Aqueous Solutions Of Sodium Dodecyl Sulfate Research Articles

Three-dimensional internal flow evolution of an evaporating droplet and its role in particle deposition pattern

The internal flow within an evaporating sessile droplet is one of the driving mechanisms that lead to various particle deposition patterns seen in applications such as inkjet printing, surface patterning, and blood stain analysis. Despite decades of research, the causal link between droplet internal flow and particle deposition patterns has not been fully established. In this study, we employ a three-dimensional (3D) imaging technique based on digital inline holography to quantitatively assess the evolution of internal flow fields and particle migration in three distinct types of wetting droplets, namely water droplets, sucrose aqueous solution droplets, and sodium dodecylsulfate aqueous solution droplets, throughout their entire evaporation process. Our imaging reveals the three-stage evolution of the 3D internal flow regimes driven by changes in the relative importance of capillary flow, Marangoni flow, and droplet boundary movement during evaporation. Moreover, the migration of individual particles from their initial locations to deposition can be divided into five categories, with some particles depositing at the contact line and others inside the droplet. In particular, we observe the changing migration directions of particles due to competing Marangoni and capillary flows. We further develop an analytical model that predicts the droplet internal flow, deposition patterns, and determines the deposition mechanisms depending on their initial locations and evolving internal flow. The model, validated using different types of droplets from our experiment and the literature, can be further expanded to other Newtonian and non-Newtonian droplets, potentially serving as a real-time assessment tool for particle deposition in various applications.

Ionic liquid as a cosurfactant for critical heat flux enhancement during boiling with aqueous surfactant solutions

Surfactants are often used to improve boiling heat transfer due to the ease of their implementation. While aqueous surfactant solution significantly increases the heat transfer coefficient (HTC), it is known to deteriorate the critical heat flux (CHF) relative to the base fluid water. The high foamability of most surfactant solutions causes vapor crowding on the heater surface, making surface modification techniques ineffective for CHF enhancement. Here, we address the issue of relative degradation of CHF due to surfactant by using an ionic liquid as a cosurfactant. We employ a unique boiling fluid, where 1-ethyl-3-methylimidazolium chloride ([C2mim][Cl]), a low-foaming ionic liquid, is introduced as a co-surfactant in aqueous sodium dodecyl sulfate (SDS) solution. Motivated by the synergistic increase in foamability of the aqueous surfactant solution due to the addition of ionic liquid, we examine the boiling performance at various combinations of concentrations of the two additives in the solution. The mixture consistently exhibits higher CHF and HTC than an SDS only solution, with the best enhancement observed for a mixture of ≈ 30 ppm SDS and ≈ 750 ppm [C2mim][Cl], resulting in ≈1.6× and ≈1.5× enhancements in CHF and HTC, respectively, compared to the SDS only solution (≈ 30 ppm). We next fine-tune the concentration of cosurfactant to demonstrate an exceptionally high HTC of ≈93 kW/(m2 – ℃) with a CHF value comparable to that of pure water. Enhanced foamability and in-situ improvement in the wettability of the heater surface enhance the HTC and the CHF, respectively. This facile technique for enhancing HTC with water as the base fluid, without compromising on CHF, holds promise for high heat flux thermal management applications.

Experimental study on heat transfer performance enhancement of pulsating heat pipes induced by surfactants

Pulsating heat pipe (PHP) is considered as a promising technique to address the thermal dissipation issues in micro-electronic devices, but its heat transfer performance needs to be further enhanced urgently. In this study, the PHP comprehensive performance experimental system was established. Then, the influence of surfactant sodium dodecyl sulfate (SDS) aqueous solution on the heat transfer performance of PHP was experimentally investigated and the visualization of PHP with surfactant was also accomplished. Additionally, based on Marangoni effect and surface tension, a comprehensive analysis was conducted on the impact mechanism of surfactants on PHP. The experimental results indicated that the oscillatory disturbance of the liquid slug inside the PHP is enhanced by the addition of SDS, and the resulting pressure imbalance and temperature difference enhance the directional flow of the working fluid. Meanwhile, under the operating conditions of 30 W working thermal power and the solution concentration of 0.001 wt%, the thermal resistance of PHP was reduced by 30.7 % compared with that of deionized water (DI water). This indicated that the working fluid with low concentration SDS could increase the area of liquid film and reduce the thermal resistance, which is induced by the surface tension and Marangoni effect due to the uneven distribution of surfactants. However, the thermal resistance of PHP with the SDS concentration of 0.2 wt% is higher than that of DI. This means that high concentration of SDS would deteriorate the startup characteristics and the heat transfer performance of PHP. Therefore, high concentrations of surfactants should be avoided from practical application of PHP.

Flow-Driven Self-Propulsion of Oil Droplet on a Surfactant Solution Surface, as Observed by Time-Resolved Interfacial Tension and Surface Flow Speed Measurements.

The imbalanced force of the interfacial tension applied to an object has often been taken into account in the analysis of the motion mechanism of self-propelled systems. However, heterogeneous distributions of the interfacial tension also cause Marangoni flows, and these flows also contribute to the self-propulsion through the viscous force. The contribution of such flows has not been observed directly, while the interfacial tension difference has been measured in some systems. In this study, simultaneous measurements of the interfacial tension and surface flow speed of the unidirectional self-propelled motion of a butyl salicylate (BS) droplet in a circular channel on a sodium dodecyl sulfate (SDS) aqueous solution were achieved by the quasi-elastic laser scattering method. The droplet position was also recorded by observing its fluorescence excited by a UV light. The BS droplet speed dependence of the interfacial tension and surface flow speed were measured by varying the initial BS concentration codissolved in the SDS aqueous solution. As a result, a periodic decrease of the interfacial tension and a periodic increase of the speed of both forward and backward flows were observed when the droplet passed the sampling position of the time-resolved measurements. When they were converted to the distribution in space of the droplet position, no droplet speed dependence of the interfacial tension difference between the front and rear of the droplet was observed. On the other hand, the speed of both forward and backward flows increased as the droplet speed increased. By analysis of the above results with a simplified model, it was clarified that the forward flow driven by the interfacial tension gradient at the droplet front is actually important in the mechanism of the unidirectional self-propelled motion of a droplet.

Removal of anionic surfactant from aqueous solutions by adsorption onto biochars: characterisation, kinetics, and mechanism.

Biochar, a waste biomass-derived adsorbent, holds promise for decentralised wastewater treatment. However, limited research exists on its efficacy in adsorbing anionic surfactants in wastewater. To address this, the adsorption of sodium dodecyl sulphate (SDS), a common anionic surfactant, was studied using various biochar types: rice husk biochar (RH-550 and RH-700), wheat straw biochar (WS-550 and WS-700) produced at 550°C and 700°C, wood-based biochar (OB), and activated carbon (AC) as a control. The study investigated the impact of pH (3-9), adsorbent loading (1-10 g/L), adsorbent size (<0.5-2.5 mm), contact time (5-180 min), and initial concentration (50-200 mg/L) on SDS removal. Under optimised conditions (100 mg/L SDS, 4 g/L adsorbent, 1-2 mm particle size, pH 8.3, and 180 min contact time), maximum SDS removals were RH-550 (78%), RH-700 (82.4%), WS-550 (89.5%), WS-700 (90.4%), AC (97%), and OB (88.4%). Among the tested adsorbent materials, WS-550 exhibited the highest SDS adsorption capacity at 66.23 mg/g compared to AC (80.65 mg/g), followed by RH-550 (49.75 mg/g), OB (45.87 mg/g), RH-700 (43.67 mg/g), and WS-700 (42.74 mg/g). SDS adsorption followed a pseudo-second-order kinetic model, indicating chemisorption on the adsorbent surface. The Freundlich isotherm model exhibited a better fit for the experimental data on SDS adsorption using all tested adsorbents except for RH-550. This study showed that biochars produced from agricultural and forestry residues are effective adsorbents for SDS in aqueous solutions and can be a promising sustainable and low-cost material for the treatment of greywater containing anionic surfactants (e.g. handwashing, laundry, kitchen, and bathroom greywaters).

Counter-Ion Effect on the Surface Potential of Foam Films and Foams Stabilized by 0.5 mmol/L Sodium Dodecyl Sulfate

It is well known that the type of counter-ion affects the state of the adsorption layer of ionic surfactants and, consequently, its surface potential. Yet, it is not clear how they affect the foamability, the rate of foam decay or foam production. How is the surface potential of the air/water interface related to the properties of the foam? This work aims to answer these questions. Foam films, stabilized by 0.5 mmol/L sodium dodecyl sulfate (SDS) in the presence of added LiCl, NaCl, and KCl, were studied by means of the interferometric experimental setup of Scheludko–Exerowa. The surface potential values were derived from the equilibrium film thickness by means of the DLVO theory. A linear relation between the values of the surface potential and specific adsorption energy of the counter-ions on the air/water interface was established. The slope of this linear relation depends on the salt concentration. The foamability, the rate of foam decay, and the foam production of the same aqueous solutions of SDS and added salts were studied by means of the shaking method. A correlation was found between the derived surface potential of the foam film’s surfaces and the properties of the foam. The foam production, which is the ratio between the initial foam volume and the rate of foam decay, increases with the decrease in the surface potential. Previous studies in the literature confirm that the lower surface potential promotes higher surfactant adsorption, thus boosting more foam and vice versa. It was also confirmed that the dual effect of KCl on foam production involves converting the best foam stabilizer into a foam suppressor at the highest salt concentration.

Optimization and Enhancement of the Peroxidase-like Activity of Hemin in Aqueous Solutions of Sodium Dodecylsulfate.

Iron porphyrins play several important roles in present-day living systems and probably already existed in very early life forms. Hemin (= ferric protoporphyrin IX = ferric heme b), for example, is the prosthetic group at the active site of heme peroxidases, catalyzing the oxidation of a number of different types of reducing substrates after hemin is first oxidized by hydrogen peroxide as the oxidizing substrate of the enzyme. The active site of heme peroxidases consists of a hydrophobic pocket in which hemin is embedded noncovalently and kept in place through coordination of the iron atom to a proximal histidine side chain of the protein. It is this partially hydrophobic local environment of the enzyme which determines the efficiency with which the sequential reactions of the oxidizing and reducing substrates proceed at the active site. Free hemin, which has been separated from the protein moiety of heme peroxidases, is known to aggregate in an aqueous solution and exhibits low catalytic activity. Based on previous reports on the use of surfactant micelles to solubilize free hemin in a nonaggregated state, the peroxidase-like activity of hemin in the presence of sodium dodecyl sulfate (SDS) at concentrations below and above the critical concentration for SDS micelle formation (critical micellization concentration (cmc)) was systematically investigated. In most experiments, 3,3',5,5'-tetramethylbenzidine (TMB) was applied as a reducing substrate at pH = 7.2. The presence of SDS clearly had a positive effect on the reaction in terms of initial reaction rate and reaction yield, even at concentrations below the cmc. The highest activity correlated with the cmc value, as demonstrated for reactions at three different HEPES concentrations. The 4-(2-hydroxyethyl)-1-piperazineethanesulfonate salt (HEPES) served as a pH buffer substance and also had an accelerating effect on the reaction. At the cmc, the addition of l-histidine (l-His) resulted in a further concentration-dependent increase in the peroxidase-like activity of hemin until a maximal effect was reached at an optimal l-His concentration, probably corresponding to an ideal mono-l-His ligation to hemin. Some of the results obtained can be understood on the basis of molecular dynamics simulations, which indicated the existence of intermolecular interactions between hemin and HEPES and between hemin and SDS. Preliminary experiments with SDS/dodecanol vesicles at pH = 7.2 showed that in the presence of the vesicles, hemin exhibited similar peroxidase-like activity as in the case of SDS micelles. This supports the hypothesis that micelle- or vesicle-associated ferric or ferrous iron porphyrins may have played a role as primitive catalysts in membranous prebiotic compartment systems before cellular life emerged.

The significance of synthesized marine algae/ZnO nanoparticles for the degradation of sodium do-decyl sulphate: Response surface methodology

Sodium dodecyl sulfate (SDS) is an organic compound used in many cleaning and hygiene products. This anionic surfactant called sodium dodecyl sulphate (SDS) is easily able to enter seawater through the discharge of home and commercial wastewater. The current study look into how marine algae nanoparticles breakdown SDS surfactant under diverse environmental conditions. Additionally, the various influences on the biodegradation process are researched and analysed using Response surface methodology. SEM analysis was used to determine the particle size. Synthesised ZnO-NP's crystalline structure is amply confirmed by XRD, and FTIR reveals the various functional groups that are present. The findings of this study demonstrated how the nanoparticle will affect several parameters including optimum time of 35 min, dosage of 0.35 g/lit, pH of 9, temperature of 313 K, and initial concentration of 100 ppm of SDS in aqueous solution. With the optimum conditions, we can successfully extract SDS from aqueous solution with a 93 % removal percentage.

Effects of SDS surface-active agents on hydrodynamics and oxygen mass transfer in a square bubble column reactor: Experimental and CFD modeling study

This work examined experimentally and numerically the effects of sodium dodecyl sulfate (SDS) surfactant agent on mass transfer coefficients kLaL and kL in a high-aspect square bubble column reactor. To this end, SDS aqueous solutions at concentrations between 5 ppm and 30 ppm were prepared. Superficial gas velocity was varied from 0.74 cm.s−1 to 9.44 cm.s−1 covering all flow regimes to analyze the interaction between different phases and the effect of liquid surface tension on gas-liquid interfaces. Experimental data indicated that the presence of the SDS in the liquid phase augmented the overall gas holdup up to 25% at a constant gas velocity (Ug = 7.3 cm.s−1) in the transition regime, which is due to the role of SDS in bubble interactions. The impact of SDS addition on the mass transfer is twofold. Firstly, it reduced kL because the SDS molecules migrate towards the bubble-liquid interface thanks to the lower O2 diffusivity in water, thus hindering the O2 transfer from one phase to the other. Secondly, it increased aL owing to the inhibition of bubbles coalescence and, therefore, the lower mean bubble size. Among these two effects, the latter is prevailing, which led to an increase in kLaL in contaminated systems. In the second part of this work, a population balance model (PBM) was coupled with a computational fluid dynamics (CFD) model based on large-eddy simulation (LES) to analyze the effect of both tap water and SDS contaminated systems on the breakage phenomena, local flow pattern, and the resulting hydrodynamics and mass transfer features in the reactor. Ultimately, experiments and numerical simulations agreed well in terms of global gas holdup and kLaL coefficient. In particular, the transition points in the case of the SDS media (except for foam formation) provided the model with adequate PBM definitions for the dispersed phase.

Synergy in the Microbial Cyclic Lipopeptide/Petroleum-Derived Surfactant Mixture Can Reduce the Total Surfactant Consumption

We report the synergistic effect of the addition of a microbial cyclic lipopeptide, surfactin (SF), to the most common petroleum-derived surfactant, sodium dodecyl sulfate (SDS). The addition of a small amount of SF (0.1 mol %) to an aqueous solution of SDS reduces the critical micelle concentration (CMC) of SDS from 10–3 to 10–6 M order. The addition of SF to SDS at various ratios lowered the surface tension at the CMC of SDS, indicating CMC reduction and, thus, the minimization of total SDS consumption without loss of surface activity. Surface tension measurement and nuclear magnetic resonance spectroscopy were conducted to analyze the synergy between SDS and SF in aqueous solutions as a function of composition. The interaction parameters of the mixed monolayer and mixed micelles were negative, indicating the occurrence of attractive interactions between SDS and SF, which were stronger than those among the individual surfactants. Moreover, the surface tension at the CMC, area occupied per surfactant molecule, difference in the interaction parameter, and 1H NMR chemical shift values of the SDS/SF mixtures as a function of their composition exhibited an extremum at a mole fraction of 0.7. These results suggest that SF has the peculiarities of encapsulation of the anionic surfactant of SDS within the inner cavity and can screen the electrostatic repulsion of SDS via the formation of their inclusion complex at SDS:SF = 2:1, which facilitates the formation of mixed monolayers and micelles in a more stable state.

Sequentially Selective Coalescence of Binary Self-Propelled Droplets upon Collective Motion

Subsequent synthesis and detection using droplets as microreactors have shown promise in the development of novel materials and drugs because microreactors enable small-scale synthesis and detection of covalent/non-covalent intermolecular interactions. Self-organization exhibited by autonomous droplets under non-equilibrium conditions is beneficial for manipulating the sequentiality and selectivity of droplet coalescence because expensive equipment or elaborate techniques are not required with the autonomy of droplets. However, to our knowledge, selective coalescence caused by the collective motion of self-propelled droplets has not been demonstrated in inanimate systems. Here, we report sequentially selective coalescence based on the dynamic collective pattern of self-propelled droplets composed of ethyl salicylate (ES) or butyl salicylate (BS). When ES and BS droplets were placed on an aqueous sodium dodecyl sulfate (SDS) solution, the collective motion of droplets resulted in three stages of selective coalescence on the time development. Initially, coalescence was observed only between different types of self-propelled droplets. Subsequently, the formed droplets selectively coalesced with ES droplets. Finally, mature droplets merged with BS droplets. The sequentially selective coalescence was discussed from the dynamic pattern formation of swarming droplets and the collapse of the SDS monolayer at the o/w interface caused by the difference in Laplace pressure and the interfacial instability at the contact point between droplets. Thus, this study formulates a strategy of sequentially selective coalescence of droplets via the collective motion of non-identical self-propelled droplets, promoting a new type of powerful and efficient automation technology based on an autonomous inanimate manner of spatiotemporal pattern formation under non-equilibrium conditions for the droplet manipulation.

Online Microfluidic Production of Sustainable Cyrene™-Derived Porous Microparticles

The use of sustainable raw materials is now a necessity in all industries, including the production of porous microparticles. Cyrene™ is a cellulose-derived compound that is readily prepared through the reduction of the α,β-unsaturation of levoglucosenone (LGO)—a wood-based platform molecule. In this work, the importance of Cyrene™ as a potential bio-based molecule to produce sustainable porous microparticles is demonstrated. First, a methacrylic derivative of Cyrene™ (m-Cyrene) was synthesized. A microfluidic co-flow device was then established to produce m-Cyrene-based oil-in-water (O/W) controlled-size emulsions and to polymerize them by ultraviolet (UV) radiation in a vial. The continuous phase was a sodium dodecyl sulfate aqueous solution, and the dispersed phase was a mixture of m-Cyrene with methacrylic anhydride (MAN) at two different mass concentrations (i.e., 1 wt.% MAN and 92 wt.% MAN) and 2,2-dimethoxy-2-phenylacetophenone (DMPA) as a photoinitiator. The process used the lowest possible quantity of raw materials and avoided excessive purifications to produce homogeneous porous m-Cyrene-MAN microparticles. The controlled size and homogeneous size distribution of the produced polymer microparticles were confirmed by scanning electron microscope (SEM) images. The 3D microstructure as well as the porosity were determined using X-ray microtomography. The high-resolution 3D images produced indicate that the pores of the microparticles are homogeneous and that their porosity is controllable through the concentration of MAN in the monomer mixture (porosity of 30% for a 1 wt.% MAN ratio and 2% for a 92 wt.% MAN ratio). Such porosity control is very important for future potential encapsulation processes that require precise release control.

Microflow of nanoemulsion threads in surfactant solutions.

We experimentally investigate the microfluidic flow of oil-in-water nanoemulsions in aqueous sodium dodecyl sulfate (SDS) solutions having different concentrations and injection flow rates. A coaxial microfluidic device is employed to explore the behavior of nanoemulsion threads in these sheathing SDS solutions. Using two high-speed cameras, which simultaneously capture both top and side views, we reveal a variety of flow phenomena, ranging from simple core-annular flow to complex flows, such as gravitational, inertial, and buckling thread flows. By analyzing these complex flows, we develop a methodology that elucidates the relationship of core-annular and gravitational flows at low flow rates. Further, we examine the off-axis displacements and bending of core threads at large flow rates, and we study the buckling dynamics of nanoemulsion threads subjected to osmotic stresses caused by large SDS concentrations in the sheathing fluid.

Study on the effect of graphene/Fe3O4 film on friction and wear performance under water lubrication

In this paper, the corrosion film of Sodium Dodecyl Sulfate (SDS) and graphene aqueous solution has been studied. The results showed that the corrosion film is a kind of graphene/Fe 3 O 4 film, representing the positive effect of tribological performance under water lubrication. Under the protection of graphene/Fe 3 O 4 film, the friction coefficient of steel decreases from 0.41 to 0.17, and the wear scar depth falls from 2.57 μ m to 0.98 μ m at load of 2 N . Graphene/Fe 3 O 4 film exhibits excellent tribological properties under water lubrication due to three reasons. Graphene and Fe 3 O 4 are both antifriction materials, effectively reducing the friction coefficient and wear rate under water lubrication. The hydrophilicity of graphene/Fe 3 O 4 film is significantly improved, making graphene enter the gap between friction pairs easily. As a result, the pitting in the corroded surface can continuously collect and release the Fe 3 O 4 and graphene. These antifriction materials can work longer. Under the synergistic effect of the above three aspects, graphene/Fe 3 O 4 film had excellent friction reducing and anti-wear effect under water lubrication. • Graphene/Fe 3 O 4 film can be prepared on the AISI-52100 steel surface as Fe 3 O 4 can adsorb graphene. • Graphene/Fe 3 O 4 film improves the tribological properties of AISI-52100, reducing the friction coefficient by 59 % and the wear scar depth by 61 %. • The graphene/Fe 3 O 4 film can play a role in reducing friction and wear mainly due to the following three points: antifriction of graphene and Fe 3 O 4 , the increase of wettability of the graphene/Fe 3 O 4 film, the collection and release mechanism of graphene and Fe 3 O 4.

Experimental investigation of hydrate formation kinetics and microscopic properties by a synthesized ternary gas mixture with combination additives

Given the recycling, environmental friendliness and other advantages, hydrate-based gas separation (HBGS) technology has recently gained considerable attention. This work examined synthesized ternary gas mixture (CH4/CO2/N2) hydrate formation kinetics with both cyclopentane (CP) and sodium dodecyl sulfate (SDS) as additives under 7.0 MPa at different temperatures (275.1, 280.1, 295.1 and 290.1 K). Two volume ratios of CP and SDS aqueous solution were used. Hydrate samples were analyzed by powder X-ray diffraction (PXRD), Raman spectroscopy, and cryo-scanning electron microscopy (Cryo-SEM) to reveal the microscopic influence mechanism of additives on hydrates. It was found that the use of mixed additives clearly promotes the hydrate formation kinetics, while enhancing gas separation under some special conditions. Ternary mixed gas with CP and SDS can form a hydrate, in which structure I and II coexisted. CO2 molecules can be encaged in both small and large cages in hydrate. However, CH4 molecules occupied only the small cage of structure I hydrate except with 0.01% SDS with volume ratio of CP and solution at 0.308 and 0.03% SDS with the volume ratio of CP and solution at 0.154. The increasing SDS concentration can smoothen the hydrate crystal surface, thereby inducing more complete crystallization.

Use of green-modified micellar liquid chromatography for the determination of Imidocarb dipropionate residues in food samples

Imidocarb dipropionate (IMD) is broadly utilized in veterinary medicine as an antimicrobial to cure many illnesses, particularly anaplasmosis in livestock. Consequently, the rapid determination of IMD residues in edible bovine food samples is of high significance to guarantee food safety. In the meantime, the environmental influences must be considered to reduce the hazardous impacts of control laboratories. Modifying micellar liquid chromatography (MLC) using a natural deep eutectic solvent (NADES), generated utilizing choline chloride (ChCl) and ethylene glycol (EG), was successfully applied to determine imidocarb (IMD) residues in bovine food samples including meat, liver, kidney, and milk. An experimental design approach was employed for multivariate optimization of important mobile phase factors comprising the concentration of sodium dodecyl sulfate (SDS) in mole L-1, and the percentage volumes of NADES, and ethanol (EtOH). The optimal sustainable mobile phase composition was conquered through the Box Behnken design (BBD) optimization approach considering chromatographic peak height, and peak width at 50% of its height (W 50%) as influential responses. The optimal composition of the modified micellar mobile phase was found to be 0.075 M aqueous SDS solution with Ethanol and NADES in the ratio (40:50:10) with pH adjusted to 4.0 using 0.2 M acetic acid solution. At this optimal composition, IMD was efficiently eluted within 0.8 min when the flow rate was 1 mL/min with no interference by endogenous components and proteins in bovine food samples. Pretreatment of food samples was performed by extracting with an aqueous solution of SDS surfactant only. No organic solvent was required during the extraction step. To validate the presented methodology, the regulations of the Food and Drug Administration (FDA) for bioanalytical analysis were applied. The greenness of the proposed method was estimated utilizing three measures involving the Complementary Green Analytical Procedure Index (ComplexGAPI), the Analytical GREEnness metric (AGREE), and the modern White Analytical Chemistry (WAC) assessment tool. Using these tools, a comparative study was conducted between the proposed method and previously reported liquid chromatographic methods. The proposed method was found to be the most sustainable.

Exploring the effects of selected essential amino acids on the self-association of sodium dodecyl sulphate at different temperatures

Sodium dodecyl sulphate (SDS) has well established biological applications in the determination of molecular weights and structure determination of proteins, peptides etc. Due to these reasons, the study of SDS interactions with essential amino acids (AAs) can be valuable as they can diversify the use of SDS in applications of importance in biology and drug delivery designs etc. The aggregation process of SDS and its detailed physiochemical properties in aqueous system, in the presence and absence of three essential amino acids L-Threonine (THR), DL- Methionine (MET) and L-Phenylalanine (PHE), is studied in a temperature range of 293 K-323 K using conductivities, surface tension (γ), particle size and zetapotential measurements using dynamic light scattering (DLS) technique. From conductivity measurements, critical micelle concentration (CMC), counterion binding (β) and thermodynamic parameters such as standard free energy change of micellization (ΔGmo), standard enthalpy change of micellization (ΔHmo), standard entropy change of micellization (ΔSmo) etc., are calculated. The surface properties and interfacial parameters of SDS systems are studied using surface tensiometery. Results established that the presence of amino acids (AAs) reduced the CMC of SDS. The electrostatic interaction of AAs with charged micellar surface were also observed. The micellization process of SDS was found thermodynamically feasible in the aqueous amino acid (AAA) system. From the surface tension data, interfacial parameters such as Гmax, Amin,pC20 , and surface effectiveness of SDS in aqueous and AAA system have been calculated and compared. It was revealed that surface adsorption and rearrangement of SDS molecular ion at their micellar concentration at air/liquid interface are significantly affected by AA addition. Hydrodynamic diameter (Dh) and zetapotential (ζ) of aqueous SDS solution helped to check the effect of amino acid additives on the colloidal size and stability of SDS aggregates. The results from different techniques were consistent to establish the feasibility of SDS micellization process in aqueous as well as aqueous AA solution.

Heat reversal phenomenon of spray cooling and its heat transfer enhancement characteristics

Aiming at the requirements of the heat dissipation for high heat flux laser medium, an experimental platform was designed and built. The spray cooling of heat transfer enhancement experiment with different concentrations of sodium dodecyl sulfate aqueous solution as the working fluid was studied. The results show that within a specific range of heat flux density, as the heat flux density increases, the temperature of the heating surface does not rise but drops, which was named heat reversal. The heat reversal phenomenon increased the convective heat transfer coefficient by as much as 94.0%. The heat flux density range corresponding to heat reversal was 80−130 W/cm2, which had a weak relationship with concentration. This means that, in spray cooling, an increment in heat load can cause a temperature drop of the heated surface under certain circumstances. This phenomenon only occured when the heat flux density was gradually increasing, and it was not found in the process of reducing and adjusting the heat flux density. Surfactant boiling in the pool will also cause thermal reversal, but the specific reason remains to be studied.

Active Control of Boundary Lubrication of Ceramic Tribo-Pairs in Sodium Dodecyl Sulfate Aqueous Solutions

The objective of the study is to actively control friction between engineering ceramics in underwater applications. By designing a proper electrode system and applying an external electric field, the active control of friction between Al2O3 plate and ZrO2 ball in sodium dodecyl sulfate (SDS) aqueous solutions has been realized, which is different from the previous studies of potential-controlled boundary lubrication where at least one part of tribo-pairs is a conductor. Reversible change of friction coefficient has been observed in the range from 0.12 to 0.35. An indirect electric field-assisted adsorption/desorption model has been proposed to explain the observed phenomena. The addition of inorganic salts containing counterions to the SDS solution or increasing the concentration of SDS can shorten the response time of friction to the variation of the applied electric field by facilitating the formation of SDS micelles. This opens a new way to realize the active control of friction for insulative tribo-pairs without corrosion.

Effects of catanionic surfactant mixture adsorption on the wettability of PTFE and PMMA

Surfactants can regulate the wettability of a liquid on a solid substrate as they adsorb to solid-liquid and gas-liquid interfaces. In the present work, a catanionic surfactant mixture, sodium dodecyl sulfate (SDS) and dodecyltrimethylammonium bromide (C12TAB) mixed at a molar ratio of 2:1, showed outstanding synergistic effect in improving the wettability of low energy substrates (PTFE and PMMA). The adsorption behaviors of the catanionic surfactant mixture on PTFE and PMMA substrates were studied. The surface tensions and contact angles of aqueous solutions of SDS, C12TAB, and their mixture on PTFE and PMMA were measured, and the adhesion tension and adhesion work were calculated. Compared to individual SDS and C12TAB, the SDS-C12TAB mixture formed a compactly arranged layer at the PTFE-aqueous interface, thereby leading to a more significant hydrophilic modification of PTFE. In the PMMA system, the SDS-C12TAB mixture adsorbed to the PMMA-aqueous interface through acid-base interactions between the positively charged surfactant headgroups and the basic groups at PMMA surface and increased the hydrophobicity of the PMMA substrate at low surfactant concentrations. When the surfactant concentration exceeded the critical micelle concentration (CMC), the surfactant started to adsorb to the PMMA-aqueous interface through hydrophobic interactions between the hydrophobic surfactant tails and the nonpolar sites at PMMA surface, which further improved the wettability of PMMA. Overall, the wettability of low energy substrates can be significantly improved under the strong synergistic effect of commercial anionic and cationic surfactants without need of complex synthesis of new amphiphiles. Therefore, the catanionic surfactant mixtures may be a very promising system for regulating wettability.