Shear and extensional rheology of solutions of mixtures of poly(ethylene oxide) and anionic surfactants in ionic environments

Interactions between a high molecular weight poly(ethylene oxide) (PEO) and the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) in aqueous solutions were investigated by shear and extensional rheometry. Results for mixtures between PEO and sodium dodecyl sulfate (SDS) are also presented for comparison purposes. Addition of anionic surfactants to PEO solutions above the critical aggregation concentration (CAC), at which micellar aggregates attach to the polymer chain, results in an increase in shear viscosity due to PEO coil expansion, and a strengthening of interchain interactions. In extensional flows, these interactions result in a decrease of the critical shear rate for the onset of the characteristic extension thickening of the PEO solutions that is due to transient entanglements of polymer molecules. The relaxation times associated with these transient entanglements are not directly proportional to the shear viscosity of the solutions, but rather vary more rapidly with surfactant concentration. In the presence of an electrolyte, coil contraction results in lower shear viscosities and a decrease in the extension thickening effects at surfactant concentrations just beyond the CAC. The relaxation times associated with transient entanglement reach a minimum at the same surfactant concentration as the shear viscosity, which indicates that coil contraction is responsible for the observed effects in both types of flow. However, the increase in extensional-flow entanglement relaxation times is much more abrupt than the decrease in shear viscosity. All these results point to a greater sensitivity of extensional flows on the molecular conformation of PEO/surfactant complexes.     

Laser light scattering and isothermal titration calorimetric studies of poly(ethylene oxide) aqueous solution in presence of sodium dodecyl sulfate

The aqueous solution of poly(ethylene oxide) (PEO) in the presence of different concentrations of sodium dodecyl sulfate (SDS) was examined by laser light scattering and isothermal titration calorimetric techniques. A small fraction of PEO aggregates were found to coexist with unimeric PEO chains in dilute solution. The presence of monovalent salt does not alter the hydrodynamic properties of PEO in aqueous solution. Addition of a monovalent anionic surfactant, such as SDS, induces cooperative binding of surfactant monomers to PEO backbones at SDS concentrations ranging from 4.0 mM (critical aggregation concentration) to 16.5 mM (saturation concentration). The hydrodynamic radius of PEO unimers decreases initially and then increases with SDS concentration, resulting from the structural reorganization of the PEO/SDS complex. Beyond the saturation concentration, the hydrodynamic radii of PEO/SDS complex are independent of SDS concentration.     

The Hybrids of Polystyrene-block-Poly(ethylene Oxide) Micelles and Sodium Dodecyl Sulfate in Aqueous Solutions: Interaction with Rh Ions and Rh Nanoparticle Formation

The interaction of amphiphilic block copolymer, polystyrene-block-poly(ethylene oxide) (PS-b-PEO), with anionic surfactant, sodium dodecyl sulfate (SDS), in aqueous media has been studied by sedimentation in ultracentrifuge. Three well-defined populations of hybrid aggregates corresponding to micelles, micellar clusters, and supermicellar aggregates were detected in the PS-b-PEO/SDS aqueous solutions at various rotation rates. Parameters of all the micellar aggregates were characterized depending on the SDS loading. An increase in the SDS loading was found to result in an increase in block copolymer/surfactant micelle size and weight at the SDS concentration of 0.8x10(-3) mol/L and in a slight decrease of both parameters at critical micelle concentration and at higher concentration. This decrease was caused by incorporation of SDS molecules in block copolymer micelles followed by charging the PS core and repulsion between similar charges. Using dichlorotetrapyridine rhodium(III)chloride hexahydrate ([Rh(Py)(4)Cl(2)]Clx6H(2)O), ion exchange of surfactant counterions in the hybrid PS-b-PEO/SDS system for Rh cations was carried out, which allowed saturating the micellar structures with Rh species. Subsequent reduction of the Rh-containing hybrid solutions with NaBH(4) resulted in the formation of Rh nanoparticles with a diameter of 2-3 nm mainly located in the block copolymer micellar aggregates. Copyright 2000 Academic Press.     

Extensional viscosity of aqueous solutions of SDS and PVP measured on the rheometrics RFX

An opposed jets extensional rheometer, the Rheometrics RFX, was used to investigate the extensional flow properties of a series of solutions of polyvinylpyrrolidone (PVP) containing varying amounts of an anionic surfactant, sodium dodecylsulphate (SDS). The measurements were made in comparison with data collected for Newtonian fluids of similar viscosity to the polymeric systems of interest. The instrument was used to make measurements of the extensional viscosity as a function of extension rate, and a study of the effect of the residence time within the flow field was made. PVP has been shown to form a complex in aqueous solution with SDS. This study concentrated on the effect the addition of SDS has on the extensional rheology of semi-dilute solutions of PVP, with a molecular weight of 700 000. It was shown that increasing the amount of SDS increased the extensional thickening characteristics of solutions, as shown by a decrease in the critical extension rate for thickening. An increase in the viscosity of the solvent was shown to have an additional effect. By decreasing the distance between the opposed nozzles it was shown that a decrease in the residence time (and hence total average strain) diminished the extensional thickening character of these solutions.     

The structures of complexes between polyethylene imine and sodium dodecyl sulfate in D2O: a scattering study

The association between a highly branched polyelectrolyte with ionizable groups, polyethylene imine (PEI), and an anionic surfactant, sodium dodecyl sulfate (SDS), has been investigated at two pH values, using small-angle neutron and light scattering. The scattering data allow us to obtain a detailed picture of the association structures formed. Small-angle neutron scattering (SANS) measurements in solutions containing highly charged PEI at low pH and low SDS concentrations indicate the presence of disklike aggregates. The aggregates change to a more complex three-dimensional structure with increasing surfactant concentration. One pronounced feature in the scattering curves is the presence of a Bragg-like peak at high q-values observed at a surfactant concentration of 4.2 mM and above. This scattering feature is attributed to the formation of a common well-ordered PEI/SDS structure, in analogue to what has been reported for other polyelectrolyte-surfactant systems. Precipitation occurred at the charge neutralization point, and X-ray diffraction measurements on the precipitate confirmed the existence of an ordered structure within the PEI/SDS aggregates, which was identified as a lamellar internal organization. Polyethylene imine has a low charge density in alkaline solutions. At pH 10.1 and under conditions where the surfactant was contrast matched, the SANS scattering curves showed only small changes with increasing surfactant concentration. This suggests that the polymer acts as a template onto which the surfactant molecules aggregate. Data from both static light scattering and SANS recorded under conditions where SDS and to a lower degree PEI contribute to the scattering were found to be consistent with a structure of stacked elliptic bilayers. These structures increased in size and became more compact as the surfactant concentration was increased up to the charge neutralization point.     

Studies on the Interaction of Surfactants with Cationic Dye by Absorption Spectroscopy

The interaction of methyl violet, a cationic dye, with various surfactants, viz. anionic (SDS), nonionic (Triton X-100), and cationic (CTAB), has been investigated spectrophotometrically in submicellar and micellar concentration range. While in the submicellar concentration region of SDS the higher aggregates of the dye are found, in the micellar concentration region the monomer of the dye predominates. With nonionic surfactant the dye is solubilized primarily as the monomer. CTAB produces no perturbation to the visible spectra of the dye. In the presence of strong electrolytes such as NaNO(3) and NaCl the dye aggregates are formed at a much lower SDS concentrations. Copyright 2000 Academic Press.     

Structural and dynamical properties of ribbonlike self-assemblies of a fluorinated cationic surfactant

The structural and dynamic properties of low ionic strength micellar solutions of the cationic surfactant perfluorooctylbutane trimethylammonium bromide have been investigated by cryo-TEM, small-angle neutron scattering, small-angle X-ray scattering, T-jump and rheological experiments. The surfactant molecules self-assemble into narrow ribbons with average dimensions on the order of 4 nm x 3 nm, either under salt-free conditions or in the presence of up to 30 mM KBr or NaF. Cryo-TEM also reveals in the salt-free systems the presence of networks of multiconnected micelles. Rheological experiments showed that these surfactant systems exhibit a strong shear-thickening effect even in the presence of up to 30 mM KBr. The T-jump response of the micellar solutions was found to be multiexponential. This observation rules out the presence of only linear micelles with an exponential length distribution and suggests more complex topologies of the micellar aggregates. The relaxation time associated with the predominant process in the T-jump relaxation is strongly correlated to the critical shear rate beyond which shear thickening occurs, thus indicating that this critical shear rate is controlled by the micellar kinetics.     

Test of Hofmeister-like series of anionic headgroups: clouding and micellar growth

Phenomenon of clouding in charged micellar solutions is a fairly recent addition to conventional phenomenon shown by aqueous nonionic micelles. In this paper, we have tested a Hofmeister-like ordering of charged headgroups in the context of cloud point (CP) and micellar growth. For this purpose, we have used various combinations of surfactant (sodium dodecyl sulfate, SDS; sodium dodecylbenzene sulfonate, SDBS; sodium salts of α-sulfonato myristic acid methyl ester, MES; and α-sulfonato palmitic acid methyl ester, PES) and tetra-n-butylammonium bromide (TBAB). Different surfactant concentrations and TBAB concentrations are used and CP measurements have been performed. CP values were found in the order SDBS?<?SDS?<?PES?<?MES for the same concentration of surfactant and TBAB. This order has been discussed in the light of water affinities of interacting ionic species (i.e., surfactant headgroup and TBA⁺ counterion). The ordering was found similar for the case of micellar growth studied by dynamic light scattering (DLS). A bimodal distribution of aggregate size was found that transforms to giant aggregates at CP. The micelles of roughly 10-nm size convert to aggregates of 1 μm. The study has a few novelties: (1) headgroup dependence of CP, (2) micellar growth on heating, and (3) confirmation of Hofmeister-like series of headgroup.     

Effects of electrolyte concentration and counterion valence on the microstructural flow regimes in dilute cetyltrimethylammonium tosylate micellar solutions

The shear thickening behavior and the transition to shear thinning are examined in dilute cetyltrimethylammonium tosylate (CTAT) micellar solutions as a function of surfactant concentration and ionic strength using electrolytes with different counterion valence. Newtonian behavior at low shear rates, followed by shear thickening and shear thinning at higher shear rates, are observed at low and intermediate surfactant and electrolyte concentrations. Shear thickening diminishes with increasing surfactant concentration and ionic strength. At higher surfactant or electrolyte concentration, only a Newtonian region followed by shear thinning is detected. A generalized flow diagram indicates two controlling regimes: one in which electrostatic screening dominates and induces micellar growth, and another, at higher electrolyte and surfactant concentrations, where chemical equilibrium among electrolyte and surfactant counterions controls the rheological behavior by modifying micellar breaking and reforming. Analysis of the shear thickening behavior reveals that not only a critical shear rate is required for shear thickening, but also a critical deformation, which appears to be unique for all systems examined, within experimental error. Moreover, a superposition of the critical shear rate for shear thickening with surfactant and electrolyte concentration is reported.     

Swelling of poly(ethylene oxide) gel in aqueous solutions of sodium dodecyl sulfate with added sodium chloride

The swelling behavior of poly(ethylene oxide) (PEO) gels in aqueous solutions of sodium dodecyl sulfate (SDS) with and without NaCl was investigated. In the absence of NaCl, PEO gels with different degrees of cross-linking began to swell from a concentration lower than the critical micelle concentration (cmc) of SDS, then showed sigmoidal enhancements of swelling in a higher SDS concentration region until the degrees of swelling reached maximum values. The SDS concentration at which the swelling began to appear was in reasonable agreement with the critical aggregation concentration (cac) value reported for the aqueous PEO system. For the cases where NaCl was present, the swelling behavior of PEO gel was different from that when NaCl was absent in the following way. The concentrations where the swelling begins to appear, and hence those where the degree of swelling rises steeply, decreased with an increase in NaCl concentration. The ultimate degrees of swelling at higher concentration regions also decreased with an increase in the NaCl concentration. The lowering of the SDS concentrations at which the PEO gel began to swell is in line with the decreases in the cmc of SDS solutions containing NaCl and also with the decreases in the cac of PEO solution. Electronic Publication     

Dependence of the size of a protein-SDS complex on detergent and Na+ concentrations

Sodium dodecyl sulfate (SDS) micelles provide ideal mimetic media for high-resolution NMR studies of membrane proteins and proteins or peptides interacting with micellar aggregates. (15)N NMR relaxation of the backbone amides of a protein-SDS complex has been measured under different experimental conditions. The rotational diffusion time of this complex has been found highly sensitive to detergent and NaCl concentrations. A comparison with calculated rotational diffusion times of protein-free SDS micelles under the same conditions suggests that the size of both aggregates must follow a similar functional dependence on detergent/NaCl concentration.     

Chlorpromazine and sodium dodecyl sulfate mixed micelles investigated by small angle X-ray scattering

Small-angle X-ray scattering (SAXS) studies are reported on the interaction of chlorpromazine (CPZ) with micelles of anionic surfactant sodium dodecyl sulfate (SDS). Isotropic solutions of SDS (40 and 100 mM) at pH 4.0, 7.0, and 9.0 in the absence and presence of CPZ (2-25 mM) were investigated at the National Laboratory of Synchrotron Light (LNLS, Campinas, Brazil). The data were analyzed through the modeling of the micellar form factor and interference function. The results evidence a micellar shape transformation from prolate ellipsoid to cylinder accompanied by micellar growth and surface charge screening as the molar ratio CPZ : SDS increases in the complex. Small ellipsoids with axial ratio nu=1.5+/-0.1 at 40 mM SDS grow and reassemble into cylinder-like aggregates upon 5 mM drug incorporation (1 CPZ : 8 SDS monomers) with a decrease of the micelle surface charge. At 10 mM CPZ : 40 mM SDS cylindrical micelles are totally screened with an axial ratio nu approximately 2.5. The data also indicate the presence of small prolate ellipsoids (nu=1.7+/-0.1) in solutions of 100 mM SDS (no drug) and micellar growth (nu approximately 2.0 and 4.0) when 10 and 25 mM CPZ are added to the system. In the latter case, the aggregate is also better represented by a cylinder-like form. Therefore, our results demonstrate that the axial ratio and shape evolution of the surfactant : phenothiazine complex are both SDS concentration and drug : SDS molar ratio dependent. The drug location close to the SDS polar headgroup region without disrupting in a significant way both the paraffinic hydrophobic core and the polar shell thickness is inferred. SAXS data made it possible to obtain the shapes and dimensions of CPZ/SDS aggregates.     

Nonequilibrium features of the association between poly(vinylamine) and sodium dodecyl sulfate: the validity of the colloid dispersion concept

The effect of different mixing protocols on the bulk and surface properties of the aqueous mixtures of linear poly(vinylamine) (PVAm) and sodium dodecyl sulfate (SDS) has been investigated using pH, electrophoretic mobility, dynamic light scattering, coagulation kinetics, and surface tension measurements. For the preparation of the solutions, two kinds of mixing protocols were applied. The so-called "stop flow mixing" enables a very rapid mixing whereas in the case of "gentle mixing" the mixing of the components is less efficient. At high surfactant concentrations a kinetically stable colloid dispersion of the PVAm/SDS particles is formed via the application of the stop flow mixing method. The mixing protocols have a significant effect on the bulk properties of the PVAm/SDS system, in particular, at the low pH range and at large PVAm concentrations. The effect of mixing can be qualitatively understood in terms of the enhanced local rate of coagulation of the PVAm/SDS complexes as well as of the appearance of polyelectrolyte/surfactant aggregates via the application of a less efficient mixing. The study also reveals that the applied methods of solution preparation do not have a major impact on the bound amount of the surfactant as well as on the surface tension isotherms of the system. This latter finding is attributed to the hindered adsorption of the large polyelectrolyte/surfactant aggregates at the air/water interface.     

Influence of a surfactant and electrolytes on adsorbed polymer layers

Solvent relaxation NMR and small-angle neutron scattering have been used to characterize adsorbed poly(ethylene oxide) (PEO) layers on silica at a range of surfactant and electrolyte concentrations. Below the critical aggregation concentration (cac), the results suggest that sodium dodecyl sulfate (SDS) interacts relatively weakly, perhaps analogously to a simple salt reducing the solvency of PEO. This is evidenced by a decrease in the adsorbed layer thickness combined with an increase in the bound fraction, although the total adsorbed amount is not greatly affected. The layer thickness goes through a minimum at the cac, after which further SDS addition results in the formation of PEO/SDS aggregates that repel each other and, hence, tend to desorb. The adsorbed amount therefore decreases, from 0.7 mg m(-2) initially to 0.2 mg m(-2) with 32 mM SDS. The aggregates that remain adsorbed also repel, and hence, there is an increase in the layer thickness and the persistence length, while the bound fraction is reduced. In comparison, the effects of electrolyte at the ionic strength studied are relatively minimal. There is, however, evidence that the repulsions between adsorbed PEO/SDS aggregates are partially screened, allowing them to approach each other more readily. This leads to a contraction of the adsorbed layer when the SDS concentration is sufficiently high.     

DMABN在表面活性剂胶束水溶液中的荧光性质

研究了对二甲氨基苯甲腈(DMABN)在各种胶束水溶液中的荧光光谱性质, 发现不同胶束栅栏层区域的不同性质影响了探针的分子内扭转电荷转移(TICT)特性. 对离子型胶束, 头基电场是主要影响因素, 促进了DMABN分子TICT态的形成, 反离子解离度琢越大, 胶束溶液中的Ia/Ib越强. 在非离子表面活性剂胶束中, 聚氧乙烯链环外壳包裹的大量水使其氢键影响明显, 而很短的聚氧乙烯链还可能带来端基氢的氢键作用. 从DMABN的光物理特性看, 欲将胶束作为分散载体利用其TICT态特性, 选择反离子解离度较大的阴离子胶束(例如SDS或SDSO)较好.     

The Effects of Salts and Ionic Surfactants on the Micellar Structure of Tri‐Block Copolymer PEO‐PPO‐PEO in Aqueous Solution

The micelles of two poly(ethylene oxide)‐poly(propylene oxide)‐poly(ethylene oxide) (PEO‐PPO‐PEO) block copolymers, P123 and F127 (same mol wt of PPO but different % PEO) in aqueous solution in the absence and presence of salts as well as ionic surfactants were mainly examined by dynamic light scattering (DLS). The study is further supported by cloud point and viscosity measurements. The change in cloud point (CP), as well as the size of micelles in aqueous solution in presence of salts obeys the Hofmeister lyotropic series. Addition of both cationic cetylpyridinium chloride (CPC) and anionic sodium dodecylsulfate (SDS) surfactants in the aqueous solution of P123 show initial decrease of micellar size from 20 nm to nearly 7 nm and then increasing with a double relaxation mode, further in the presence of NaCl this double relaxation mode vanishes. The effect of surfactant on F127, which has much bigger hydrophilic part is different than P123 and have no double relaxation. The relaxation time distributions is obtained using the Laplace inversion routine REPES. Two relaxation modes for P123 are explained on the bases of Pluronic rich mixed micelles containing ionic surfactants and the other smaller, predominantly surfactant rich micelles domains.     

The Viscous Properties of Anionic/Cationic and Cationic/Nonionic Mixed Surfactant Systems

The behavior of mixed cationic/anionic and cationic/nonionic surfactants solutions have been studied by viscosimetry. The systems studied were sodium dodecyl sulfate (SDS)/cetyltrimethylammonium bromide (CTAB) and CTAB/Brij (polyoxyethylene lauryl ether, n = 10 and 23) in aqueous and sodium chloride solutions. The relative viscosity of single nonionic surfactant solutions is larger than that of SDS or CTAB solutions. It increases with the number of ethylene oxide groups. In the mixed systems, viscosity deviates from ideal behavior. The deviation results from electrostatic interactions. The surfactant mixture composition affects the self-assembled microstructure and rheology. A new mixed system that forms clear micellar solution above CMC was detected. In CTAB/Brij systems, the experimental data also deviate from ideal behavior due to mixed micelle formation and electroviscous effect. This effect is less pronounced than that of SDS/CTAB system and could be suppressed by adding an electrolyte (NaCl).     

Physicochemical studies on hydrophobic PEO‐PPO‐PEO triblock copolymer micelles in SDS micellar environment

The shape, size, aggregation, hydration, and correlation times of water insoluble PEO‐PPO‐PEO triblock copolymer micelles with sodium dodecylsulfate (SDS) micelles were investigated using transport studies and dynamic light scattering technique. From the conductance of micellar solutions of the polymer in 25 mM SDS and 5 mM NaCl, the hydration of polymer micelles were determined using the principle of obstruction of electrolyte migration by the polymer. The asymmetry of the micellar particles of polymer and polymer‐SDS mixed micellar systems in 5 mM NaCl and their average axial ratios were calculated using intrinsic viscosity and hydration data obeying Simha–Einstein equation. Hydration number and micellar sizes were variable with temperature. The shape of the polymer micelles has been ellipsoidal rather than spherical. The micellar volume, hydrodynamic radius, radius of gyration, diffusional coefficients as well as translational, rotational and effective correlation times have been calculated from the absolute values of the axes. The partial molal volume of polymer micelles has also been determined and its comparison with the molar volume of pure polymer suggested a volume contraction due to immobilization of the water phase by the hydrophilic head groups of the polymer. The thermodynamic activation parameters for viscous flow favor a more ordered water structure around polymer micelles at higher temperatures. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2410–2420, 2007     

Effect of SDS on the self-assembly behavior of the PEO-PPO-PEO triblock copolymer (EO)20(PO)70(EO)20

The mixed micellar system comprising the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide)-based triblock copolymer (EO)(20)(PO)(70)(EO)(20) (P123) and the anionic surfactant sodium dodecyl sulfate (SDS) has been investigated in aqueous media by small-angle neutron scattering (SANS) and viscosity measurements. The aggregation number of the copolymer in the micelles decreases upon addition of SDS, but a simultaneous enhancement in the degree of micellar hydration leads to a significant increase in the micellar volume fraction at a fixed copolymer concentration. This enhancement in the micellar hydration leads to a marked increase in the stability of the micellar gel phase until it is destroyed at very high SDS concentration. Mixed micellar systems with low and intermediate SDS concentrations form the micellar gel phase in much wider temperature and copolymer concentration ranges than the pure copolymer micellar solution. A comparison of the observed results with those for the copolymers (EO)(26)(PO)(40)(EO)(26) (P85) and (EO)(99)(PO)(70)(EO)(99) (F127) suggests that the composition of the copolymers plays a significant role in determining the influence of SDS on the gelation characteristics of the aqueous copolymer solutions. Copolymers with high PO/EO ratios show an enhancement in the stability of the gel phase, whereas copolymers with low PO/EO ratios show a deterioration of the same in the presence of SDS.     

Interactions between chitosan and SDS at a low-charged silica substrate compared to interactions in the bulk--the effect of ionic strength

The effect of ionic strength on association between the cationic polysaccharide chitosan and the anionic surfactant sodium dodecyl sulfate, SDS, has been studied in bulk solution and at the solid/liquid interface. Bulk association was probed by turbidity, electrophoretic mobility, and surface tension measurements. The critical aggregation concentration, cac, and the saturation binding of surfactants were estimated from surface tension data. The number of associated SDS molecules per chitosan segment exceeded one at both salt concentrations. As a result, a net charge reversal of the polymer-surfactant complexes was observed, between 1.0 and 1.5 mM SDS, independent of ionic strength. Phase separation occurs in the SDS concentration region where low charge density complexes form, whereas at high surfactant concentrations (up to several multiples of cmc SDS) soluble aggregates are formed. Ellipsometry and QCM-D were employed to follow adsorption of chitosan onto low-charged silica substrates, and the interactions between SDS and preadsorbed chitosan layers. A thin (0.5 nm) and rigid chitosan layer was formed when adsorbed from a 0.1 mM NaNO3 solution, whereas thicker (2 nm) chitosan layers with higher dissipation/unit mass were formed from solutions at and above 30 mM NaNO3. The fraction of solvent in the chitosan layers was high independent of the layer thickness and rigidity and ionic strength. In 30 mM NaNO3 solution, addition of SDS induced a collapse at low concentrations, while at higher SDS concentrations the viscoelastic character of the layer was recovered. Maximum adsorbed mass (chitosan + SDS) was reached at 0.8 times the cmc of SDS, after which surfactant-induced polymer desorption occurred. In 0.1 mM NaNO3, the initial collapse was negligible and further addition of surfactant lead to the formation of a nonrigid, viscoelastic polymer layer until desorption began above a surfactant concentration of 0.4 times the cmc of SDS.