Addition Of Surfactant Sodium Dodecyl Sulfate Research Articles

Stepwise Unfolding of Bovine and Human Serum Albumin by an Anionic Surfactant: An Investigation Using the Proton Transfer Probe Norharmane

Interactions of the anionic surfactant sodium dodecyl sulfate (SDS) with the transport proteins bovine serum albumin (BSA) and human serum albumin (HSA) have been divulged using an external photoinduced proton transfer probe, norharmane (NHM). Steady-state fluorometry, time-resolved measurements, micropolarity analysis, circular dichroism (CD), and isothermal titration calorimetry (ITC) have been exploited for the study. With the gradual addition of SDS to the probe-bound proteins, the fluorometric responses of the different prototropic species of NHM exhibit an opposite pattern as to that observed while NHM binds to the proteins. The study reveals a sequential unfolding of the serum proteins with the gradual addition of SDS. ITC measures the heat changes associated with each step of the unfolding. ITC experiments, carried out at two different pH's, elucidate the nature of interaction between SDS and the two serum proteins. At a very high concentration of SDS, the external probe (NHM) is found to be dislodged from the protein environments to bind to the SDS micellar medium.

Effects of sodium dodecyl sulfate on the electrochemical behavior of supercapacitor electrode MnO2

Supercapacitor electrode material MnO2 was prepared by liquid co-precipitation with different concentration of anionic surfactant sodium dodecyl sulfate (SDS). As evidenced by X-ray diffraction, the obtained MnO2 are all typical amorphous α-MnO2 with poor crystallinity. Scanning electron microscopy reveals that the dispersity of MnO2 initially get better and then worse with the increase of SDS, and the particle sizes first become smaller then larger as well. It is worthwhile noting that the morphology of MnO2 tested by transmission electron microscopy undergoes a changeable process: fibrous, pine needle like, cotton like, round bubble like, flocculent, and nervous tissue like as SDS increases. Through cyclic voltammetry and galvanostatic charge/discharge tests, SDS addition amount 0.2 g (0.017 mol L−1) is found to be the optimal effect value, and the as-prepared Mn-0.2 obtains the highest specific capacitance (Csp) of 154.5 F g−1 at a current density of 500 mA g−1. Compared with the sample Mn-0 synthesized without SDS, the Csp increases by about 50 % (±5 %), which can be attributed to its largest Brunauer–Emmett–Teller–specific surface area of 255.9 m2 g−1, best particle dispersity, and smallest particle size of approximately 50–80 nm. Meanwhile, the rate capability and cycle stability of Mn-0.2 also improves obviously, and the equivalent series resistance decreases a lot, only 0.120 Ω.

Tuning the Probe Location on Zwitterionic Micellar System with Variation of pH and Addition of Surfactants with Different Alkyl Chains: Solvent and Rotational Relaxation Studies

In this manuscript, we have modulated the location of an anionic probe, Coumarin-343 (C-343) in a zwitterionic (N-hexadecyl-N,N-dimethylammonio-1-propanesulfonate (SB-16)) micellar system by three different approaches. The effect of addition of the surfactant sodium dodecyl sulfate (SDS) and the room temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium octylsulfate (EmimOs) and N,N-dimethylethanol hexanoate (DAH), to the micellar solution has been studied. The effect of pH variation has been studied as well using solvent and rotational measurements. Migration of the anionic probe, C-343, from the palisade layer of SB-16 micelle to the bulk water has been observed to varying extents with the addition of SDS and EmimOs. The effect is much more pronounced in the presence of SDS and can be ascribed to the presence of the long alkyl (dodecyl) chain on SDS which can easily orient itself and fuse inside the SB-16 micelle and facilitate the observed migration of the probe molecule. This phenomenon is confirmed by faster solvation and rotational relaxation of the investigated probe molecule. The analogous fusion process is difficult in case of EmimOs and DAH because of their comparatively smaller alkyl (octyl and hexanoate) chain. However, the direction of C-343 migration is reversed with the decrease of pH of the SB-16 micellar medium. An increase in the average solvation and rotational relaxation time of the probe in acidic medium has been observed. Since experimental conditions are maintained such that the probe molecules and the zwitterionic SB-16 micelles remain oppositely charged, the observed results can be attributed to the increased electrostatic interaction (attractive) between them. Temperature dependent study also supports this finding.

Synthesis of molybdenum nanoparticle by in situ γ-radiation

This paper reports the synthesis of various types of molybdenum nanoparticles using in-situ minuscule amount of radioactivity. The radioisotope 99Mo was introduced into the solution of (i) 10−5M ammonium molybdate and (ii) mixture of 10−5M ammonium molybdate and anionic surfactant sodiumdodecyl sulphate (SDS). The molybdate ions were changed to nanoparticles due to radiolysis initiated by γ-irradiation in both the cases. The transmission electron microscopic images showed 4–15nm size nanoparticles with spherical shape in ammonium molybdate solution. However, the aggregation of nanoparticles could not be avoided in this case. The addition of SDS to the solution helped to obtain 10–60nm size of spherical molybdenum nanoparticle and 2–10nm wire like molybdenum nanoparticle. Interpretation of spectral data advocates that the molybdenum nanoparticles might be in MoO3 form.

Surfactant-Induced Marangoni Eddies Alter the Coffee-Rings of Evaporating Colloidal Drops

The influence of the small ionic surfactant sodium dodecyl sulfate (SDS) on the evaporation of drying colloidal droplets is quantitatively investigated. The addition of SDS leads to a significantly more uniform deposition of colloidal particles after evaporation (i.e., the so-called "coffee-ring effect" is dramatically altered). We understand this phenomenon in the context of circulating radial Marangoni flows induced by the variation of SDS concentration along the air-water interface. Video microscopy permits the direct visualization of the colloidal particles involved in these flows, revealing a surprisingly stable "Marangoni eddy" that prevents particle deposition at the drop perimeter.

Modulating self-assembly of a nanotape-forming peptideamphiphile with an oppositely charged surfactant

A peptide amphiphile (PA) C16-KTTKS, containing a pentapeptide headgroup based on a sequence from procollagen I attached to a hexadecyl lipid chain, self-assembles into extended nanotapes in aqueous solution. The tapes are based on bilayer structures, with a 5.2 nm spacing. Here, we investigate the effect of addition of the oppositely charged anionic surfactant sodium dodecyl sulfate (SDS) viaAFM, electron microscopic methods, small-angle X-ray scattering and X-ray diffraction among other methods. We show that addition of SDS leads to a transition from tapes to fibrils, via intermediate states that include twisted ribbons. Addition of SDS is also shown to enhance the development of remarkable lateral “stripes” on the nanostructures, which have a 4 nm periodicity. This is ascribed to counterion condensation. The transition in the nanostructure leads to changes in macroscopic properties, in particular a transition from sol to gel is noted on increasing SDS (with a further re-entrant transition to sol on further increase of SDS concentration). Formation of a gel may be useful in applications of this PA in skincare applications and we show that this can be controlled via development of a network of fine stranded fibrils.

Production of palladium nanoparticles supported on multiwalled carbon nanotubes by gamma irradiation

Palladium nanoparticles were produced and supported on multiwalled carbon nanotubes (MWCNT) by gamma irradiation. A solution with a specific ratio of 2:1 of water–isopropanol was prepared and mixed with palladium chloride and the surfactant sodium dodecyl sulfate (SDS). The gamma radiolysis of water ultimately produces Pd metallic particles that serve as nucleation seeds. Isopropanol is used as an ion scavenger to balance the reaction, and the coalescence of the metal nanoparticles was controlled by the addition of SDS as a stabilizer. The size and distribution of nanoparticles on the carbon nanotubes (CNT) were studied at different surfactant concentrations and radiation doses. SEM, STEM and XPS were used for morphological, chemical and structural characterization of the nanostructure. Nanoparticles obtained for doses between 10 and 40 kGy, ranged in size 5–30 nm. The smaller nanoparticles were obtained at the higher doses and vice versa. Histograms of particle size distributions at different doses are presented.

Equilibrium Studies on the System Water + Hydrogen Peroxide + Urea + Carbon Dioxide

To develop a new method for separating the residual liquid of peroxide urea production by the formation of gas hydrate, the equilibrium of the system water + hydrogen peroxide + urea + carbon dioxide was studied under the conditions of P = (1.2 to 1.9) MPa and T = (273.15 to 303.15) K. The equilibrium pressure and temperature of gas hydrate formation were investigated at the different concentrations of hydrogen peroxide and urea with the anionic surfactant sodium dodecyl sulfate (SDS) and the sodium dodecyl benzene sulfonate (SDBS) in the system and without either. It was found that the equilibrium pressure of gas hydrate formation increased with the increase of temperature and the mass fraction of hydrogen peroxide and urea. The addition of anionic surfactant SDBS and SDS lowered the equilibrium pressure of the gas hydrate formed. The equilibrium pressure of the gas hydrate formed was calculated by Chen−Guo thermodynamic model, and the calculated values were in accord with the experimental results.

Viscosification in Polymer−Surfactant Mixtures at Low Temperatures

Interactions between the anionic surfactant sodium dodecyl sulfate (SDS) and hydroxyethylcellulose (HEC) or its hydrophobically modified analogue (HM-HEC) have been studied over an extended temperature region with the aid of turbidimetry, small-angle neutron scattering (SANS), and shear viscosimetry. Anomalous viscosity enhancements were observed for semidilute HEC/SDS and HM-HEC/SDS solutions at high SDS concentrations at temperatures far below the Krafft point for aqueous solutions of SDS. From the Arrhenius-Frenkel-Eyring (AFE) plots of the temperature dependence of the zero-shear viscosity, the activation energy of chain disengagement (DeltaE(vis)) was found to be on the order of 40 kJ mol(-1) for the HEC/SDS mixtures, whereas for the HM-HEC/SDS system, much higher values of DeltaE(vis) (up to 141 kJ mol(-1)) were reported, and the activation energy increased with an increasing level of SDS addition. Break points in the AFE plots were observed for both the HEC/SDS and HM-HEC/SDS systems at low temperatures and high SDS concentrations. Time evolutions of both the turbidity and the shear viscosity were monitored after quenching of the temperature from 25 to 1 degrees C. The turbidity results revealed in general a less pronounced transition for the HEC/SDS and HM-HEC/SDS systems than for the corresponding polymer-free SDS/water solutions. In the course of time, a significant viscosity enhancement was found for the HEC/SDS system at high levels of SDS addition, and a much stronger viscosification was observed for the HM-HEC/SDS system at the highest surfactant concentration. The overall results suggest that hydrated SDS aggregates act as cross-linkers of the network and generate the substantial viscosification of the systems at low temperature and high levels of SDS addition. For the HM-HEC/SDS system, further strengthening of the network occurs because of the contribution from hydrophobic interactions. The SANS data on HEC/SDS mixtures reveal that some structural reorganization takes place at low temperatures in the presence of high SDS concentrations, and this is ascribed to enhanced polymer-SDS interactions and the formation of clusters that strengthened the cross-links of the network.

Surface Adsorption and Phase Separation of Oppositely Charged Polyion−Surfactant Ion Complexes: 3. Effects of Polyion Hydrophobicity

The adsorption to hydrophilic silica surfaces in relation to the bulk phase behavior was investigated by in situ null ellipsometry and bulk turbidity measurements for four cationic copolymers of varying hydrophobicity in mixtures with anionic surfactant sodium dodecylsulfate (SDS). The purpose was to reveal the effect of polyion hydrophobicity on the association with surfactant at surfaces and in the bulk. All polyelectrolytes contained 20 wt % cationic units and had similar molecular weights. An increase in surfactant concentration by the stepwise addition of SDS to a dilute polyelectrolyte solution led to an increase in both the adsorbed amount and bulk turbidity, starting at a defined SDS concentration, as a result of the formation of insoluble polyion-surfactant ion complexes. At some higher SDS concentration, the formed aggregates started to redissolve gradually in the bulk and desorb from the surface because of the overcharging of the complexes. The SDS concentration at which the maxima in adsorption and turbidity occurred increased with decreasing polyion hydrophobicity; the more hydrophobic polyions bound excess SDS more readily, and the aggregates therefore redissolved at a lower SDS concentration. The adsorption from polyelectrolyte-SDS solutions, premixed at SDS concentrations above the adsorption maximum, which occurred on diluting the solution by "rinsing" the ellipsometer cuvette with 1 mM NaCl, was also investigated. On dilution, both the turbidity and the adsorbed amount increased as the excess surfactant in the polyion-surfactant ion complexes progressively decreased. More efficient deposition was achieved if the initial SDS concentration was close to the adsorption maximum. The latter situation could be achieved either by adjusting the SDS concentration or, at a fixed SDS concentration, by choosing a polyion with the appropriate hydrophobicity.

Tuning the assembly of amphiphilic block copolymers through instabilities of solvent/water interfaces in the presence of aqueous surfactants

The influence of the water-soluble surfactant sodium dodecyl sulfate (SDS) on the self-assembly of amphiphilic block copolymers through hydrodynamic instabilities of organic solvent/water interfaces was studied. Micropipette aspiration measurements performed on evaporating chloroform droplets containing polystyrene-b-poly(ethylene oxide) (PS-PEO) revealed that interfacial instabilities were correlated to an approach of the organic/water interfacial tension to zero. The addition of SDS to the aqueous phase lowered the interfacial tension, thereby facilitating the onset of instability at lower concentrations of PS-PEO within the droplets. Further, increased amounts of SDS led to qualitatively different mechanisms of interfacial instability and correspondingly different morphologies of the resulting copolymer/surfactant assemblies. Similar, though less pronounced, effects were obtained using poly(vinyl alcohol) (PVOH) as a water-soluble surfactant, reflecting its more weakly concentration-dependent surface activity. These results enabled a single PS-PEO or polybutadiene-PEO block copolymer of fixed composition to be processed into aggregates that could be easily tuned from multi-vesicular particles to wormlike micelles and to spherical micelles.

Effects of anionic surfactant SDS on the photophysical properties of two fluorescent molecular sensors

Two fluorescent molecular sensors CS1 and CS2 were designed and synthesized to probe the aggregate behavior of anionic surfactant SDS. CS1 was based on the photo-induced electron transfer (PET) mechanism, while CS2 was founded on the intramolecular charge transfer (ICT) mechanism. The photophysical properties of CS1–2 in anionic surfactant sodium dodecyl sulfate (SDS) solution were studied by fluorescence and UV–vis methods. The experimental results show that significant absorption and emission spectral responses of CS1 were observed with the addition of SDS: the absorbance and fluorescence intensity decreased first and then increased. The plot of fluorescence intensity of CS1 versus SDS concentration showed two break points, which might be ascribed to the critical micellar concentration (cmc) and the formation of premicelle (cac) aggregate, respectively. But the solution’s color of CS2 changed from yellow to red with increasing SDS concentrations. The large red-shift in both absorption (50 nm) and emission (55 nm) spectra of CS2 was resulted from the protonation of the electron accepting moiety (N C nitrogen), which enhanced the “push–pull” interaction of the ICT fluorophore. This was facilitated by the increase of local H + concentration around SDS premicelle and micelle. As a consequence, p K a values of CS1 and CS2 were elevated in SDS micelle.

Interaction behaviors in aqueous solutions of negatively and positively charged hydrophobically modified hydroxyethylcellulose in the presence of an anionic surfactant

In this study, turbidity, rheology, dynamic light scattering (DLS), and rheo-small angle light scattering (rheo-SALS) measurements have been carried out on aqueous semidilute solutions of anionic and cationic hydrophobically modified hydroxyethylcellulose (HM-HEC(−) and HM-HEC(+)) (with the same degrees of charge and hydrophobic modification) and their uncharged (HM-HEC) and unmodified (HEC) analogues in the presence of the anionic surfactant sodium dodecyl sulfate (SDS). The effect of various surfactant concentrations on the association behavior has been examined. Addition of low or moderate levels of the oppositely charged surfactant to the solutions of HM-HEC(+) leads to the formation of polyelectrolyte complexes and associative phase-separation behavior, whereas at surfactant concentrations above the charge neutrality point, a single phase emerges. At high SDS concentrations the hydrophobic interactions are reduced and this leads to lower viscosity values as well as a faster relaxation process from DLS. For the polymer (HM-HEC(−)) with charges of the same sign as the surfactant, complete miscibility was found at all solution conditions. In this case, a maximum strength of the network was observed at a surfactant concentration of approximately 5 mm, where mixed polymer–surfactant micelles are formed. The scattered intensity monitored from rheo-SALS experiments for the HM-HEC(−)/SDS and HM-HEC(+)/SDS solutions revealed significant structural changes under the influence of high shear rates. The hydrophobically modified HM-HEC polymer precipitates in water but it becomes soluble at higher levels of SDS addition. As the surfactant concentration is increased, more hydrophobic moieties are gradually deactivated and lower viscosity values are registered. At high levels of surfactant addition, the hydrophobic associations are disrupted and the electrostatic interactions are screened, leading to virtually the same behavior of all the investigated polymers.

Spatio-Temporal Perturbation of the Dynamics of the Ferroin Catalyzed Belousov−Zhabotinsky Reaction in a Batch Reactor Caused by Sodium Dodecyl Sulfate Micelles

The effects of the anionic surfactant sodium dodecyl sulfate (SDS) on the spatio-temporal and temporal dynamics of the ferroin-catalyzed Belousov-Zhabotinsky (BZ) reaction have been studied over a wide surfactant concentration range. For the first time, investigations were performed also for unstirred systems. The presence of SDS in the reaction mixture influences the oscillatory parameters to an extent that significantly depends on the surfactant concentration. The trend of the wave speed v upon the increasing amount of SDS was found to have a maximum at [SDS] = 0.075 mol dm (-3) ( v = 0.071 mm s (-1)), after which the speed decreased to 0.043 mm s (-1) at [SDS] = 0.5 mol dm (-3), which is below the value found in the absence of the surfactant ( v = 0.055 mm s (-1)). The response of the oscillatory BZ system to the addition of SDS has been ascribed to two different causes: (a) the peculiar capability of the organized surfactant assemblies to affect the reactivity by selectively sequestering some key reacting species and (b) the modifications induced by SDS on the physical properties of the medium. These hypotheses have been corroborated by performing spectrophotometric investigations on the stirred BZ system. Complementary viscosity measurements gave useful hints for the clarification of the surfactant role.

Tuning the Optical Properties of a Water-Soluble Cationic Poly(p-Phenylenevinylene): Surfactant Complexation with a Conjugated Polyelectrolyte

In this work, we investigate the emission and absorbance properties of the novel water-soluble cationic conjugated polymer poly{2,5-bis[3-(N,N,N-triethylammonium bromide)-1-oxapropyl]-1,4-phenylenevinylene}, denoted here as P2, in the presence of varying amounts of the anionic surfactant sodium dodecylsulfate (SDS). We show that the absolute photoluminescence quantum efficiency (PLQE), the absorption wavelength, and the emission wavelength of an aqueous solution of P2 can be adjusted according to the surfactant/polymer ratio in aqueous solution. In particular, we show that the addition of SDS to P2 increases the polyelectrolyte's PLQE to approximately 40%. An observed red shift in the emission spectra upon addition of the surfactant is attributed to the reduction in electrostatic repulsive interactions between side chains that minimize the benzene ring twisting along the backbone structure. At the surfactant's critical micelle concentration, the P2 chains wrap around the outer surface of the SDS micelles. This work has implications on the development of new stable poly(p-phenylenevinylene)-based photovoltaic and electroluminescent materials with tunable optical properties.

Interaction between casein and sodium dodecyl sulfate

The interaction of the anionic surfactant sodium dodecyl sulfate (SDS) with 2.0 mg/ml casein was first investigated using isothermal titration calorimetry (ITC), dynamic light scattering (DLS), and fluorescence spectra. ITC results show that individual SDS molecules first bind to casein micelles by the hydrophobic interaction. The micelle-like SDS aggregate is formed on the casein chains when SDS concentration reaches the critical aggregation concentration (c1), which is far below the critical micellar concentration (cmc) of SDS in the absence of casein. With the further increase of SDS concentration to the saturate binding concentration c2, SDS molecules no longer bind to the casein chains, and free SDS micelles coexist with casein micelles bound with SDS aggregates in the system. DLS results show that the addition of SDS leads to an increase in the hydrodynamic radius of casein micelles with bound surfactant at SDS concentration higher than 4 mM, and also an increase in the casein monomer molecule (or submicelles) at SDS concentration higher than 10 mM. Fluorometric results suggest the addition of SDS leads to some changes in the binding process of hydrophobic probes to casein micelles.

Nonlinear Response of a Batch BZ Oscillator to the Addition of the Anionic Surfactant Sodium Dodecyl Sulfate

The response of the Belousov-Zhabotinsy (BZ) system to the addition of increasing amounts of the anionic surfactant sodium dodecyl sulfate (SDS) was monitored at 25.0 degrees C in stirred batch conditions. The presence of SDS in the reaction mixture influences the oscillatory parameters, i.e., induction period and oscillation period, to an extent that depends on the surfactant concentration. The experimental results have shown that the induction period increases slightly on increasing surfactant concentration and, then, a further increase in the [SDS] leads to an enhancement while the oscillation period increases monotonously on increasing SDS concentration. It has been proposed that the response of the oscillatory BZ system to the addition of SDS is due to the peculiar capability of the organized surfactant assemblies to affect the reactivity by selectively sequestering some key reacting species. Indeed, explanations of the experimental results have been given on the basis of the role played by the micellar shape, which in turn dictates the hydrophobic nature. The suggested perturbation effects have been supported by performing viscosity measurements on the aqueous SDS solutions and by the spectrophotometric estimation of the binding constant of the bromine species to the micellar aggregates. This study has indirectly corroborated the existence of two kind of micelles and unambiguously revealed that the bromine species show a different affinity toward the spherical and rod-like micelles.

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.

Analysis of gelatin chain aggregation in dilute aqueous solutions through viscosity data

Viscosity data of gelatin solutions with concentrations between 10 −5 and 10 −3 g/cm 3 are studied in a horizontal capillary viscometer for a wide range of shear rates, covering the dilute and very dilute zones, where either intermolecular aggregation and intramolecular folding are possible, respectively, and the sol–gel transition is not observed. It is found that the dilute solutions behave as Newtonian fluids for the range of shear rates studied. Intrinsic viscosity values revealed that the maturation temperature has a relevant influence on the type of chain aggregations forming thermo-reversible clusters. The use of potassium thiocyanate and urea partially inhibited cluster formations. On the contrary, the aggregation process was not modified with the addition of surfactant sodium dodecylsulphate, indicating that hydrophobic interactions were not the cause of this phenomenon. The evolution of cluster formations in the dilute zone was analyzed through Smoluchowski aggregation theory and the aggregate-size distribution function was evaluated allowing one to conclude that it tends to be Gaussian and high polydisperse as the maturation time increases. Calculations show that disordered aggregates with high amount of occluded solvent are formed at low temperatures, while for higher temperatures, more compact structures are attained. Through the evaluation of the colloidal stability ratio, it is shown that the aggregation process is very slow in the dilute zone with an energetic barrier of around 25 times the Brownian thermal energy, and that the possibility of significant aggregation in the very dilute zone must be excluded.

Interaction of unmodified and hydrophobically modified alginate with sodium dodecyl sulfate in dilute aqueous solution: Calorimetric, rheological, and turbidity studies

Interactions between hydrophobically modified alginate (HM-alginate) and the anionic surfactant sodium dodecyl sulfate (SDS) have been investigated by microcalorimetry, rheology and turbidimetry. Significant polymer–surfactant interactions were observed between HM-alginate and SDS, whereas for mixtures of unmodified alginate and SDS only a weak synergism was detected. The intrinsic viscosity of HM-alginate solutions with added SDS showed a strong upturn at low SDS concentrations, indicating a polyelectrolyte effect. The zero-shear viscosity of the semidilute HM-alginate solution was found to increase at a low level of SDS addition, and then decrease with increasing SDS concentration. The turbidity curves exhibit the same profile as those of the viscosity. The maximum of the turbidity is located at the same SDS concentration as the viscosity maximum for the semidilute solution. This picture is consistent with the conjecture of the formation and breakup of the associations as the SDS concentration increases.