Pure SDS Research Articles

Novel core–shell and recyclable gas hydrate promoter for efficient solidified natural gas storage

The storage and transportation of gases, including hydrogen, methane, and carbon dioxide in the form of gas hydrates, have recently garnered considerable attention. The practical implementation of gas hydrates crucially depends on the development of efficient and reusable promoters. In this study, novel core–shell magnetic nanoparticles (CSNs) developed as recyclable promoter to enhance gas uptake. Hydrate formation experiments indicated that the storage capacity can reach up to 132.7 ± 1.4 v/v and 160.6 ± 2.5 v/v in CSNs and CSNs + SDS solutions, respectively. Compared to pure water and SDS solution, the initial methane consumption rate (0.5972 mol/h) of CSNs increased by 12.2 times and 1.08 times at 3000 ppm, respectively. CSNs exhibited favorable characteristics in terms of cycling ability and preventing foam formation during repeated methane hydrate formation and dissociation experiments. Furthermore, the combination of CSNs and SDS resulted in a 72 % reduction in hydrate nucleation induction time and a 58.3 % decrease in foam formation ability compared to the sole use of SDS. In comparison to pure water, the addition of CSNs increased the onset temperature of hydrate formation by 4 °C and reduced the driving force required for methane hydrate formation. Additionally, molecular dynamics simulation studies revealed that CSNs effectively improved the amount of the ordered water structure, hydrate cage formation, and the growth state of methane hydrates. These properties make CSNs promising for potential use in the storage and transportation of gas, considering the economic and environmental advantages associated with the use of promoters.

Carbon nanotubes-based porous media constructed via 3D printing for methane hydrate formation

Utilizing porous materials (e.g., activated carbon) as a fixed bed has been established as an effective method for promoting methane hydrate formation. However, hydrate growth typically leads to significant volume expansion within the fixed bed, resulting in reduced apparent hydrate density. In this study, 3D printing with carbon nanotubes (CNTs) as substrates was employed to create porous media specifically designed for methane hydrate formation. This approach enabled precise control over the size and structure of the media, as well as the ability to achieve pores of varying scales and porosities. As fixed beds, these porous media provided ample pore space (particularly millimeter-sized pores) for methane hydrate growth, leading to compact agglomeration of hydrates and a substantial increase in the apparent methane storage capacity, which is increased from approximately 60 v/v in a pure SDS solution system to 90–100 v/v in the porous medium. Furthermore, unlike traditional activated carbon, which typically undergoes volume expansion during hydrate growth, the porous media developed in this study avoided any volume expansion due to their unique one-piece design and pre-engineered pore structures. This research presents a novel approach to constructing gas hydrate fixed beds, offering significant potential for application in hydrate-based energy storage technologies.

Spectroscopic and tensiometric considerations on anionic surfactants (SDS) and ascorbic acid/ascorbates interactions

The cosmetics and personal care products market is developing dynamically and the formulations of products are subject to numerous modifications due to consumer expectations and market trends. An increase in demand for products containing ascorbic acid or its more stable forms has been observed for several years. In this study, the correlation between SDS and ascorbic acid or its derivatives in aqueous solutions was assessed using spectroscopic and tensiometric methods. The influence of SDS interactions on the total antioxidant capacity of ascorbic acid/ascorbic acid derivatives was analyzed. The highest FRAP values of SDS-AA2G and SDS-EAC systems (0.17 and 2.71 mmol Fe2+/g, respectively) were at SDS concentration of 0.40 mM and were much higher than the ones of pure ascorbic acid derivatives. Based on the surface tension isotherms and Szyszkowski's equation, it was found that for the tested SDS/ascorbic acid, ascorbyl glucoside and 3-O-ethyl ascorbic acid systems, the CMC values were: 3.85, 2.54 and 3.31 mmol/dm3. There was also an influence on the values of the adsorption parameters, i.e. the surface excess at the saturated interface, the minimum molecular area in the adsorption layer at the saturated interface and the Gibbs free energy of adsorption. Moreover, in most of the analyzed cases, the tested systems had better wetting properties, which resulted in lower values of the contact angle than in the case of pure SDS solution.

Experimental Investigation of Effect on Hydrate Formation in Spray Reactor

The effects of reaction condition on hydrate formation were conducted in spray reactor. The temperature, pressure, and gas volume of reaction on hydrate formation were measured in pure water and SDS solutions at different temperature and pressure with a high-pressure experimental rig for hydrate formation. The experimental data and result reveal that additives could improve the hydrate formation rate and gas storage capacity. Temperature and pressure can restrict the hydrate formation. Lower temperature and higher pressure can promote hydrate formation, but they can increase production cost. So these factors should be considered synthetically. The investigation will promote the advance of gas storage technology in hydrates.

Sodium dodecyl sulfate-ethoxylated polyethylenimine adsorption at the air-water interface: how the nature of ethoxylation affects the pattern of adsorption.

The strong interaction between ionic surfactants and polyelectrolytes of opposite charge results in enhanced surface adsorption at the air-water interface down to low surfactant concentrations and in some cases in the formation of ordered surface structures. A notable example which exhibits such properties is the mixture of polyethylenimine, PEI, and sodium dodecyl sulfate, SDS. However, the electrostatic interaction, around charge neutralization, between the surfactant and polymer often results in precipitation or coacervation. This can be mitigated for PEI-surfactant mixtures by ethoxylation of the PEI, but this can also result in a weaker surface interaction and a significant reduction in the adsorption. It is shown here that by localizing the ethoxylation of the PEI into discrete regions of the polymer precipitation upon the addition of SDS is suppressed, the strong surface interaction and enhanced adsorption of the polymer-surfactant mixture is retained. The adsorption of SDS in the presence of ethoxylated PEI is greatly enhanced at low SDS concentrations compared to the adsorption for pure SDS. The adsorption is equally pronounced at pH 7 and 10 and is largely independent of the degree of ethoxylation. Surface ordering, more than monolayer adsorption, is observed over a relatively narrow range of SDS concentrations and is most pronounced at pH 10 and for the polymers with the lower degree of ethoxylation. The results show that ethoxylated PEI's reported here provide a suitable route to enhanced surfactant adsorption while retaining favorable solution properties in which precipitation effects are minimized.

Simultaneous removal of cadmium ions and phenol with MEUF using SDS and mixed surfactants

Micellar-enhanced ultrafiltration (MEUF) is a promising technology to remove metal ions and organic contaminants simultaneously from wastewater. A laboratory experiment was conducted to evaluate the efficiency of a MEUF operation for the removal of Cd2+ and phenol using pure SDS and mixed surfactants (Triton X-100/SDS). In pure SDS system, with the increase of the feed SDS concentration, a significant rise in Cd2+ rejection was obtained, which peaked at 97.0% with initial SDS concentration being 8.0mM. Nevertheless, the phenol rejections only kept moderately increasing from 14.5% to 40.0%. In mixed Triton X-100/SDS system, the rejections of Cd2+ and phenol were both enhanced by the moderate addition of nonionic surfactant for the same total feed surfactant concentration as the pure SDS system. With the increase of the molar ratios of Triton X-100 to SDS (α), Cd2+ rejection increased slightly with α ranging from 0 to 0.8, and peaked at 91.3%. And the phenol rejection kept increasing from 27.7% to 42.4% when α was less than 1.0 followed by slight decrease to 40.2% at α=1.5. Moreover, the SDS dosage and the surfactant(s) concentration in permeate were reduced efficiently. The permeate flux of MEUF with mixed surfactants was lower than that with pure SDS.

Solvation dynamics of Coumarin 153 in SDS dispersed single walled carbon nanotubes (SWNTs)

We have studied the solvation dynamics and rotational relaxation of Coumarin 153 (C-153) in SDS dispersed two different types of single walled carbon nanotubes (SWNTs), namely metallic and semiconducting, using picosecond fluorescence spectroscopy. It has been observed that solvation dynamics of C-153 in SWNTs is severely retarded compared to pure water and SDS micelle. Time resolved fluorescence anisotropy study suggests that C-153 molecules are located on the surface of SWNT, where the rotational motion of the probe is severely hindered compared to SDS micelle due to the restriction imposed by SWNT surface as well as surrounding SDS monomers or SDS half-cylindrical micelles adsorbed on SWNT surface.

Experimental study on micellar-enhanced ultrafiltration (MEUF) of aqueous solution and wastewater containing lead ion with mixed surfactants

We studied the performance of single and mixed surfactants for removal of Pb 2+ from aqueous solution and wastewater by MEUF. Anionic surfactant, SDS and 2 nonionic surfactants, TX-100 and NP12 were used. The experiments were carried out using a flat sheet module with polyethersulfone membrane (MWCO 10 kDa). Single surfactants, SDS gave high Pb 2+ rejections but low SDS rejections while TX-100 and NP12 showed opposite results. The use of mixed surfactants between SDS and nonionic surfactants can effectively enhance both Pb 2+ and surfactant rejections. The optimum amount of nonionic surfactants added was at mole fractions of 0.1 for both SDS/TX-100 and SDS/NP12 systems in which the highest Pb 2+ rejection can be achieved. At this mole fraction (1.37 mM) of TX-100 and NP12 with 12.3 mM of SDS, the Pb 2+ rejections were higher than 98.4%. High rejections of SDS (80%), TX-100 and NP12 (> 99%) were also obtained. The MEUF showed promising results of real wastewater tested. The analysis of transport resistances showed that polarization resistance was dominant and fouling was very low for both single and mixed surfactants. Fouling resistances of mixed surfactants were higher than that of pure SDS but lower than those of pure nonionic surfactants.

Membrane charge dependent states of the β-amyloid fragment Aβ (16–35) with differently charged micelle aggregates

A β (16–35) is the hydrophobic central core of β-amyloid peptide, the main component of plaques found in the brain tissue of Alzheimer's disease patients. Depending on the conditions present, β-amyloid peptides undergo a conformational transition from random coil or α-helical monomers, to highly toxic β-sheet oligomers and aggregate fibrils. The behavior of β-amyloid peptide at plasma membrane level has been extensively investigated, and membrane charge has been proved to be a key factor modulating its conformational properties. In the present work we probed the conformational behavior of A β (16–35) in response to negative charge modifications of the micelle surface. CD and NMR conformational analyses were performed in negatively charged pure SDS micelles and in zwitterionic DPC micelles “doped” with small amounts of SDS. To analyze the tendency of A β (16–35) to interact with these micellar systems, we performed EPR experiments on three spin-labeled analogues of A β (16–35), bearing the methyl 3-(2,2,5,5-tetramethyl-1-oxypyrrolinyl) methanethiolsulfonate spin label at the N-terminus, in the middle of the sequence and at the C-terminus, respectively. Our conformational data show that, by varying the negative charge of the membrane, A β (16–35) undergoes a conformational transition from a soluble helical–kink–helical structure, to a U-turn shaped conformation that resembles protofibril models.

Laser flash photolysis and time-resolved fluorescence measurements of the aggregation number of SDS–biopolymer complexes

Aqueous solutions of 0.5% sodium carboxymethyl cellulose, NaCMC, and 2-hydroxyethyl cellulose, HEC, and variable concentration of sodium dodecyl sulfate, SDS, were studied by the intensities ratio of pyrene fluorescence bands (I/III and monomer/excimer) and conductance measurements to determine the critical aggregation concentration, cac, and the degree of micellar dissociation, α, respectively. The cac of these systems is close to 2–4 × 10 −3 M and values of α are consistent with the formation of SDS micelles adsorbed cooperatively to the polymer backbone. Laser flash photolysis (LFP) and time-resolved fluorescence (TRF) techniques were employed to determine the micellar aggregation number, N, using the probes flavone and pyrene, respectively. The obtained N for HEC/SDS and NaCMC/SDS were 48 and 68, respectively. The presence of the counterions at the NaCMC backbone is the main factor responsible for this number. Besides, the transient spectra of flavone and present in 0.5% HEC or NaCMC with and in absence of SDS are discussed. Flavone triplet state exit rate constant from the biopolymer/SDS complexes showed that these systems are completely different from a pure SDS micelle.

Adsorption kinetics of surfactant mixtures from micellar solutions as studied by maximum bubble pressure technique

The adsorption kinetics of micellar solutions of anionic/cationic SDS/DATB mixtures with mixing ratios of 10/1 and 10/2, respectively, are studied experimentally by means of the maximum bubble pressure method. For long adsorption times the adsorption of the highly surface-active anionic/cationic complex leads to a decrease of dynamic surface tension in comparison to the single SDS system. However, the situation is the reverse for short adsorption times where the dynamic surface tension is increased by addition of the cationic surfactant, although the overall concentration is increased. This unexpected behavior is explained by partial solubilization of free SDS molecules into micelles formed by SDS/DTAB complexes. With increasing overall concentration, when eventually the CMC of SDS is reached, the anionic/cationic complex itself is solubilized by SDS micelles. Finally, no complex micelles, which for their part can solubilize an excess of SDS molecules, are present. Hence, the dynamic properties of the solution are no longer influenced by the depletion of SDS molecules and the mixture tends to behave like a pure SDS solution.

Surfactant-induced retardation of the thermocapillary flow at a gas/liquid interface

Systematic study of soluble surfactant effect on thermocapillary flow that artificially provoked by a steady point heat source at a gas/liquid interface was performed experimentally. Surface velocity and temperature profiles were measured at three Δ Ts (temperature difference between heated source and bulk solution) for pure water and SDS solutions of five concentrations. Experimental results show that small amounts of SDS in water retard significantly the thermocapillary flow and consequently alter the surface velocity and temperature profiles. The dependence of the average interfacial Reynolds number ratio, Re s / Re w, and average temperature difference ratio, ( Θ S - Θ C )/( Θ W - Θ C ), on ΔT and C can be satisfactorily represented by proposed empirical correlations. Moreover, mechanism of retardation by surfactant for thermocapillary and diffusocapillary flows is found to be quite different. While surfactant-induced retardation of the thermocapillary flow is due to the interfacial elasticity property of surfactant solutions, that of the diffusocapillary, on the other hand, is mainly due to the reduction in the driving force that triggers the diffusocapillary flow.

A Spin-Probe Study of the Modification of the Hydration of SDS Micelles by Insertion of Sugar-Based Nonionic Surfactant Molecules

The spin-probe detected polarity index H(25 °C) of SDS micelles decreases linearly with the number of inserted sugar-based nonionic surfactant molecules. This decrease is interpreted as being due to the expulsion of water molecules by the sugar groups from the polar shell surrounding the hydrocarbon core of the dodecyl micelle. Employing the geometrical model described in the companion paper immediately preceding this work, the effective volume of water expulsion is found to be similar to the volume of the sugar groups after taking into account that the OH bonds of the sugar groups also contribute to the polarity index H(25 °C). The estimate of the hydration of pure SDS micelles as a function of their aggregation number from these studies with the spin probe 16 doxylstearic acid methyl ester is similar to that with 5 doxylstearic acid methyl ester. This confirms that both spin probes are located similarly in the polar shell.

Analysis of Protein-Mixed Surfactant System Interactions ;

The denaturation of bovine serum albumin (BSA) by mixed surfactant systems was studied by examining surfactant adsorption on BSA. Polyoxyethylenealkylether (alcohol ethoxylate : AE) inhibited SDS-binding to BSA with consequent denaturation of BSA. The higher the concentration of AE or the larger the adduct number of oxyethylene (EO), the greater was the inhibitory effect of AE on SDS-induced denaturation of BSA. The adsorption of AE on an electrostatic surface significantly increased when SDS was present. The enthalpy of adsorption of the SDS-AE mixed system on BSA as determined with a microcalorimeter clearly differed from that of pure SDS or AE. The AE effect on SDS-induced BSA denaturation is thus due to the adsorption of AE on the alkyl chain of SDS electrostatically bound to BSA. The adsorption of AE apparently stabilizes the alkyl chain of SDS electrostatically bound to BSA, with a consequent decrease in the binding of SDS to BSA.

Structure of pure SDS and DTAB micelles in brine determined by small-angle neutron scattering (SANS)

The geometrical structure of pure SDS and DTAB surfactant micelles in the absence of added salt as well as its dependence on the concentration of NaBr have been investigated at 40°C using small-angle neutron scattering (SANS). In contrast to previous SANS measurements on the same systems we have analysed the scattering data in the entire regime of scattering vectors that are relevant for determining the structure of the micelles. Our obtained results for pure surfactant micelles, as well as those of mixed catanionic micelles presented in a recent study, show somewhat unexpectedly that ordinary surfactant micelles are shaped as circular or elongated bilayers (tablets). Both SDS and DTAB micelles appeared to be disk-like in pure D2O and the corresponding data were best fitted with a model for (monodisperse) oblate ellipsoids of revolution with half axes a=12.0 A, b=20.3 A ([SDS]=1.0 wt.%) and a=12.4 A, b=21.6 A ([DTAB]=1.0 wt.%). The half axis b related to the disk radius increases in both cases with an increasing amount of added salt to about 23 A (SDS) and 24 A (DTAB) at [NaBr]=0.1 M and at about [NaBr]=0.2 M the SDS micelles become tablet-shaped, i.e. tri-axial ellipsoids with half axes a<b<c. For DTAB micelles the disk-to-tablet transition occurs between [NaBr]=0.5 and 0.7 M. As the amount of salt is further increased the micelles grow strongly with respect to length, but decrease slightly in width to about b=20 A (SDS) and b=22 A (DTAB) at [NaBr]=1.0 M. Half the thickness of the micelles varies only slightly with the solution state and is found to be about 75–90% of the fully extended hydrocarbon chain (=16.7 A). Hence, all elongated micelles appeared to have an elliptical cross section with an axial ratio 1.5<b/a<1.6. At [NaBr]=0.7 M the SDS micelles are considerably elongated and polydisperse and their (volume-weighted) average length increases rapidly with surfactant concentration from about 200 A at [SDS]=0.25 wt.% to about 400 A at [SDS]=1.0 wt.%. At [NaBr]=1.0 M the SDS micelles were seen to be shaped as long flexible ribbons too long, i.e. several thousands of Angstroms, for their size distribution to be determined from our SANS data whereas DTAB micelles still were rather short, i.e. c=30 A.

The Energetics of Forming Equilibrated Bilayer Vesicles

On the basis of detailed model calculations we demonstrate that the free energy required to form an equilibrated spherical bilayer vesicle is made up of two main contributions: the (size-independent) work of bending the constituent monolayers and the work of stretching the bilayer that is determined by the planar bilayer tension. A major part of the bending free energy arises due to a reduction of the overall hydrocarbon chain volume upon forming a spherically shaped bilayer shell out of a planar monolayer, while keeping the total hydrocarbon/water contact area fixed and the chemical potentials constant. This contribution is only partially counterbalanced by a sum of contributions due to curvature-dependent molecular free energies of various origins. The overall free energy of bending a pure (charged) SDS bilayer into a vesicle is found to be quite large (∼90kT). However, admixing with a long-chain alcohol brings it down substantially and is thus crucial for spontaneous vesicle formation to occur.

Evidence for Sodium Dodecyl Sulfate/Protein Complexes Adopting a Necklace Structure

Structural analysis by cryo‐electron microscopy and small‐angle X‐ray scattering of ten sodium dodecyl sulfate/protein complexes in 25 mM Tris/HCl, 0.192 M glycine, pH 8.3, showed necklace‐like structures of spherical micelles dispersed along the unfolded peptide chain. The micelles of most SDS/protein complexes had a constant diameter (≈ 6.2nm), slightly larger than pure SDS micelles (≈ 5.7 nm), all micelles possessing a degree of surface roughness. The micelle‐associated polypeptide is mostly situated at the interface of the sulfate head groups and hydrocarbon core, intruding into the core rather than outward from the surface. Proteins with a molecular mass less than about 20 kDa formed complexes with a single SDS micelle. Multi‐micellar SDS/protein complexes had centre‐to‐centre intermicellar distances in the range 7.0–12.0 nm. Our findings on the constancy of micellar size, number of micelles/complex, and the relationship between the degree of occupancy of micelles and a polypeptide's molecular mass, have enabled us to speculate on the correlation between the electrophoretic mobility of a polypeptide in SDS/PAGE and its molecular mass. The anomalous electrophoretic behaviour observed for the sodium dodecyl sulfate/histone H5 complex is accounted for by the large micelle of its complex.

Evidence for Sodium Dodecyl Sulfate/Protein Complexes Adopting a Necklace Structure

Structural analysis by cryo-electron microscopy and small-angle X-ray scattering of ten sodium dodecyl sulfate/protein complexes in 25 mM Tris/HCl, 0.192 M glycine, pH 8.3, showed necklace-like structures of spherical micelles dispersed along the unfolded peptide chain. The micelles of most SDS/protein complexes had a constant diameter (≈ 6.2nm), slightly larger than pure SDS micelles (≈ 5.7 nm), all micelles possessing a degree of surface roughness. The micelle-associated polypeptide is mostly situated at the interface of the sulfate head groups and hydrocarbon core, intruding into the core rather than outward from the surface. Proteins with a molecular mass less than about 20 kDa formed complexes with a single SDS micelle. Multi-micellar SDS/protein complexes had centre-to-centre intermicellar distances in the range 7.0–12.0 nm. Our findings on the constancy of micellar size, number of micelles/complex, and the relationship between the degree of occupancy of micelles and a polypeptide's molecular mass, have enabled us to speculate on the correlation between the electrophoretic mobility of a polypeptide in SDS/PAGE and its molecular mass. The anomalous electrophoretic behaviour observed for the sodium dodecyl sulfate/histone H5 complex is accounted for by the large micelle of its complex.

Evidence for Sodium Dodecyl Sulfate/Protein Complexes Adopting a Necklace Structure

Structural analysis by cryo-electron microscopy and small-angle X-ray scattering of ten sodium dodecyl sulfate/protein complexes in 25 mM Tris/HCl, 0.192 M glycine, pH 8.3, showed necklace-like structures of spherical micelles dispersed along the unfolded peptide chain. The micelles of most SDS/protein complexes had a constant diameter (approximately 6.2 nm), slightly larger than pure SDS micelles (approximately 5.7 nm), all micelles possessing a degree of surface roughness. The micelle-associated polypeptide is mostly situated at the interface of the sulfate head groups and hydrocarbon core, intruding into the core rather than outward from the surface. Proteins with a molecular mass less than about 20 kDa formed complexes with a single SDS micelle. Multi-micellar SDS/protein complexes had centre-to-centre intermicellar distances in the range 7.0-12.0 nm. Our findings on the constancy of micellar size, number of micelles/complex, and the relationship between the degree of occupancy of micelles and a polypeptide's molecular mass, have enabled us to speculate on the correlation between the electrophoretic mobility of a polypeptide in SDS/PAGE and its molecular mass. The anomalous electrophoretic behaviour observed for the sodium dodecyl sulfate/histone H5 complex is accounted for by the large micelle of its complex.

The concentration dependence of adsorption from a mixture of β-lactoglobulin and sodium dodecyl sulfate onto methylated silica surfaces

The adsorption from a mixture of SDS and β-Lactoglobulin, 1:5 ( w w ), onto a methylated silica surface was studied in situ by ellipsometry. The amounts adsorbed from different concentrations of the mixture, at pH 7, were compared with those adsorbed from the corresponding pure SDS and β-lactoglobulin solutions. At high concentrations of the mixture, where the CMC of SDS is approached or exceeded, the adsorbate was probably dominated by SDS, indicated by similar kinetics and amounts adsorbed as for SDS solution alone. The amount adsorbed increased, in this concentration range, when the system was rinsed with buffer solution. This was probably due to an exchange between SDS and β-lactoglobulin when the system was diluted. At intermediate concentrations of SDS and β-lactoglobulin, the amounts adsorbed from the mixtures increased and reached a maximum. This maximum was observed both before and after rinsing. Before rinsing the adsorbate might have been a mixture of SDS and β-lactoglobulin while after rinsing probably only β-lactoglobulin remained. At low concentrations, larger amounts were adsorbed from the mixture than from β-lactoglobulin solution alone. In this concentration range rinsing caused minor desorption, indicating that SDS is co-adsorbed with the protein, even in those cases were no adsorption from a pure SDS solution was seen. This indicated that the binding of SDS to β-lactoglobulin at low concentrations is stronger than to the silica surface and that this binding facilitated the adsorption of protein.