Complexation of hydrophobically modified polyelectrolytes with surfactants: anionic poly(maleic acid/octyl vinyl ether)/anionic sodium dodecyl sulfate

Interactions of surfactants with hydrophobically modified polyelectrolytes in aqueous solutions are important in several applications such as detergents, cosmetics, foods, and paints. Fundamental questions arise on the mechanisms of complexation of the polyelectrolyte and surfactant that control their behavior. In this work, the complexation was studied by examining interactions in aqueous solutions of a hydrophobically modified polymer, poly(maleic acid/octyl vinyl ether) (PMAOVE), with sodium dodecyl sulfate (SDS) by monitoring viscosity, pyrene solubility, light scattering, and analytical ultracentrifugation. When the anionic surfactant SDS was added to aqueous solutions of the similarly charged polymer PMAOVE, the surfactant was incorporated into the hydrophobic nanodomains of PMAOVE even far below the cmc of the surfactant. On the basis of viscosity, pyrene solubility, and analytical ultracentrifugation data, it is proposed that PMAOVE undergoes structural unfolding and at higher SDS concentrations mixed micelles are formed.     

Electrochemical determination of tyrosine in the presence of uric acid at a carbon paste electrode modified with multi-walled carbon nanotubes enhanced by sodium dodecyl sulfate

Tyrosine (Tyr) was quantitated with high sensitivity and selectivity in the presence of uric acid (UA) using a carbon paste electrode modified with multi-walled carbon nanotubes. Tyr and UA were catalytically oxidized with diffusion-controlled characteristics. They were determined simultaneously by differential pulse voltammetry with a potential difference of 350 mV. The electrocatalytic currents increase linearly with Tyr and UA concentrations 4×10^?7?1×10^?4 M and 3×10^?7?2×10^?4 M. Their detection limits were 1×10^?7 and 5.1×10^?8 M respectively. In the presence of sodium dodecyl sulfate the Tyr detection limit improved from 1×10^?7 to 6.9×10^?8 M. The electrode was successfully used to quantitate Tyr and UA in serum.      

Preconcentration and voltammetric determination of palladium (II) at sodium humate modified carbon paste electrodes

A chemically modified carbon paste electrode was prepared by incorporating appropriate amounts of sodium humate(NaA). Palladium(II) was selectively accumulated in a solution of Britton-Robinson(B-R) buffer (pH 2.8) onto the electrode surface in open circuit mode. The subsequent electrochemical measurement was carried out by cyclic voltammetry (CV) and linear sweep anodic stripping voltammetry (LSASV) in a supporting electrolyte of 1.0 M HCl. The obtained oxidation currents (I_pa1 and L_pa2) were proportional to the Pd(II) concentration in the range of 4.7 × 10^–6 - 9.4 × 10^–8 M. The developed method was applied to the quantitative determination of palladium in real samples.     

Preconcentration and voltammetric determination of palladium (II) at sodium humate modified carbon paste electrodes

A chemically modified carbon paste electrode was prepared by incorporating appropriate amounts of sodium humate(NaA). Palladium(II) was selectively accumulated in a solution of Britton-Robinson(B-R) buffer (pH 2.8) onto the electrode surface in open circuit mode. The subsequent electrochemical measurement was carried out by cyclic voltammetry (CV) and linear sweep anodic stripping voltammetry (LSASV) in a supporting electrolyte of 1.0 M HCl. The obtained oxidation currents (I_pa1 and L_pa2) were proportional to the Pd(II) concentration in the range of 4.7 × 10^–6 - 9.4 × 10^–8 M. The developed method was applied to the quantitative determination of palladium in real samples. Received: 6 March 1998 / Revised: 3 June 1998 / Accepted: 3 July 1998     

Self-assembly of poly(allylamine hydrochloride) through electrostatic interaction with sodium dodecyl sulfate

The self-assembly of poly(allylamine hydrochloride) (PAH) through an electrostatic interaction with sodium dodecyl sulfate (SDS) was explored. PAH itself showed no self-assembly in water. A light scattering study demonstrated that PAH formed monodispersed spherical aggregates in water in the presence of SDS. The hydrodynamic diameter of the aggregates was estimated to be ca. 170 nm based on the cumulant analysis. The scattering intensity and UV absorbance at 258 nm based on the aggregation increased with an increase in the molar ratio of SDS to the allylamine hydrochloride unit (SDS/AH), indicating an increase in the number of aggregates. On the other hand, the hydrodynamic diameter of aggregates was constant, i.e., independent of the SDS/AH ratio. The constant size of the aggregates in spite of the increase in the number of aggregates suggests the formation of the micellar aggregates by the intramolecular association through an electrostatic interaction.     

抗坏血酸在聚阿魏酸修饰玻碳电极上的电化学行为研究

研究了抗坏血酸(AA)在聚阿魏酸修饰电极上的电化学性质。在AA存在的条件下,电极过程由扩散控制,测得扩散系数为8.18×10-8cm2/s。AA浓度在0.01~5.0 mmol/L范围内与峰电流呈现良好的线性关系。通过计时安培法测得催化速率常数为8.6×103mol-1.L.s-1。     

Electrochemical sensor for amoxicillin using Cu/poly (<Emphasis Type="Italic">o</Emphasis>-toluidine) (sodium dodecyl sulfate) modified carbon paste electrode

Poly(o-toluidine) (sodium dodecyl sulfate) (POT(SDS)) film was electrosynthesized on carbon paste electrode (CPE) by using the cyclic voltammetry technique in aqueous solution containing o-toluidine (OT), sulfuric acid and SDS. Then, copper oxide was incorporated by immersion of POT(SDS)/CPE in a solution of copper sulfate and using constant potential method. Then, the electrochemical characterization of the modified electrode is presented in alkaline solution. For the first time, electrochemical behaviour of amoxicillin (AMX) at the Cu/POT(SDS)/CPE has been investigated using cyclic voltammetry (CV) and chronoamperometric method. The experimental results suggest that the modified electrode exhibits electrocatalytic effect on the oxidation of AMX resulting in a marked enhancement of the anodic peak current response. Under the selected conditions, the anodic peak current was linearly dependent on the concentration of AMX in the range 80–200 and 5–150 μM with CV and amperometric method, respectively. The detection limits (2δ) were also estimated to be 60 and 3 μM. Some kinetic parameters such as the transfer second-order rate constant (k = 4.9 × 10⁶ cm³ mol^–1 s^–1) of AMX was calculated. Therefore, this modified electrode was a simple, rapid and new electrode to determine AMX in pharmaceutical preparations.     

Sodium dodecyl sulfate modified carbon nanotubes paste electrode as a novel sensor for the simultaneous determination of dopamine,ascorbic acid,and uric acid

A novel modified multiwall carbon nanotubes paste electrode with sodium dodecyl sulfate as a surfactant (SDS) has been fabricated through an electrochemical oxidation procedure and was used to electrochemically detect dopamine (DA), ascorbic acid (AA), uric acid (UA), and their mixture by cyclic voltammetry (CV) and differential voltammetry (DPV) methods. Several factors affecting the electrocatalytic activity of the hybrid material, such as the effect of pH, of the scan rate and of the concentration were studied. The bare carbon nanotubes paste electrode (BCNTPE) and SDS-modified carbon nanotubes paste electrode (SDSMCNTPE) were characterized using Field Emission Scanning Electron Microscopy (FESEM) and Energy-Dispersive X-ray spectroscopy (EDX). Using the CV procedure, a linear analytical curve was observed in the 1 × 10⁻⁶–2.8 × 10⁻⁵ M range with a detection limit at 3.3 × 10⁻⁷ M in pH 6.5, 0.2 M phosphate buffer solutions (PBS).     

Copper(II) modified carbon paste electrodes based on self-assembled mercapto compounds-gold-nanoparticle

Three mercapto compounds [2-mercapto-5-(1-methyl-5-nitroimidazole-2-yl)-1,3,4-thiadiazole] (MMNIT), [2-mercapto-5-(5-nitrofuran-2-yl)-1,3,4-thiadiazole] (MNFT) and [2-mercapto-5-(5-nitrothiophen-2-yl)-1,3,4-thidiazole] (MNTT) were used for self-assembled-gold nanoparticle (SAGNP) modified carbon paste electrodes. The electrodes were applied as indicator electrodes for potentiometric determination of Cu(II) ion. The prepared electrodes exhibit a Nernstian slope of 31.0+/-0.5 mV per decade for Cu(II) ion over a wide concentration range of 7.9x10(-9)-3.2x10(-2), 7.9x10(-9)-7.9x10(-4), and 2.8x10(-8)-7.9x10(-3) mol L(-1) for MMNIT, MNFT and, MNTT, respectively. The detection limits of electrodes were 3.5 (+/-0.2)x10(-9), 4.1x10(-9), and 4.1x10(-8) mol L(-1) of copper ion, respectively. The potentiometric responses of electrodes based on MMNIT, MNFT, and MNTT are independent of the pH of test solution in the pH range 2.0-5.5, 2.5-7.0, and 2.0-6.5, respectively. They have quick response with response time of about 5 s. The proposed electrodes show fairly good selectivity over some alkali, alkaline earth, transition and heavy metal ions. Finally, the proposed electrodes were successfully employed to detect Cu(II) ion in hair and water samples.     

Effect of ethanol on the interaction between poly(vinylpyrrolidone) and sodium dodecyl sulfate

The effect of ethanol on the interaction between the anionic surfactant sodium dodecyl sulfate (SDS) and the nonionic polymer poly(vinylpyrrolidone) (PVP) has been investigated using a range of techniques including surface tension, fluorescence, electron paramagnetic resonance (EPR), small-angle neutron scattering (SANS), and viscosity. Surface tension and fluorescence studies show that the critical micelle concentration (cmc) of the surfactant decreases to a minimum value around 15 wt % ethanol; that is, it follows the cosurfactant effect. However, in the presence of PVP, the onset of the interaction, denoted cmc(1), between the surfactant and the polymer is considerably less dependent on ethanol concentration. The saturation point, cmc(2), however, reflects the behavior of the cmc in that it decreases upon addition of ethanol. This results in a decrease in the amount of surfactant bound to the polymer [C(bound) = cmc(2) - cmc] at saturation. The viscosity of simple PVP solutions depends on ethanol concentration, but since SANS studies show that ethanol has no effect on the polymer conformation, the changes observed in the viscosity reflect the viscosity of the background solvent. There are significant increases in bulk viscosity when the surfactant is added, and these have been correlated with the polymer conformation extracted from an analysis of the SANS data and with the amount of polymer adsorbed at the micelle surface. Competition between ethanol and PVP to occupy the surfactant headgroup region exists; at low ethanol concentration, the PVP displaces the ethanol and the PVP/SDS complex resembles that formed in the absence of the ethanol. At higher ethanol contents, the polymer does not bind to the ethanol-rich micelle surface.     

Adsorption of polyelectrolyte/surfactant mixtures at the air-solution interface: poly(ethyleneimine)/sodium dodecyl sulfate

Neutron reflectivity and surface tension have been used to characterize the adsorption of the polyelectrolyte/ionic surfactant mixture of poly(ethyleneimine) (PEI) and sodium dodecyl sulfate (SDS) at the air-water interface. The surface tension behavior and adsorption patterns show a strong dependence upon the solution pH. However, the SDS adsorption at the interface is unexpectedly most pronounced when the pH is high (when the polymer is essentially a neutral polymer) and when the polymer architecture is branched rather than linear. For both the branched and the linear PEI polymer/surfactant complex formation results in a significant enhancement of the amount of SDS at the interface, down to surfactant concentrations approximately 10(-6) M. For the branched PEI a transition from a monolayer to a multilayer adsorption is observed, which depends on surfactant concentration and pH. In contrast, for the linear polymer, only monolayer adsorption is observed. This substantial increase in the surface activity of SDS by complexation with PEI results in spontaneous emulsification of hexadecane in water and the efficient wetting of hydrophobic substrates such as Teflon. In regions close to charge neutralization the multilayer adsorption is accentuated, and more extensively ordered structures, giving rise to Bragg peaks in the reflectivity data, are evident.     

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     

Microemulsion photopolymerization of methacrylates stabilized with sodium dodecyl sulfate and poly(N-acetylethylenimine) macromonomers

Methyl methacrylate and butyl methacrylate were polymerized in oil-in-water microemulsions that were stabilized by sodium dodecyl sulphate (SDS). A poly(N-acetylethylenimine) (PNAEI) macromer was also included in the recipe, as a cosurfactant and a comonomer. Polymerizations were initiated by UV-irradiation. The average diameters of latex particles, obtained by STM, were in the range of 17-200 nm. The experimental data evidenced that the particle size was mainly dependent on the SDS/PNAEI ratio. Polymerization yields were around 75-85%. The synthesized copolymers have viscosity average molecular weights in the range of 2.1-2.4×10⁶ and glass transition temperatures of 38.0-43.5°C, lower than those obtained without using PNAEI. The investigation by means of FTIR and 1H-NMR techniques revealed that PNAEI was incorporated into the nanoparticles.     

Polymer-surfactant interactions: binding mechanism of sodium dodecyl sulfate to poly(diallyldimethylammonium chloride)

The binding mechanism of poly(diallyldimethylammonium chloride), PDAC, and sodium dodecyl sulfate, SDS, has been comprehensively studied by combining binding isotherms data with microcalorimetry, zeta potential, and conductivity measurements, as well as ab initio quantum mechanical calculations. The obtained results demonstrate that surfactant-polymer interaction is governed by both electrostatic and hydrophobic interactions, and is cooperative in the presence of salt. This binding results in the formation of nanoparticles, which are positively or negatively charged depending on the molar ratio of surfactant to PDAC monomeric units. From microcalorimetry data it was concluded that the exothermic character of the interaction diminishes with the increase in the surfactant/polymer ratio as well as with an increase in electrolyte concentration.     

Association of quaternized poly(4-vinylpyridine) and sodium dodecyl sulfate in water-alcohol solvents

Complexation of a cationic polyelectrolyte (partially quaternized poly(4-vinylpyridine)) and the anionic surfactant sodium dodecyl sulfate in aqueous-organic solutions with different ratios of the components is studied by ion-selective potentiometry, viscometry, spectrophotometry, and microelectrophoresis. Effects of the nature and composition of water-alcohol (methanol, ethanol, and isopropanol) mixtures on the parameters of binding of surfactant ions by polyelectrolytes, the hydrodynamic properties of complexes, and the phase state of the system are examined. The addition of small amounts of ethanol and isopropanol to water (20 vol % ethanol and 10 vol % isopropanol) leads to an increase in the intensity of sodium dodecyl sulfate binding by the polyelectrolyte. The addition of up to 30 vol % methanol is not accompanied by a change in the character of surfactant binding relative to that of the aqueous solution. The relationship between the complexing behavior of the polyelectrolyte and the structural features of mixed solvents is discussed.     

Electroanalysis and simultaneous determination of dopamine and epinephrine at poly(isonicotinic acid)-modified carbon paste electrode in the presence of ascorbic acid

A carbon paste electrode modified with electropolymerized fills of isonicotinic acid was developed.The modified electrode shows excellent electrocatalytic activity toward the oxidation of both dopamine(DA)and epinephrine(EP).Separation of the reduction peak potentials for dopamine and epinephrine was about 357 mV in pH 5.3 phosphate buffer solution(PBS)and the character was used for the detection DA and EP simultaneously.The peak currents increase linearly with DA and EP concentration over the range of 8.0×10-5 to 7.0×10-4 mol/L and 5.0×10-6 to 1.0×10-4 mol/L with detection limits of 2 × 10-5 and 1×10-6 mol/L,respectively.The interference studies showed that the modified electrode exhibits excellent selectivity in the presence of large excess of ascorbic acid(AA).     

Interactions between poly(acrylic acid) and sodium dodecyl sulfate: isothermal titration calorimetric and surfactant ion-selective electrode studies

Interaction between a monodispersed poly(acrylic acid) (PAA) (M(W) = 5670 g/mol, M(w)/M(n) = 1.02) with sodium dodecyl sulfate (SDS) was investigated using isothermal titration calorimetry (ITC), ion-selective electrode (ISE), and dynamic light scattering measurements. Contrary to previous studies, we report for the first time evidence of interaction between SDS and PAA when the degree of neutralization (alpha) of PAA is lower than 0.2. Hydrocarbon chains of SDS cooperatively bind to apolar segments of PAA driven by hydrophobic interaction. The interaction is both enthalpy and entropy favored (deltaH is negative but deltaS is positive). In 0.05 wt % PAA solution, the SDS concentration corresponding to the onset of binding (i.e., CAC) is approximately 2.4 mM and the saturation concentration (i.e., C(S)) is approximately 13.3 mM when alpha = 0. When PAA was neutralized and ionized, the binding was hindered by the enhanced electrostatic repulsion between negatively charged SDS and PAA chains and improved solubility of the polymer. With increasing alpha to 0.2, CAC increases to approximately 6.2 mM, C(S) drops to 8.6 mM, and the interaction is significantly weakened where the amount of bound SDS on PAA is reduced considerably. The values of CAC and C(S) derived from different techniques are in good agreement. The binding results in the formation of mixed micelles on apolar PAA coils, which then expands and dissociates into single PAA chains. The majority of unneutralized PAA molecules exist as single polymer chains stabilized by bound SDS micelles in solution after the saturation concentration.     

Mediated amperometric biosensors for lactic acid based on carbon paste electrodes modified with baker's yeast Saccharomyces cerevisiae

Carbon paste electrodes modified with baker's yeast Saccharomyces cerevisiae (a source of flavocytochrome b(2)) were investigated as amperometric biosensors for lactic acid. Phenazine methosulphate was used as a mediator. The optimal operational conditions of the electrodes were: an operating potential 0.0 V, solution pH 7.2, concentration of phenazine methosulphate in solution 0.2 mM. A linear range in the dependence of the current responses on the concentration of lactic acid was up to 1 mM. The suitability of the electrodes for determination of lactic acid in milk and dairy products such as kefir and yoghurt was tested. The yeast cells in the paste remained viable at least for 1 month.     

Effect of cosolvents on the binding interaction between poly(ethylene oxide) and sodium dodecyl sulfate

The micellization of sodium dodecyl sulfate (SDS) in different glycol-water solvent mixtures was studied using the isothermal titration calorimetric (ITC) technique. At the same time, microcalorimetric titrations were also carried out to monitor the binding interaction of SDS and poly(ethylene oxide) (PEO) in the presence of different cosolvents. The demicellization of SDS in mixtures of water and cosolvents is different from that in water due to the reduction in solvent polarity and charge interaction of surfactants. The critical micelle concentration (cmc) first decreases with the addition of a small amount of cosolvents and then increases at higher cosolvent concentrations. The thermodynamics of surfactant micellization can be analyzed using the solubility parameters of solvent mixtures. For the binding interaction between SDS and PEO in different solvent mixtures, the dehydration process at low SDS concentrations is replaced by the chain solubilization process with decreasing solvent polarity. With further reduction in the solvent polarity, the binding interaction between SDS and PEO becomes weak and no aggregates can be formed beyond a certain glycol concentration. The binding interaction between SDS and PEO in different solvent mixtures was analyzed and ascribed to the effects of PEO solubility and hydrophobicity of SDS.