHDAB, and nonionic surfactants monododecyl hexaethylene glycol, C(12)E(6), and monododecyl dodecaethylene glycol, C(12)E(12), mixtures has been studied using predominantly small-angle neutron scattering, SANS. The scattering data have been used to produce a detailed phase diagram for the two surfactant mixtures and to quantify the microstructure in the different regions of the phase diagram. For cationic-surfactant-rich compositions, the microstructure is in the form of bilamellar, blv, or multilamellar, mlv, vesicles at low surfactant concentrations and is in an L(beta) lamellar phase at higher surfactant concentrations. For nonionic-rich compositions, the microstructure is predominantly in the form of relatively small globular mixed surfactant micelles, L(1). At intermediate compositions, there is an extensive mixed (blv/mlv) L(beta)/L(1) region. Although broadly similar, in detail there are significant differences in the phase behavior of DHDAB/C(12)E(6) and DHDAB/C(12)E(12) as a result of the increasing curvature associated with C(12)E(12) aggregates compared to that of C 12E 6 aggregates. For the DHDAB/C(12)E(12) mixture, the mixed (blv/mlv) L(beta)/L(1) phase region is more extensive. Furthermore, C(12)E(12) has a greater impact upon the rigidity of the bilayer in the blv, mlv, and L(beta) regions than is the case for C(12)E(6). The general features of the phase behavior are also reminiscent of that observed in phospholipid/surfactant mixtures and other related systems.     

Nanoemulsions prepared by a two-step low-energy process

A simple low-energy two-step dilution process has been applied in oil/surfactant/water systems with pentaoxyethylene lauryl ether (C12E5), dodecyldimethylammonium bromide, sodium bis(2-ethylhexyl)sulfosuccinate, sodium n-dodecyl sulfate-pentanol, and hexadecyltrimethylammonium bromide-pentanol. Appropriate formulations were chosen for the concentrate to be diluted with water to generate oil-in-water (O/W) emulsions or nanoemulsions. For the system of decane/C12E5/water, bluish, transparent nanoemulsions having droplet radii of the order of 15 nm were formed, only when the initial concentrate was a bicontinuous microemulsion, whereas opaque emulsions were generated if the concentrate began in an emulsion-phase region. Nanoemulsions generated in the system decane/C12E5/water have been investigated both by dynamic light scattering (DLS) and contrast-variation small-angle neutron scattering (SANS). The SANS profiles show that nanodroplets exist as spherical core-shell (decane-C12E5) particles, which suffer essentially no structural change on dilution with water, at least for volume fractions phi down to 0.060. These results suggest that the nanoemulsion droplet structure is mainly controlled by the phase behavior of the initial concentrate and is largely independent of dilution. A discrepancy between apparent nanoemulsion droplet sizes was observed by comparing DLS and SANS data, which is consistent with long-range droplet interactions occurring outside of the SANS sensitivity range. These combined phase behavior, SANS, and DLS results suggest a different reason for the stability/instability of nanoemulsions compared with earlier studies, and here it is proposed that a general mechanism for nanoemulsion formation is homogeneous nucleation of oil droplets during the emulsification.     

Mixed micelle formation and solubilization behavior toward polycyclic aromatic hydrocarbons of binary and ternary cationic-nonionic surfactant mixtures

Water solubility enhancements of polycyclic aromatic hydrocarbons (PAHs), viz., naphthalene, anthracene and pyrene, by micellar solutions at 25 degrees C using two series of surfactants, each involving two cationic and one nonionic surfactant in their single as well as equimolar binary and ternary mixed states, were measured and compared. The first series was composed of three surfactants, benzylhexadecyldimethylammonium chloride (C16BzCl), hexadecyltrimethylammonium bromide (C16Br), and polyoxyethylene(20)mono-n-hexadecyl ether (Brij-58) with a 16-carbon (C16) hydrophobic chain; the second series consisted of dodecyltrimethylammonium bromide (C12Br), dodecylethyldimethylammonium bromide (C12EBr), and polyoxyethylene(4)mono-n-dodecyl ether (Brij-30) with a 12-carbon (C12) chain. Solubilization capacity has been quantified in terms of the molar solubilization ratio, the micelle-water partition coefficient, the first stepwise association constant between solubilizate monomer and vacant micelle, and the average number of solubilizate molecules per micelle, determined employing spectrophoto-, tensio-, and flourimetric techniques. Cationic surfactants exhibited lesser solubilization capacity than nonionics in each series of surfactants with higher efficiency in the C16 series compared to the C12 series. Increase in hydrophobicity of head groups of cationics by incorporation of ethyl or benzyl groups enhanced their solubilization capacity. The mixing effect of surfactants on mixed micelle formation and solubilization efficiency has been discussed in light of the regular solution approximation (RSA). Cationic-nonionic binary combinations showed better solubilization capacity than pure cationics, nonionics, or cationic-cationic mixtures, which, in general, showed increase with increased hydrophobicity of PAHs. Equimolar cationic-cationic-nonionic ternary surfactant systems showed lower solubilization efficiency than their binary cationic-nonionic counterparts but higher than cationic-cationic ones. In addition, use of RSA has been extended, with fair success, to predict partition coefficients of ternary surfactant systems using data of binary surfactants systems. Mixed surfactants may improve the performance of surfactant-enhanced remediation of soils and sediments by decreasing the applied surfactant level and thus remediation cost.     

Formation of 1-Butyl-3-methylimidazolium Bis(2-ethyl-1-hexyl)sulfosuccinate Stabilized Water-in-1-Butyl-3-methylimidazolium Bis(trifluoromethanesulfonyl)imide Microemulsion and the Effects of Additives

A new strategy is proposed here to formulate a bis(2-ethyl-1-hexyl)sulfosuccinate (AOT^?) stabilized water-in-ionic liquid microemulsion without any additives. Replacing the inorganic counter ion Na⁺ by the organic 1-butyl-3-methylimidazolium ([Bmim]⁺) ion greatly improves the solubility of AOT^? in hydrophobic 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([Bmim]Tf₂N) (IL) and favors the formation of water-in-IL (W/IL) microdroplets. The existence of the W/IL microdroplets has been confirmed by dynamic light scattering, Fourier transform infrared absorption spectroscopy and ultraviolet–visible absorption spectroscopy. Also, presented for the first time are the effects of salts and alcohols on the microstructure and water solubilization capacity of the ternary H₂O/[Bmim]AOT/[Bmim]Tf₂N system. For inorganic salts, larger concentrations of the salt and higher charge density of the cation result in smaller microdroplet size and weak water solubilization capacity. For 1-hexanol, a high concentration of this alcohol results in small microdroplet size but high water solubilization capacity. Analyses indicate that the salts compress the electric double layers of W/IL microemulsions, decrease the size of the microdroplets and consequently reduce the water solubilization capacity; the alcohol, however, facilitates the aggregation of AOT^?, increases the number of W/IL microdroplets, and therefore improves the water solubilization capacity of the system.     

Electrochemical, microscopic, and spectroscopic characterization of prevesicle nanostructures and vesicles on mixed cationic surfactant systems

Several experimental techniques (conductivity, zeta potential, transmission electronic microscopy, and steady-state fluorescence spectroscopy) have been used to study the formation of mixed colloidal aggregates consisting of a cationic double-chain surfactant, di-dodecyldimethylammonium bromide (di-C12DMAB), and a single-chain alkyltrimethylammonium bromide with 10 and/or 14 carbon atoms (decyltrimethylammonium bromide, C10TAB, and/or tetradecyltrimethylammonium bromide, C14TAB). Special interest has been devoted to the prevesicle domain, within which the formation of aggregated nanostructures was first reported in our laboratory. For that purpose, studies have been carried out on the very dilute region by means of conductivity experiments, confirming the existence of two critical aggregation concentrations in that concentration domain: the so-called mixed critical aggregate concentration, CAC, and the mixed critical vesicle concentration, CVC. By carrying out TEM experiments on negatively stained samples, we were surprised to find a number of aggregates without a clear aggregation pattern and with a variety of sizes and shapes at concentrations below CAC, where only monomers were expected. However, the nanoaggregates found at concentrations between CAC and CVC, also by TEM microscopy, show a clear and ordered "fingerprint"-like aggregation pattern similar to the liquid-crystalline phases reported for DNA-liposome complexes and/or DNA packed with viral capsids. Finally, at total surfactant concentrations above CVC, the aggregates were confirmed, by means of cryo-TEM micrographs and zeta potential measurements, to be essentially unilamellar spherical vesicles with a medium polydispersity and a net-averaged surface density charge of around 12 x 10(-3) C m(-2). The fluorescence emission of two probes, TNS (anionic) and PRODAN (nonionic), allows for the analysis of the micropolarity and microviscosity of the different microenvironments present in aqueous surfactant solutions where the above-mentioned vesicle and prevesicle aggregates are present.     

Effect of hydrogen bonding on the physicochemical properties and bilayer self-assembly formation of N-(2-hydroxydodecyl)-L-alanine in aqueous solution

The aggregation behavior of N-(2-hydroxydodecyl)-L-alanine (C12HAla) and N-(n-dodecyl)-L-alanine (C12Ala) was studied in aqueous buffer (pH 12) over a concentration range above their critical aggregation concentration (cac). The C12HAla amphiphile has two cacs in contrast to only one cac value for C12Ala. The micropolarity and microviscosity of the aggregates were studied by use of pyrene and 1,6-diphenyl-1,3,5-hexatriene, respectively, as fluorescent probes. Dynamic light scattering was used to measure the average hydrodynamic diameter and size distribution of the aggregates. Large size, high microviscosity, and low micropolarity values of the aggregates suggested the formation of bilayer structures in dilute solutions of C12HAla. In contrast, C12Ala was observed to form micelles. Transmission electron micrographs of dilute and moderately concentrated solutions of C12HAla revealed the existence of spherical vesicles and branching tubular structures, respectively. Comparison of the aggregation behavior of these amphiphiles to that of C12Ala and the FT-IR spectrum suggested that intermolecular hydrogen-bonding interactions between adjacent hydrocarbon chains through the -OH and -NH- groups of C12HAla are responsible for bilayer formation. The mechanism of nanotube formation was discussed. The temperature dependence of aggregate formation of the amphiphile also was investigated.     

Sphere-to-rod transitions of nonionic surfactant micelles in aqueous solution modeled by molecular dynamics simulations

Control of the size and agglomeration of micellar systems is important for pharmaceutical applications such as drug delivery. Although shape-related transitions in surfactant solutions are studied experimentally, their molecular mechanisms are still not well understood. In this study, we use coarse-grained molecular dynamics simulations to describe micellar assemblies of pentaethylene glycol monododecyl ether (C(12)E(5)) in aqueous solution at different concentrations. The obtained size and aggregation numbers of the aggregates formed are in very good agreement with the available experimental data. Importantly, increase of the concentration leads to a second critical micelle concentration where a transition to rod-like aggregates is observed. This transition is quantified in terms of shape anisotropy, together with a detailed structural analysis of the micelles as a function of aggregation number.     

Wormlike micelles in mixed surfactant systems: effect of cosolvents

We have studied the structure and rheological behavior of viscoelastic wormlike micellar solutions in the mixed nonionic surfactants poly(oxyethylene) cholesteryl ether (ChEO15)-trioxyethylene monododecyl ether (C12EO3) and anionic sodium dodecyl sulfate (SDS)-C12EO3 using a series of glycerol/water and formamide/water mixed solvents. The obtained results are compared with those reported in pure water for the corresponding mixed surfactant systems. The zero-shear viscosity first sharply increases with C12EO3 addition and then decreases; i.e., there is a viscosity maximum. The intensity (viscosity) and position (C12EO3 fraction) of this maximum shift to lower values upon an increase in the ratio of glycerol in the glycerol/water mixed solvent, while the position of the maximum changes in an opposite way with increasing formamide. In the case of the SDS/C12EO3 system, zero-shear viscosity shows a decrease with an increase of temperature, but for the ChEO15/C12EO3 system, again, the zero-shear viscosity shows a maximum if plotted as a function of temperature, its position depending on the C12EO3 mixing fraction. In the studied nonionic systems, worm micelles seem to exist at low temperatures (down to 0 degrees C) and high glycerol concentrations (up to 50 wt %), which is interesting from the viewpoint of applications such as drag reduction fluids. Rheology results are supported by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS) measurements on nonionic systems, which indicate micellar elongation upon addition of glycerol or increasing temperature and shortening upon addition of formamide. The results can be interpreted in terms of changes in the surface curvature of aggregates and lyophobicity.