SDS Systems Research Articles

Assessing nanoparticle-surfactant-salt synergistic effects on droplet–droplet electrocoalescence by molecular dynamics simulations

Electrocoalescence is an energy-efficient and environmentally friendly process for separating water-in-oil emulsions. In this paper, the coalescence behaviors of nanoparticle/surfactant/salt-laden water droplet pairs under direct current (DC) electric fields were investigated by molecular dynamics (MD) simulations. Good qualitative agreements of the present simulations and literature results were obtained. The effects of electric field strengths, surfactant concentrations, and surfactant types on the nanoparticle/surfactant/salt-laden water droplet pair electrocoalescence process were systematically examined, analyzed, and discussed. The results show that the nanoparticle-surfactant-salt synergistic effects mainly include two mechanisms, i.e., the electrostatic interactions of salt ions and surfactant head groups, and the hydrogen bonds of the heteroatoms and water molecules. In addition, strong electric fields lead to high electrocoalescence speed, while weak electric fields result in high electrocoalescence efficiency. At high surfactant concentrations, viscoelastic rigidity of the interface can suppress coalescence, and the aggregations accumulated on the interface result in a significant steric hindrance effect, accounting for the shortest approaching and coalescing time at surfactant number around one single droplet SN = 30 in SDS systems. Regarding the influence of surfactant types, the coalescence efficiencies of the investigated surfactant systems ranked as SDS > Span-80 > Triton X-100 > CTAB. Regarding the nanoparticle-surfactant-salt synergistic effects, in ionic surfactant (CTAB and SDS) systems, the sum of SiO2-Surfactant and Surfactant-NaCl synergistic effects generally dominated the electrocoalescence process; in nonionic surfactant (Span-80 and Triton X-100) systems, the synergistic effects can be generally ranked as SiO2-Surfactant > SiO2-NaCl > Surfactant-NaCl. The results of this work will be potentially valuable for optimizing the design of compact and efficient oil–water separators.

Carbon-Silica Composite as Adsorbent for Removal of Hazardous C.I. Basic Yellow 2 and C.I. Basic Blue 3 Dyes.

Treatment of wastewaters containing hazardous substances such as dyes from the textile, paper, plastic and food industries is of great importance. Efficient technique for the removal of highly toxic organic dyes is adsorption. In this paper, adsorptive properties of the carbon-silica composite (C/SiO2) were evaluated for the cationic dyes C.I. Basic Blue 3 (BB3) and C.I. Basic Yellow 2 (BY2). The sorption capacities were determined as a function of temperature (924.6–1295.9 mg/g for BB3 and 716.3-733.2 mg/g for BY2 at 20–60 °C) using the batch method, and the Langmuir, Freundlich and Temkin isotherm models were applied for the equilibrium data evaluation using linear and non-linear regression. The rate of dye adsorption from the 100 mg/L solution was very fast, after 5 min. of phase contact time 98% of BB3 and 86% of BY2 was removed by C/SiO2. Presence of the anionic (SDS), cationic (CTAB) and non-ionic (Triton X-100) surfactants in the amount of 0.25 g/L caused decrease in BB3 and BY2 uptake. The electrokinetic studies, including determination of the solid surface charge density and zeta potential of the composite suspensions in single and mixed adsorbate systems, were also performed. It was shown that presence of adsorption layers changes the structure of the electrical double layer formed on the solid surface, based on the evidence of changes in ionic composition of both surface layer and the slipping plane area. The greatest differences between suspension with and without adsorbates was obtained in the mixed dye + SDS systems; the main reason for this is the formation of dye-surfactant complexes in the solution and their adsorption at the interface.

Adsorption equilibrium and dynamic surface tension of alkyl polyglucosides and their mixed surfactant systems with CTAB and SDS in the surface of aqueous solutions

The surface adsorption equilibrium and dynamic surface tension (DST) of alkyl polyglucosides (APGs) with single or mixed carbon chains (C8G1.46, C10G1.54, C12G1.46, C8/10G1.31 and C12/14G1.43), and of the mixed surfactant systems C8G1.46-CTAB and C8G1.46-SDS in aqueous solutions were studied. The magnitude in descending order for cmc and γcmc values of various APGs were C8G1 > C10G1 > C12G1 and C8/10G1.31 > C12/14G1.43. Both the APGs with single carbon chain and the APGs with mixed carbon chains, have approximately the same Γm and Amin values.When the concentration of APG is relatively small, the adsorption is controlled by diffusion. When APG concentrations increase, the adsorption mechanism changes from diffusion controlled into barrier controlled.The apparent diffusion coefficient (Da) decreases with an increase in APG concentrations. And the Da values of various APGs at the same concentration in descending order of magnitude is C8G1.46 > C10G1.54 > C12G1.46 and C8/10G1.31 > C12/14G1.43. The magnitude in descending order for the adsorption barrier values (Ea) of different APG products was C8G1.46 > C10G1.54 > C8/10G1.31 > C12/14G1.43 > C12G1.46. The longer the carbon chain of the APG molecules, the smaller the repulsive force of the APG molecules on the surface, and the faster the DST drops.In the C8G1.46-CTAB mixed system, when CTAB has relatively small concentration, adding C8G1.46 to CTAB solution will result in significantly lowered DST values. But when CTAB concentration is relatively large, adding C8G1.46 to CTAB solution will not result in significant change to the DST curves. The DST values of the C8G1.46-SDS mixed system is significantly lower than the single C8G1.46 and single SDS systems.

Improving stability of concentrated coal–water slurry using mixture of a natural and synthetic surfactants

The use of a surfactant mixture of natural and synthetic surfactants as additives in stabilizing coal-water slurry (CWS) formed from low rank Indian coals has been explored. The surface activities of the synthetic surfactants, hexadecyltrimethyl ammonium bromide (CTAB, cationic surfactant) and sodium dodecyl sulphate (SDS, anionic surfactant) are found to alter when various concentrations of natural surfactant, saponin (non-ionic surfactant) extracted from the fruits of Sapindous laurifolia are added to them independently. A considerable decrease in viscosity of CWS has been observed on the addition of saponin to the synthetic surfactants, CTAB/SDS (at 50:50 (w/w) for saponin:CTAB; 60:40 (w/w) for saponin:SDS systems). The mixture of anionic-nonionic is however, found to be more effective than the mixture of cationic-nonionic surfactants in reducing the apparent viscosity of the mixtures. The surface tension and contact angle data of the mixtures in solution suggest the high surface activity of the mixtures at these ratios. The rheological behaviors of CWS at weight concentrations varying from 55% to 65%wt.%, the static stability test, effect of pH, temperature, etc. have been studied. The slurries follow Bingham plastic behavior within these ranges of concentrations. A qualitative model of interaction of additive with a coal particle at the interface has been suggested.

Optimal Control for a Family of Systems in Novel State Derivative Space Form with Experiment in a Double Inverted Pendulum System

Optimal control for a family of systems in novel state derivative space form, abbreviated as SDS systems in this study, is proposed. The first step in deriving optimal control laws for SDS systems is to form an augmented cost functional. It turns out that novel differential Lagrange multipliers must be used to adjoin SDS system constraints (namely, the dynamical equations of the control system) to the integrand of the original cost functional which is a function of state derivatives. This not only eases our derivation but also makes our derivation parallel to that for systems in standard state space form. We will show via a real electric circuit that optimal control for a class of descriptor systems with impulse modes can easily be carried out using our design method. It will be shown that linear quadratic regulator (LQR) design for linear time-invariant SDS systems using state derivative feedback can be obtained via an algebraic Riccati equation. Furthermore, this optimal state derivative feedback may also be implemented using an equivalent state feedback. This is useful in real situations when only states but not the state derivatives are available for measurement. The LQR design for a double inverted pendulum system is implemented to illustrate the use of our method.

Effect of Molecular Weight on the Interfacial Dilational Viscoelasticity of Anionic Polyelectrolyte/Surfactant Systems

In this article, the effect of molecular weight on the interfacial tension and interfacial dilational viscoelasticity of polystyrene sulfonate/surfactant adsorption films at the water-octane interface have been studied by spinning drop method and oscillating barriers method respectively. The experimental results show that different interfacial behaviors can be observed in different type of polyelectrolyte/surfactant systems. PSS/cationic surfactant CTAB systems show the classical behavior of oppositely charged polyelectrolyte/surfactant systems and can be well explained by electrostatic interaction. Molecular weight of PSS plays a crucial role in the nature of adsorption film. The complex formed by CTAB and higher molecular weight PSS, which has larger dimension and stronger interaction, results in higher dilational modulus at lower surfactant bulk concentration. In the case of PSS/anionic surfactant SDS systems, the co-adsorption of PSS at interface through hydrophobic interaction with alkyl chain of SDS leads to the increase of interfacial tension and the decrease of dilational modulus at lower surfactant bulk concentration. For PSS/nonionic surfactant T × 100 systems, PSS may form a sublayer contiguous to the aqueous phase, which has little effect on interfacial tension but slightly decreases dilational modulus.

Zn(II)-Catalyzed Desymmetrization of meso-Epoxides by Aromatic Amines in Water

The Zn(OTf)2-SDS-bipyridine 1 system has proved to be an effective catalyst in water for the desymmetrization of epoxides 2a-d by anilines 3a-d. After obtaining comparable results by using Sc(III)-SDS and Zn(II)-SDS systems in the case of 2a and 3a, we have explored the enantioselective ring opening of small epoxides for which water has never been used as reaction medium. Up to date the 85% ee obtained in the case of cyclohexene oxide 2b with amines 3a and 3d are very good results and are the highest values obtained in water as reaction medium.

The Effect of Changing the Microstructure of a Microemulsion on Chemical Reactivity

A kinetic study was carried out on various solvolytic reactions in water/ NH4OT /isooctane microemulsions. The NH4OT surfactant is a derivative of the sodium salt of bis(2-ethylhexyl) sulfosuccinate (NaOT or AOT), where the Na+ counterion has been replaced by NH4+. The counterion substitution effects the phase diagram of the system, and therefore, NH4OT-based microemulsions with high water content reaching values of W = 350 (W = [H2O]/[NH4OT]) can be obtained. The presence of high W values suggests a transition in the microemulsion microstructure from water-in-oil (w/o) to oil-in-water (o/w), as was confirmed by conductivity and 1H NMR self-diffusion measurements. The interpretation of the kinetic studies in terms of pseudophase formalism allows us to analyze the effect of the microemulsion on chemical reactivity, regardless of its microstructure. It has been confirmed that the values of the solvolytic rate constants at the interphase of oil-in-water microemulsions are similar to those obtained for aqueous SDS systems, showing that the hydration degree of the interphase of the oil-in-water microemulsions is independent of W. The influence of the surfactant counterion on the solvolytic rate constants was analyzed by comparing HOT-, NaOT-, and NH4OT-based microemulsions. An important influence on the rate constants caused by the changes in the structural properties of water has been observed as was confirmed by the water 1H NMR signals.

β-Blockers and benzodiazepines location in SDS and bile salt micellar systems: An ESR study

The work here described aimed to find out the location of the different species of two families of pharmaceutical substances, namely two β-blockers (atenolol and nadolol) and two benzodiazepines (midazolam and nitrazepam) in synthetic (sodium dodecyl sulphate, SDS) and natural (bile salts-sodium cholate and sodium deoxycholate) micellar aggregate solutions. Electronic spin resonance spectroscopy studies were carried out, at 25°C and at an ionic strength of 0.10M in NaCl, using 5-, 12- and 16-doxylstearic acid probes (AS). The immobilization degree of solubilized stearic acid spin probes was found to vary with the position of the nitroxide group in the sequence 5-doxylstearic acid>12-doxylstearic acid>16-doxylstearic acid for SDS and 12-doxylstearic acid>5-doxylstearic acid>16-doxylstearic acid for both bile salts investigated. Therefore, from the rotational correlational time values obtained, it can be inferred that the structure of bile salt micelles is markedly different from that of SDS micelles and the results suggest that the bile salt micelles studied have similar structure independently of differences in the molecular structure of the respective bile salts.Drug location studies were performed at pH 4.0 (SDS solutions) or 7.0 (bile salt solutions) and 10.8 in order to study the effect of the drug ionisation on its relative position on micelles. The results have shown that drug location is controlled by the (i) drug hydrophilicity and acid/base properties, with the more soluble compound in water (atenolol) exhibiting smaller variation of rotational correlational time (in SDS and bile salts solutions), and with both β-blockers exhibiting smaller deviations in the protonated forms and (ii) the bile salt monomers, with the dihydroxylic bile salt (deoxycholate) producing larger differences.The work described herein allow us to conclude that the (protonated) β-blockers are probably located on the surface of the detergent micelles, and linked to them by means of essentially electrostatic forces, while the (neutral) benzodiazepines are probably located deeper in the interior of the micelles.

Impact of Phenolic Antioxidants on Structural Properties of Micellar Solutions

Antioxidants solubilized in micellar solutions can change micellar properties like the size and shape of micelles, critical micellar concentration (cmc) and viscosity. Interactions arising between antioxidants and the surfactant determine the locations of antioxidants and vice versa. The location and interaction are dependent on the type of both the antioxidant and surfactant. Influences of various antioxidants on the physical and structural properties were tested in micellar systems of cationic CTAB, non-ionic Brij 58 and anionic SDS. The antioxidants used to investigate the effects of gradually increasing lipophilicity were gallic acid (GA) and the gallate esters from methyl to octyl gallate (MG-OG). Hydroxy cinnamic acids (HCAs) like \(p\)-coumaric acid (pC), caffeic acid (CA), ferulic acid (FA) and sinapic acid (SA) were employed to observe effects of functional groups like hydroxyl and methoxy groups. Micellar size and shape determined by small angle neutron scattering (SANS), viscosity and cmc were chosen to characterize the antioxidant influence. In Brij 58 systems propyl gallate (PG) did not affect the cmc or aggregation number but decreased micellar size slightly due to an intercalation of PG into the region of the polyoxyethylene chain and the first adjacent alkyl chain methylene groups. In SDS systems the micellar size and cmc decreased in the presence of PG. This was attributed to PG residing in the Stern layer. However, in CTAB systems micelles swelled at low PG concentration and in the presence of GA, while higher PG concentrations and more lipophilic antioxidants led to a sphere-to-rod transition with a simultaneous increase in viscosity and decrease in cmc. This revealed the intercalation of antioxidants in the palisade layer of CTAB micelles entering into strong interactions of electrostatic and hydrophobic origin. It could be demonstrated that the interactions became stronger the more lipophil an antioxidant is and the more hydroxyl groups are attached to the aromatic ring. Differences in the location and interaction of antioxidant and micelles are proposed as being responsible for the effectiveness of antioxidants.

Phase Behavior and Phase Structure of Protein–Surfactant–Water Systems

Phase behavior of oppositely charged ovalbumin–DOTAC and BSA–DOTAC, and similarly charged ovalbumin–SDS, BSA–SDS, lysozyme–DOTAC, and BLG–SDS systems within the concentration range of 20 wt% of both protein and surfactant are examined in water. Aqueous solutions of ovalbumin yield, in succession, precipitation, gel, and solution with increased addition of the surfactant dodecyltrimethylammonium chloride (DOTAC). The stability range of each region is determined. Both isotropic and anisotropic gels are detected. Solutions of bovine serum albumin (BSA) form only a solution phase with oppositely charged DOTAC. One solution phase is also obtained with all similarly charged protein–surfactant systems except the BLG–SDS–water system, which produces a gel phase in addition to a large solution phase. 2H NMR longitudinal (R1) and transverse (R2) relaxation rates are determined in solution and gel by following the behavior of selectively deuterated surfactant at the α-methylene group next to the surfactant head group for the oppositely charged systems ovalbumin–DOTAC and BSA–DOTAC. Large R2-values proved the existence of large protein–surfactant aggregates in both systems.

The interactions of neuropeptides with membrane model systems: a case study.

The interactions between the positively charged neuropeptides substance P (SP), bradykinin (BK), and zwitterionic Met-enkephalin (ME) neuropeptides, and negatively charged SDS and zwitterionic lysophosphatidylcholine (LPC) membrane model systems, have been investigated using one- and two-dimensional nmr experiments. Proton longitudinal relaxation studies were used to characterize these interactions as intrinsic or extrinsic. An extrinsic interaction are similar to those observed for extrinsic membrane proteins. An intrinsic interaction are similar to those observed for intrinsic membrane proteins, and would require that the hydrophobic residues penetrate or insert into the hydrophobic core of the membrane. The interactions between both SP and BK and SDS, based on nmr results, may be characterized as intrinsic, and the interaction between ME and SDS may be characterized as extrinsic. Two-dimensional nuclear Overhauser enhancement spectroscopy experiments proved the insertion of the phenylalanine residues on both SP and BK into the hydrophobic core of SDS micelles. The interaction between SP and BK with LPC based on nmr results are characterized as extrinsic, with the interaction between ME and SDS characterized as weakly intrinsic.

Electron spin resonance and electron spin echo modulation of n-doxylstearic acid and N,N,N',N'-tetramethylbenzidine photoionization in sodium versus lithium dodecylsulfate micellar solutions: effect of 15-crown-5 and 18-crown-6 ether addition

Electron spin echo modulation and electron spin resonance spectra of photogenerated N,N,N',N'-tetramethylbenzidine (TMB) cation radical and n-doxylstearic acids (n-DSA) in frozen micellar solutions of sodium and lithium dodecyl sulfate containing 15-crown-5 and 18-crown-6 ethers in D/sub 2/O have been studied as a function of crown ether concentration. Modulation effects due to N-DSA with water deuteriums give direct evidence that both crown ethers are mainly located at the micellar interface and that this causes a decrease of the hydration of the micellar interface. Crown ether complexation constants for sodium and lithium micellar counterions are reported and show that 18-crown-6 > 15-crown-5 for sodium counterion and 15-crown-5 > 18-crown-6 for lithium counterion. Modulation effects from TMB/sup +/ interaction with water deuteriums indicate that the TMB molecule moves toward the micelle interfacial region when sodium or lithium cations are complexed by crown ethers. The TMB/sup +/ yield upon TMB photoionization increases by about 10% with crown ether addition for SDS and LDS micellar systems, but it is greater if the absolute values for the LDS system are compared to those for the SDS micellar system. This behavior correlates with the strength of TMB/sup +/-water interactions and suggests that the main factor in themore » photoionization efficiency is the photocation-water interaction.« less

Chromosomal proteins of Arabidopsis thaliana

In plants with large genomes, each of the classes of the histones (H1, H2A, H2B, H3 and H4) are not unique polypeptides, but rather families of closely related proteins that are called histone variants. The small genome and preponderance of single-copy DNA in Arabidopsis thaliana has led us to ask if this plant has such families of histone variants. We have thus isolated histones from Arabidopsis and analyzed them on four polyacrylamide gel electrophoretic systems: an SDS system; an acetic acid-urea system; a Triton transverse gradient system; and a two-dimensional system combining SDS and Triton-acetic acid-urea systems. This approach has allowed us to identify all four of the nucleosomal core histones in Arabidopsis and to establish the existence of a set of H2A and H2B variants. Arabidopsis has at least four H2A variants and three H2B variants of distinct molecular weights as assessed by electrophoretic mobility on SDS-polyacrylamide gels. Thus, Arabidopsis displays a diversity in these histones similar to the diversity displayed by plants with larger genomes such as wheat.The high mobility group (HMG) non-histone chromatin proteins have attracted considerable attention because of the evidence implicating them as structural proteins of transcriptionally active chromatin. We have isolated a group of non-histone chromatin proteins from Arabidopsis that meet the operational criteria to be classed as HMG proteins and that cross-react with antisera to HMG proteins of wheat.

Fluorescent monitoring of SDS gel electrophoresis

Reaction of proteins with dansyl chloride in mildly alkaline SDS systems at high mole ratios of dansyl chloride to protein yields dansylated proteins that can be run in SDS gel electrophoresis systems with no significant change in protein mobility. The procedure is simple