High Sodium Dodecyl Sulfate Concentrations Research Articles

Interactions between Poly(N-vinylformamide) and Sodium Dodecyl Sulfate As Studied by Fluorescence and Two-Dimensional NOE NMR Spectroscopy

The interaction of poly(N-vinylformamide) (PNVF) with anionic surfactant, sodium dodecyl sulfate (SDS), has been studied by pyrene fluorescence and two-dimensional nuclear Overhauser effect spectroscopy (2D NOESY). With use of pyrene as the probe, from low to high concentration of SDS, the pyrene I1/I3 plot exhibits three stages of association of PNVF with SDS. The I1/I3 plot vs [SDS] shows a well-defined plateau (I1/I3 = 1.47) at SDS concentrations ranging between 3 and 10 mM, indicating that in this range of SDS concentrations the sizes of polymer-bound SDS aggregates are approximately identical. The ambiguity in determining the critical aggregation concentration (cac) of SDS from the I1/I3 plot vs [SDS], which resembles the typical profile of surface tension vs surfactant concentration, has been clarified by the 2D NOESY experiment. Also, just beyond the cac ([SDS] = 3 mM), definite proof of formation of the PNVF−SDS complex bound on the polymer chain is provided by the 2D NOESY experiments. On the bas...

Fabrication of Dispersed Permalloy Nanoparticles by Pulsed Laser Ablation in Aqua

ABSTRACTPermalloy (Ni81Fe19) nanoparticles with diameters of hundreds of nanometers have been successfully fabricated by pulsed laser ablation (PLA) in air, distilled water, pure ethanol and sodium dodecyl sulfate (SDS) aqueous solutions. The permalloy nanoparticles made in SDS solutions are typically spherical in shape. Lower laser energy with lower frequency leads to the formation of smaller permalloy nanoparticles. Higher concentration of SDS results in smaller nanoparticles. Lastly, we found some unusual permalloy nanoparticles with interesting morphologies made by PLA in air, distilled water and ethanol.

Adsorption of sodium dodecyl sulfate on the bismuth (1 1 1), (0 0 1) and [formula omitted] planes

Impedance spectroscopy has been employed for a quantitative study of sodium dodecyl sulfate (SDS) adsorption kinetics at the Bi( h k l) electrodes. Analysis of the impedance data demonstrates that the adsorption process of SDS at high negative surface charge density is limited by the rate of the diffusion and heterogeneous adsorption steps (mixed kinetics). At small ac frequency and higher SDS concentrations, two-dimensional association or semimicelle formation of the SDS is possible in the adsorption layer. The double layer and adsorption capacitances and diffusion resistance depend on the electrode potential, adsorbate concentration and Bi( h k l) structure. The thermodynamic adsorption parameters have been calculated using modified Frumkin–Damaskin adsorption theory. The Gibbs adsorption energy, attraction interaction constant, limiting capacitance and limiting adsorption potential shift and Gibbs adsorption depend on the Bi( h k l) structure studied.

Anomalous turbidity, dynamical, and rheological properties in aqueous mixtures of a thermoresponsive PVCL-g-C 11EO 42 copolymer and an anionic surfactant

Thermoresponsive associations in aqueous mixtures of the anionic sodium dodecyl sulfate (SDS) surfactant and copolymers of poly( N-vinylcaprolactam) and ω-methoxy poly(ethylene oxide) undecyl α-methacrylate (PVCL-g-C 11EO 42) have been characterized using turbidimetry, rheology, and dynamic light scattering (DLS). The cloud point (CP) is shifted toward higher temperature as the percentage of surfactant increases in the PVCL-g-C 11EO 42/SDS mixture, and at low copolymer concentration and high level of SDS addition, the system exhibits a strong polyelectrolyte effect. The polymer concentration dependence of CP in the dilute regime can be described by a power law CP (°C) = k × c − ν , where the values of k and ν rise with increasing SDS concentration. For semidilute polymer solutions, an abnormal cloud point minimum is observed at a certain polymer–surfactant composition. In the turbidity-temperature curves, a novel anomaly is detected for semidilute polymer solutions at certain levels of surfactant addition. The shear viscosity always exhibits Newtonian behavior even at high polymer concentrations, suggesting that the polymer chains are unentangled and not forming an interconnected network. For semidilute polymer solutions and moderate levels of surfactant addition, the viscosity results indicate a temperature-induced compression of the polymer–surfactant clusters. At a given temperature, high surfactant concentration leads to an expansion of the complexes. DLS results on PVCL-g-C 11EO 42/SDS mixtures at temperatures approaching the CP show the existence of a bimodal relaxation process with a fast mode associated with the diffusion of individual molecules, or small clusters of molecules, and a slow mode portraying interchain aggregation and the formation of aggregates. At temperatures where the systems approach CP, large interchain aggregates are formed. At high SDS concentrations, a temperature increase gives rise to shrinkage of the polymer–surfactant complexes. At this stage, the solvent power is enhanced and together with the repulsive electrostatic interactions the tendency of the system to evolve further interchain associations is suppressed.

Influence of Ionic Charges on the Bilayers of Lamellar Phases

The influence of ionic charges on the mesophases in the ternary system of C(12-16)E(6) (LA 070), ethylhexylglycerid (EHG), and water was studied. The charge was introduced by adding the ionic surfactant SDS (sodium dodecyl sulfate). The single lamellar phase (5 wt % LA 070 and 240 mM EHG in water) yields a bluish homogeneous solution. With the addition of SDS, the samples become more and more clear. Rheology measurements indicate that increased charge density increases the storage modulus G', and the lamellar phases show typical behavior of a viscoelastic fluid with a yield stress at higher SDS concentration. SAXS measurements show that the interlamellar distance D decreases with SDS concentration. The addition of ionic surfactants suppresses the Helfrich undulations, flattens the bilayers, and decreases interbilayer spacing due to electrostatic repulsions of the ionic surfactant head groups. Furthermore, the L(alpha) phase transforms into vesicle phases as the SDS concentration is increased. Second, it is shown that with added NaCl electrolyte the phase with charged surfactant behaves again in the same way as the initial uncharged system. The addition of salt screens the electrostatic interaction, which leads to a higher flexibility of the bilayers and a decrease of the storage modulus G'. Theoretical calculations show that the shear moduli of the L(alpha) phases are much smaller than the osmotic pressure of the systems. Several models are proposed for the explanation of the shear moduli. The model due to Lekkerkerker for the electric contribution of the bending constant of the bilayer seems to yield good results for the transition to vesicles.

Supramolecular Complex Induced by the Binding of Sodium Dodecyl Sulfate to PAMAM Dendrimers

Isothermal titration calorimetry (ITC) and dynamic light scattering (DLS) were employed to study the spontaneous supramolecular complexation of amine terminated PAMAM dendrimer (G3[EDA] PAMAM-NH2) induced by the binding of an anionic surfactant, sodium dodecyl sulfate (SDS). At pH<or=2, SDS molecules bound to protonated amines on the outer rims of G3[EDA] PAMAM-NH2 driven by electrostatic interaction, which induced the formation of PAMAM/SDS supramolecular complex via hydrophobic association between bound SDS molecules. The complex with radius of approximately 37 nm was observed at SDS concentration as low as 0.02 mM (in 0.2 mM PAMAM). The size of the complex increased progressively with increasing SDS concentration and precipitated when the SDS concentration exceeded 15 mM. At pH of approximately 7.4, the formation of PAMAM/SDS complex was observed at higher SDS concentration (0.1 mM in 0.2 mM PAMAM), and it resolubilized with further increase of SDS concentration to approximately 18 mM due to weaker electrostatic interaction at higher pH. At pH>or=10, the electrostatic binding ceased because the deprotonated PAMAM dendrimer was uncharged, and hence the surfactant-induced supramolecular assembly could not be formed.

Effects of Tx-100-SDS on crystal growth of calcium carbonate in reverse microemulsion solution

Syntheses of CaCO3 crystals in reverse microemulsion solutions containing 1-(1,1,3,3-tetramethylbutyl)-4-hydroxypolyethoxybenzene (Tx-100), sodium dodecyl sulfate (SDS) and their equimolar mixture were carried out at room temperature respectively. The crystal phase of CaCO3 is changed from calcite at low concentrations to vaterite at high concentrations of SDS and Tx-100. From rods at low concentration to olivary spheres at high concentration, SDS can influence the morphology of CaCO3 significantly, while almost no such effect for Tx-100. Hollow spheres, olivary spheres and even two fused olivary spheres of CaCO3 were produced at different concentrations of Tx-100-SDS, and the variation of crystal phase is opposite to that in the presence of SDS or Tx-100 alone. The effects of interaction of SDS with Tx-100 on morphology and crystal phase of CaCO3 were discussed. It was estimated to put forward that the formation of hollow CaCO3 crystals was caused by the collaborating actions of SDS template and TX-100 inhibition.

Aqueous Two-Phase System Formation Kinetics for Elastin-Like Polypeptides of Varying Chain Length

The kinetics of aqueous two-phase system (ATPS) formation for elastin-like polypeptides (ELP) with defined chemical composition and chain length was investigated by dark field microscopy in an on-chip format with a linear temperature gradient. Scattering intensities from peptide solutions in the presence and absence of sodium dodecyl sulfate (SDS) were recorded as a function of temperature and time, simultaneously. It was found that the formation of the ATPS for three ELPs of different molecular weights (36 075, 59 422, and 129 856 Da) in the absence of SDS followed a coalescence mechanism, and the rate constant and activation energy were independent of chain length. With the introduction of SDS into the ELP solutions, the rate constants were attenuated more strongly with increasing chain length. Moreover, the coalescence process in the presence of SDS showed non-Arrhenius kinetics as a function of temperature. For the two shorter ELPs, ATPS formation occurred via coalescence at all SDS concentrations and temperatures investigated. On the other hand, the coalescence process was greatly suppressed for the longest ELP at elevated temperatures and higher SDS concentrations. Under these circumstances, ATPS formation was forced to proceed via a mixed Ostwald ripening and coalescence mechanism.

Keratin–rhamnolipids and keratin–sodium dodecyl sulfate interactions at the air/water interface

Keratin–surfactant interactions at the air/solution interface may be indicative for skin irritation by surfactants. In this study pure keratin was extracted from chicken feathers as described by Schrooyen at al. [1,2] and the adsorption properties of biologically produced rhamnolipids (RL) and sodium dodecyl sulfate (SDS) mixed with keratin molecules were investigated by surface tension measurements. Keratin was added in three specific amounts to RL and SDS aqueous solutions of varying concentrations, respectively, and keratin–RL and keratin–SDS interactions were investigated at pH 6.2 and 5.0. The surface tension measurements showed that surfactant–keratin complexes were formed in the solutions at pH 6.2. At low RL concentrations the added amount of keratin decreased the surface tension as a result of the hydrophobic keratin–RL complexes formed, which have covered the air/solution interface. Beginning from moderate RL concentrations, less surface active keratin–RL complexes were formed due to hydrophilization of the former complexes and they were removed from the interface to the bulk phase as a result of the competitive adsorption mechanism and pure RL molecules covered the interface gradually. At low SDS concentrations surface tension decrease was also observed by the covering of the air/solution interface with keratin–SDS complexes. At moderate SDS concentrations the keratin–SDS complexes exhibited a more surface active feature. Unlike the keratin–RL complexes, they have remained at the interface until the higher SDS concentrations and keratin ratios. However, at the minimum surface tension value of the pure SDS at its CMC value, the surface tension of the keratin–SDS mixture reached the value of pure SDS solution and the air/solution interface has been covered again only with pure SDS monomers. The keratin–surfactant solutions prepared at pH 5 showed lower surface tension values compared to that measured at pH 6.2 and the surface tension behavior of RL and SDS resembled each other. Above a certain surfactant concentration the addition of keratin to surfactant solutions rendered the surface less surface active compared to their pure surfactant solutions at pH 5.0. The consideration of the surface tension behavior of two anionic surfactants has shown that the RL–keratin interactions are milder than SDS–keratin interactions at pH 6.2 and 5.0.

Composition/Structural Evolution and Optical Properties of ZnO/Zn Nanoparticles by Laser Ablation in Liquid Media

We present composition-controlled synthesis of ZnO-Zn composite nanoparticles by laser ablation of a zinc metal target in pure water or in aqueous solution of sodium dodecyl sulfate (SDS). By SDS concentration, composition and size of the nanoparticles can be controlled in a wide range. Relative amounts of the components Zn and ZnO, the particle size, and the microstructure can evolve with SDS concentration in solution. High SDS concentration corresponds to high relative amount of Zn nanoparticles existing as the core in the core/shell nanostructures, whereas low SDS concentration leads to high ZnO amount. This was explained by a dynamic mechanism on the basis of the competition between aqueous oxidation and SDS capping protection. Correspondingly, optical absorption spectra evolve from the excitonic peak of ZnO (about 350 nm) to the Zn surface plasmon resonance (about 242 nm) with rise of SDS concentration. A blue (about 450 nm) photoluminescence was observed in the obtained ZnO nanoparticles, which was attributed to existence of interstitial zinc in ZnO lattices. This study has revealed that laser ablation of active metal in liquid media is an appropriate method to synthesize a series of metal oxide semiconductor-metal composite nanoparticles with controlled composition and size.

On-Probe Sample Preparation without Washes for Matrix-Assisted Laser Desorption/Ionization Mass Spectrometry Using an Anion Exchange Medium

When the mass spectra of biological samples (proteins, peptides, and so on) are obtained routinely by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), a serious problem is the reduction of the ionization efficiency by impurities, such as buffer salts and detergents. We focused our attention on devising a method to maintain the ionization efficiency of protein samples, even in the presence of sodium dodecyl sulfate (SDS), without any extra purification step. Although no protein ion peaks are observed in the presence of 2.5% SDS with the usual methods, the addition of a granular anion exchange silica gel to the matrix solution allowed the protein ion peaks to be obtained with an excellent signal-to-noise ratio. Together with other supporting experiments, we suggest that the positively charged surface (the basic environment derived from the anion exchange groups) and the roughness of the particles were important for good ionization in the presence of a high SDS concentration. For a very uneven surface, the SDS might be absorbed into the particle interiors during the process of cocrystallization with the matrix and analytes, which is known as the molecular sieve effect, and the SDS concentration in the surface crystalline film might be reduced. As a result, we developed an on-probe sample preparation method without washes for MALDI, using a strong anion exchange silica gel. This method is applicable even in the presence of 2.5% SDS, and is not only very simple but also inexpensive, because it can be used with the standard MALDI target plates.

Phase separation and structural properties of semidilute aqueous mixtures of ethyl(hydroxyethyl)cellulose and an ionic surfactant

Turbidity and small-angle neutron scattering (SANS) measurements have been carried out over an extended temperature range (10–60 °C) on thermoreversible gelling and non-gelling semidilute aqueous systems of ethyl(hydroxyethyl)cellulose (EHEC) in the presence of various amounts of sodium dodecyl sulfate (SDS). EHEC dissolved in D 2O exhibits a lower consolute solution temperature with an abrupt change of the turbidity upon heating the sample. The turbidity transformation is shifted toward higher temperatures (the cloud point temperature rises) and it becomes gradually gentler as the level of surfactant addition increases. Precision turbidity measurements demonstrate the existence of hysteresis effects when heating and cooling scans are conducted. This effect is reduced with SDS addition and disappears at a sufficiently high SDS concentration where most aggregates are disrupted. It is shown from temperature quench turbidity experiments that it takes a very long time for the temperature-induced complexes to disintegrate. The scattered intensity results from SANS at low values of the scattering vector ( q) disclose that elevated temperature and low SDS concentration promote the formation of large-scale associations, and at higher levels of surfactant addition the tendency to form aggregates is suppressed. At high surfactant concentrations (8 and 16 m m), an interaction peak appears in the spectrum at intermediate values of q. For the EHEC sample with 8 m m SDS, the peak disappears at higher temperatures because of enhanced hydrophobicity of the polymer. The analysis of the SANS data for the gelling sample (EHEC with 4 m m SDS) reveals that the inhomogeneity of the gel becomes more pronounced in the post-gel region.

Cationic Amphiphilic Polyelectrolytes and Oppositely Charged Surfactants at the Silica−Aqueous Interface

The influence of sodium dodecyl sulfate (SDS) on the interfacial behavior of two amphiphilic polyelectrolytes, which are copolymers of the cationic monomers triethyl(vinylbenzyl)ammonium chloride and dimethyldodecyl(vinylbenzyl)ammonium chloride, at the silica-aqueous interface was studied. The fraction of amphiphilic monomers was varied, where 0DT, 40DT, and 80DT contained 0, 40, and 80 mol % monomers with dodecyl side chains, respectively. We used in situ ellipsometry to follow the kinetics of adsorption, in terms of adsorbed amount and adsorbed layer thickness, as well as the response of the adsorbed layers to changes in ionic strength and surfactant concentration. Different results were obtained when surfactant was added to the preadsorbed layers compared to the cases when complexes were preformed in the solution prior to the adsorption. In the whole range of concentrations studied, SDS interacts with 40DT and 80DT noncooperatively, whereas for 0DT cooperativity of binding is observed. The amount adsorbed increased significantly as the SDS concentration was close to the cmc. At high SDS concentrations, a lowering of the layer density was observed. For the amphiphilic polyelectrolytes, 40 DT and 80DT, no desorption from the interface was detected for the range of SDS concentrations studied, while 0DT features a maximum in adsorbed amount at concentrations close to the cmc of SDS. Adsorption of 40DT and 80DT from their mixtures with SDS is found to be path dependent with respect to the variation in SDS concentration, where the reversibility decreases with increasing SDS concentration above the expected charge neutralization point. The coadsorption of 80DT and SDS is highly irreversible with respect to changes in the ionic strength within the time scale of the experiment. In this study, we attempt to illustrate both general mechanisms and specific effects. With regard to the general behavior, it is important to note the charge regulation of both the silica surfaces and the polyion/surfactant complexes; an interplay between the two charge-regulating effects is the key to understanding our observations.

The Synthesis of Hydrophobically Modified Water‐Soluble Polyzwitterionic Copolymers and Responsiveness to Surfactants in Aqueous Solution#

A novel zwitterionic surfactant monomer containing a carboxybetaine moiety and a 10 carbon aliphatic tail was synthesized and copolymerized with acrylamide to yield a water‐soluble, hydrophobically modified zwitterionic polymer [Poly(acrylamide‐co‐(3‐(N,N‐dimethyl‐N‐3′‐(N′‐acryloyl)aza‐tridecyl) ammonio butanoate))]. The response of aqueous polymer solutions to the addition of various classes of surfactant was investigated and compared to that of an analogous novel polymer containing the sulfobetaine zwitterion [Poly(acrylamide‐co‐(N,N‐dimethyl‐N‐3′‐(N′‐acryloyl) aza‐tridecyl) ammonio propane sulfonate))]. It was found that the addition of sodium dodecyl sulfate (SDS) produced a pronounced maximum in viscosity, while dodecyltrimethylammoniumbromide (DTAB), N‐dodecyl‐N,N‐dimethylammonio‐1‐propanesulfonate (SB3‐12), and Triton X‐100 either had no effect, or produced a decrease in viscosity. The effect of pH on polymer–SDS interaction was also studied. Lowering pH increased the SDS–polymer interaction and significantly shifted viscosity enhancement to a higher SDS concentration. #Paper Number 108 in a series entitled Water Soluble Polymers.

Mechanisms of Solubilization of Mixed Liposomes: Preferential Dissolution of Liposome Components

The mechanism of vesicle-to-micelle transformation due to the interactions with sodium dodecylsulfate (SDS) has been studied by monitoring changes in the optical density, surface tension, SDS monomer concentrations, pyrene fluorescence, and mass spectrometry. Two inflection points appeared on the optical density as well as effective hydrodynamic diameter curves. Based on the results of the surface tension and SDS monomer measurements, the first inflection point is attributed to the saturation of bilayers by SDS monomers and the onset of liposome solubilization processes. The second inflection point corresponds to the onset of complete disruption of bilayers and the critical micelle concentration of the mixed systems. The fluorescence results show the core of the mixed micelles to be more hydrophobic than that of the SDS micelles, suggesting that liposome solubilization is a micellization process. From the individual phospholipid liposome solubilization studies, it was found that phosphatidic acid (PA) molecules are more susceptible toward SDS. Interestingly, it has been detected from the mass spectra that the disruption of liposome bilayers is a preferential dissolution process. It is proposed that, at low SDS concentration, PA molecules preferentially exit first from the mixed liposome bilayers (1:1 PA/phosphatidylcholine), causing liposome solubilization. In contrast, at high SDS concentrations, the breakdown of liposome takes place instantaneously.

In Situ Mechanistic Study of SDS Adsorption on Hematite for Optimized Froth Flotation

An in situ attenuated total reflectance Fourier transform infrared (ATR-FTIR) technique has been developed to study the adsorption of sodium dodecyl sulfate (SDS) onto pure, colloidal hematite as a function of both concentration and pH. The absorption bands of methyl and methylene groups are most reliable for quantifying adsorption unambiguously. The infrared spectral results have been correlated with ζ-potential studies to establish an absence of adsorption above the iso-electric point of 7.3, and to indicate that the mechanism of adsorption is physical, involving reversible electrostatic and hydrophobic forces. In the same way, there is no evidence for the existence of chemisorption. This is supported in the spectral results by the absence of shifts in relative band intensities and the absence of new adsorption bands. At low pH and high SDS concentrations, the adsorption is sufficient to cause a reversal in sign of the ζ-potential. Spectral absorption measurements should be made under in situ conditions to obtain unambiguous results. Studies of adsorption on natural hematite indicate a high depletion of SDS from solution at low pH; the measurements are consistent with precipitation losses due to the presence of calcium and ferric ions. This precipitation leads to a drop in flotation recovery. At high pH, adsorption occurs onto mineral particles which have become coated with carbonate mineral, leading to a flat variation of recovery with pH. The results have enabled optimum flotation conditions to be defined. Recovery can be directly related to adsorption density at moderate pH below the iso-electric point. The optimum pH for flotation is 5; extremes of pH are detrimental to flotation recovery of pure mineral and should be avoided. Low pH causes surfactant precipitation, while high pH will lead to surface transformation of the mineral. A collector concentration of 0.05 times the critical micelle concentration, corresponding to partial monolayer coverage on the hematite surface, is sufficient to ensure good recovery.

Adsorption of cationic cellulose derivative/anionic surfactant complexes onto solid surfaces. II. Hydrophobized silica surfaces.

The effect of the anionic surfactant SDS (sodium dodecyl sulfate) on the adsorption behavior of cationic hydroxyethyl cellulose (Polymer JR-400) and hydrophobically modified cationic cellulose (Quatrisoft LM-200) at hydrophobized silica has been investigated by null ellipsometry and compared with the previous data for adsorption onto hydrophilic silica surfaces. The adsorbed amount of LM-200 is found to be considerably larger than the adsorbed amount of JR-400 at both surfaces. Both polymers had higher affinity toward hydrophobized silica than to silica. The effect of SDS on polymer adsorption was studied under two different conditions: adsorption of polymer/SDS complexes from premixed solutions and addition of SDS to preadsorbed polymer layers. Association of the surfactant to the polymer seems to control the interfacial behavior, which depends on the surfactant concentration. For the JR-400/SDS complex, the adsorbed amount on hydrophobized silica started to increase progressively from much lower SDS concentrations, while the adsorbed amount on silica increased sharply only slightly below the phase separation region. For the LM-200/SDS complex, the adsorbed amounts increased progressively from very low SDS concentrations at both surfaces, and no large difference in the adsorption behavior was observed between two surfaces below the phase separation region. The complex desorbed from the surface at high SDS concentrations above the critical micelle concentration. The reversibility of the adsorption of polymer/SDS complexes upon rinsing was also investigated. When the premixed polymer/SDS solutions at high SDS concentrations (>5 mM) were diluted by adding water, the adsorbed amount increased due to the precipitation of the complex. The effect of the rinsing process on the adsorbed layer was determined by the hydrophobicity of the polymer and the surface.

Investigation of the Interaction between Sodium Dodecyl Sulfate and Cationic Polymers

Aggregation properties of sodium dodecyl sulfate (SDS) on a cationic hydroxyethyl cellulose, Polyquaternium-10 (PQ-10), of low charge density were studied by potentiometric and pyrene fluorescence methods and compared with those of poly(diallyldimethylammomium chloride) (PDADMAC) of high charge density. The critical aggregation concentration (cac) was measured with the potentiometric method and further confirmed with the fluorescence method. The former was found to be more accurate. The value of the cac for the SDS/PQ-10 system was measured at 100, 200, and 400 ppm polymer and at 288.2,298.2, and 308.2 K. They showed almost the same cac value, 0.04 mmol dm-3. The I1/I3 value of the pyrene fluorescence spectrum in the SDS/PQ-10 system at higher SDS concentration was smaller than that in SDS/PDADMAC solution and much larger than that of water. From the binding isotherm by the potentiometric method, the free DS- concentration (Cf) and the bound DS- concentration (Cb) could be evaluated with ease over the SDS concentration range above the cac. The aggregation number of DS- aggregates for both the above polymers was evaluated from the fluorescence quenching method using the values of Cf and Cb from the potentiometric method. Because Cf in the SDS/PQ-10 system above the cac did not maintain a constant value contrary to that in the SDS/PDADMAC system but increased quite a lot, Cb should not be regarded as [SDS] - cac above the cac. The aggregation number in the SDS/PQ-10 system increased almost linearly with increasing total concentration of SDS, while that in the SDS/PDADMAC system reached a plateau. With increasing temperature, the aggregation number of the SDS/PDADMAC system decreased more rapidly than that of the SDS/PQ-10 system.

Isothermal Titration Calorimetric Studies on the Temperature Dependence of Binding Interactions between Poly(propylene glycol)s and Sodium Dodecyl Sulfate

Isothermal titration calorimetry (ITC) is a sensitive research tool for examining the binding interactions between surfactant and polymer where the differential enthalpy during the binding process is monitored. In addition to the critical micelle concentration (cmc) and the micellization enthalpy (deltaHm), the effective micellar charge fraction (beta) of the ionic surfactant micellization process can also be determined from ITC thermograms. Poly(propylene glycol) (PPG) exhibits a lower critical solution temperature (LCST) ranging from 15 to 42 degrees C, depending on the molecular weights. We report, for the first time, the binding interactions between sodium dodecyl sulfate (SDS) and 1,000, 2,000 and 3,000 Da PPGs, where different binding mechanisms are in operation, depending on the temperature. At temperatures lower than the LCST, the binding interactions are similar to those of SDS and low molecular weight poly(ethylene glycol)s (MW < 3500 Da). At temperatures greater than the LCST, the binding interactions are dominated by direct solubilization of PPG chains into mixed micellar cores. At temperatures near the LCST, the binding interactions are controlled by the balance ofthe PPG solubilization at low SDS concentrations and polymer-induced micellization at high SDS concentrations.

Adsorption of Cationic Cellulose Derivatives/Anionic Surfactant Complexes onto Solid Surfaces. I. Silica Surfaces

The effect of the anionic surfactant SDS (sodium dodecyl sulfate) on the adsorption behaviors of cationic hydroxyethyl celluloses (Polymer JR-125, JR-400, and JR-30M) and hydrophobically modified cationic cellulose (Quatrisoft LM-200) at silica surfaces in the presence of a 10 mM NaCl solution has been investigated by null ellipsometry. The adsorbed amount of LM-200 is found to be considerably larger than adsorbed amounts of other polymers. The rate of adsorption for the LM-200 is also lower than that for the Polymer JR series under comparable conditions. Electrostatic interaction is found to be the major driving force for the adsorption. The effect of SDS on adsorption was studied under two different conditions: adsorption of polymer/SDS complexes from premixed solutions and additions of SDS to the preadsorbed polymer layers. In all cases, associative binding of the surfactant to the polymer seems to control interfacial behavior, which depends on the surfactant concentration. Maximum adsorption was obtained at the surfactant concentration below the phase separation region, and the complex desorbed from the surface at a high SDS concentration above the critical micelle concentration. The reversibility of the polymer/SDS complexes adsorption upon rinsing with NaCl solutions was also investigated. When the premixed polymer/SDS solutions at high SDS concentrations (>5 mM) were diluted by salt solutions, the adsorbed amount increased sharply with precipitation of the complex. A larger amount of the JR-400/SDS complex precipitated during the rinsing process seemed to adsorb to a larger extent to silica than the corresponding LM-200/SDS complex.