Cloud Point Phenomenon Research Articles

Spectrophotometric and DFT study of Germanium(IV) interaction with 6,7-dihydroxy-2,4-diphenyl-1-benzopyran-1-ium bromide in solutions: Room-temperature cloud point extraction and its analytical application

In the current study, a novel and fast procedure for room-temperature cloud point extraction of Germanium (VI) followed by spectrophotometric detection is developed. A 6,7-dihydroxy-2,4-diphenyl-1-benzopyran-1-ium bromide (DPBP) reagent was proposed for binding Ge (IV) into the extractable colored complex. The interaction of Ge (IV) with the reagent DPBP was studied using spectrophotometry and density functional theory (DFT) calculations. It was established that the complex stoichiometry is 1:2. It was shown that with the increase of the charge of the resulting complex, the Gibbs free energy of the complex formation increases considerably. This means that the formation of neutral species with cis- location of the hydroxyl ligands is the most preferable process. The cloud point phenomenon at room temperature was immediately initiated via ammonium benzoate. The calibration plot for Ge (IV) was obtained in the concentration range of 4–490 μg L−1 under optimized conditions: pH = 1, concentration of DPBP 1.8–2∙10-5 mol/L, 0.12 mol/L aqueous ammonium benzoate and 1 % (v/v) Triton X-100). The limit of detection is 1.2 μg L−1. The method was successfully applied to the determination of Ge(IV) traces in vegetable and rock samples.

Physicochemical insights into cloud point phenomenon of Triton X-100 on carbon nanofibers

Triton X-100 exhibits wide application potential as emulsifier, foaming and dispersion agent which are hampered by its temperature-sensitive behavior. It is a manifestation of the cloud point (CP) phenomenon of Triton X-100. Carbon nanomaterials are frequently dispersed with Triton X-100; however, the temperature-driven self-assembly behavior of the surfactant has never been discussed on such nanomaterials. The shape of Triton X-100 micellar aggregates in an aqueous medium or at the surfaces in itself is not clear and needs further explorations. The present study is performed to address both of these facets of Triton X-100. It discusses the CP phenomenon of Triton X-100 on carbon nanofibers (CNF) in an aqueous medium and at the surface of dispersed and acid-modified CNF at high temperature. For the very first time, the spherical-shaped micelles of Triton X-100 are visualized on CNF in an aqueous medium via FESEM and HRTEM studies. At the surface of CNF, the hemispherical-shaped micellar aggregates are formed. This unique behavior is attributed to the surface area and special morphological features of CNF, geometry, concentration and temperature-sensitive behavior of Triton X-100. It is hoped that this study will lead to better understanding of the interfacial mechanisms between Triton X-100 and carbon nanomaterials. The modified CNF exhibited good mechanical strength also so they are expected to foster thriving research fields such as flexible electronics.

Influence of electrolytes on the cloud point phenomenon of tween-80+lomefloxacin hydrochloride mixtures and their thermodynamic parameters

Herein, the interaction between Tween-80 (Tw-80) and antibiotic drug lomefloxacin hydrochloride (LMFH) has been studied through the cloud point (CP) measurement of Tw-80 + LMFH mixtures in the absence/attendance of electrolytes. Tw-80 is used for different formulations of drugs and foods. LMFH is widely prescribed for the treatment of numerous bacterial infections. The cloud point (CP) values of Tw-80 + LMFH mixture were determined and found to reduce with the augmentation of concentration of LMFH. The occurrence of salts reduces the CP of the Tw-80 + LMFH mixture which further enhances with an increase of salt concentration. The effectiveness of electrolytes in decreasing CP of Tw-80 + LMFH mixture was obtained to be followed the order: CPNaCl < CPNa2SO4 < CPNa3PO4. 12 H2O which reveal that Na3PO4. 12 H2O is the most effective CP suppressor. The Gibbs free energy (∆Gco) value was achieved positive in entire systems and the positive ∆Gco value was lowered in the salt medium. The ∆Gco values were also dwindled through the augmentation of LMFH/electrolytes content in the solution. The enthalpy (∆Hco) and entropy (∆Sco) value of this system was found to be negative which drops with the rise of LMFH/electrolytes content. In addition, different thermodynamic properties of transfer along with entropy-enthalpy compensation was computed to clarify the interaction between Tw-80 and LMFH.

Novel insights into the dispersed and acid-mediated surface modification of the carbon nanofibers

Carbon nanofibers (CNF) are the state of art materials owing to their special morphological features. In the pristine form, they exhibit strong van der Waals interactions which keep them agglomerated. The actual potential of these nanofibers could be realized once these are unbundled. In this work, CNF have been dispersed with Triton X-100 during ultrasonication, and further functionalized using 3:1 mixture of H2SO4 and HNO3 via reflux method. The effects of different concentrations of Triton X-100 (1–3 ml) on the dispersion and functionalization of CNF have been studied. CNF have been functionalized with O, N and S functionalities. The results have been elicited using FESEM, EDS, FTIR and RAMAN techniques. Triton X-100 wrapping covers up many (if not all) of the reactive edge sites on CNF. Additionally, the Cloud point phenomenon has been observed owing to the temperature behavior of adsorbed Triton X-100 layers on to CNF. Direct functionalization of CNF has been observed to be destructive towards their morphology. Acid functionalized CNF are intended for the electrochemical, nanocomposites, ink-jet printing, sensing applications etc.

Understanding and Prediction of the Clouding Phenomenon by Spontaneous and Effective Packing Concepts

AbstractIn this work, we show by which mechanism branching of the hydrocarbon chains influences the cloud point of nonionic, ethoxylated surfactants. The temperature‐induced separation into a dilute and a concentrated liquid phase is of liquid–gas type and can be explained by the relative probability of endcaps and branching points of the cylindrical micelles in both phases. The influence of branches on the hydrocarbon chains can be easily understood by means of spontaneous and effective packing concepts, while quantification via hydrophilic/lipophilic balance (HLB), hydrophilic‐lipophilic difference (HLD), and HLD‐Net Average Curvature requires parametrization. The phase equilibrium above the cloud point phenomenon is equivalent to the Winsor I type phase equilibrium, one of the five known phase equilibria in ternary systems.

An integrated strategy for extraction and pre-concentration of four astragalosides from Radix Astragali by a formulated surfactant aqueous system

Integrated and environmentally friendly methods for extraction and enrichment of natural products have gained increasing interests. The proposed preparation process provides the possibility that extraction and pre-concentration for astragalosides from Radix Astragali roots can be conducted with the surfactant aqueous system in one single procedure. The formulated surfactant system composing of 2% TX-114 as surfactant and 0.03% (w/v) of Gemini 16-5-16 as co-surfactant showed higher extraction efficiency with ultrasonic-assisted method and four astragalosides could be enriched by the cloud point phenomenon of surfactant. This work represents a valuable alternative for the eco-friendly extraction and enrichment of secondary metabolites from plants.

The cloud point phenomenon of ionic surfactants: A view from molecular dynamics and metadynamics simulation

Molecular dynamics (MD) and metadynamics simulations were used to give an understanding on the cloud point phenomenon of ionic surfactants. Meanwhile, the differences between tetrabutylammonium interactions with dodecyl sulfate (DS−) and alkyl carboxylate (C12) micelles are discussed. Micelle ionization degree (α), binding patterns between the counterions and micelle, potential of mean force (PMF), and intermicellar interactions were characterized to present a reasonable explanation on the different behaviors of tetrabutylammonium alkyl carboxylate (TBAC) and tetrabutylammonium dodecyl sulfate (TBADS). Free energy profiles indicate that three bridging models exist between TBADS micelles. This will be the fundamental intermicellar model to interpret the cloud point phenomenon of TBADS ionic surfactants and other analogous systems.

Salicylic acid assisted cloud point extraction at room temperature: Application for preconcentration and spectrophotometric determination of molybdenum(VI)

In this study, a novel and rapid procedure for the salicylic acid assisted cloud point extraction of molybdenum(VI) is presented. Preconcentration of the substrate has been suggested prior to its spectrophotometric determination method. The method involves the complexation of Mo(VI) with 6,7-dihydroxy-4-methyl-2-phenylbenzoryrylium chloride (DHMPhB), followed by extraction of the complex into micellar phase of Triton X-100. The cloud point phenomenon at room temperature was activated by formation of salicylic acid. This reaction prevents the formation of hydrogen bonds between surfactant and water molecules and causes immediate formation (<1 min) of the surfactant-rich phase. The calibration curve for Mo(VI) was obtained in the concentration range of 0.16–1.8 μg mL−1 under optimized conditions (pH 2; 1·10−4 M DHMPhB; 0.1 M NaSal; 0.05 M H2SO4 and 1% (v/v) Triton X-100). The limit of detection is 0.05 μg mL−1. The method was successfully used to determine trace quantities of Mo(VI) in water samples, the rose hips and pharmaceuticals with favorable results.

Surface Adsorption and Micelle Formation of Polyoxyethylene-type Nonionic Surfactants in Mixtures of Water and Hydrophilic Imidazolium-type Ionic Liquid.

The interfacial properties of polyoxyethylene alkyl ether-type nonionic surfactants (CnEm) were studied in a hydrophilic room-temperature ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (bmimBF4), in the presence of water. These properties were assessed using static surface tension, pyrene fluorescence, and dynamic light scattering measurements. The interfacial properties were strongly dependent on the solution composition. Increased water concentration lowered the critical micelle concentration (cmc). The cmc was also affected by the lengths of both the alkyl and polyoxyethylene chains, but a greater impact was observed for the alkyl chain length. These results indicate that micellization occurs as a result of solvophobic interaction between surfactant molecules in the water/bmimBF4 mixed solutions, similar to aqueous surfactant systems. The cloud point phenomenon was observed for CnEm with a relatively low hydrophilic-lipophilic balance (HLB) value, and the relationship between the cloud point and water/bmimBF4 composition exhibited a convex upward curve. Furthermore, the mixing of bmimBF4 with water increased the surfactant solubility for water-rich compositions, suggesting that bmimBF4 acts as a chaotropic salt.

Cloud Point Phenomena in the (Aniline or N,N-Dimethylaniline + Water) Solutions, and Cosolvent Effects of Liquid Poly(ethylene glycol) Addition: Experimental Measurements and Modeling

In this work, liquid phase behavior (cloud point phenomena) was studied for two binary and four aqueous pseudobinary systems containing aniline or N,N-dimethylaniline and poly(ethylene glycol) 200 or poly(ethylene glycol) 400, (PEG200 and PEG400, respectively) in the temperature range T = (290.15 to 351.15) K and an ambient pressure of 0.1 MPa. Experimental data (cloud-points) were obtained by the visual cloud point method. The studied systems exhibit an upper critical solution temperature (UCST) type of phase behavior and the immiscibility increases with increasing the average molar mass of poly(ethylene glycols). PEG200/PEG400 showed as a good cosolvent for aniline in water. The experimental data were correlated using non-random two-liquid model (NRTL) with one form of temperature dependent parameters.

Simple and useful method for determination of inorganic selenium species in real samples based on UV-VIS spectroscopy in a micellar medium

A preconcentration and determination methodology utilizing the cloud point phenomenon was developed for the determination of inorganic selenium species using UV-VIS spectrophotometry.

Cloud point extraction of platinum group elements and gold: elimination of nitric acid-related problems with sulphamic acid

Microwave-assisted cloud point extraction (CPE) of platinum group elements (PGEs) and Au in solutions containing aqua regia using 2-mercaptobenzothiazole (2-MBT) was studied. For comparison, the extractions were also performed in hydrochloric acid and nitric acid solutions. A previously published CPE method, employing 2-MBT in hydrochloric acid solutions, was used as a reference method in order to investigate the effect of added nitric acid on the recoveries of Ru, Rh, Pd, Ir, Pt and Au. The results indicated that the presence of nitric acid did not cause problems to the cloud point phenomenon, but had an effect on the complexation processes of 2-MBT, thus leading to low recoveries. Therefore, a novel approach of adding sulphamic acid to enhance the extraction efficiencies of the PGEs and Au in the CPE performed in solutions containing aqua regia was investigated. A clear increase in the recoveries of PGEs and Au in solutions containing aqua regia or nitric acid was observed when sulphamic acid was used. The recoveries for Ru, Rh, Pd, Pt and Au obtained in optimized conditions were between 80 and 100%. However, the recoveries of Ir remained below 40%. The accuracy of the developed method was evaluated by analysing a certified reference material NIST SRM 2557 (used automotive catalyst).

Oleylethoxycarboxylate – An efficient surfactant for copper extraction and surfactant recycling via micellar enhanced ultrafiltration

The nonaoxyethylene oleylether carboxylic acid Akypo RO90 VG, a surfactant with ionic character at high pH and non-ionic character at low pH, has been investigated with respect to copper removal from aqueous streams via micellar enhanced ultrafiltration (MEUF) with subsequent copper and RO90 separation using the method of cloud point extraction (CPE). Almost quantitative Cu2+ removal is obtained in MEUF and more than 90% Cu2+ is separated from RO90 in CPE. The investigation of Cu2+/RO90 complexes with small-angle neutron scattering (SANS) shows almost no structural change of RO90 micelles in the presence of Cu2+. These results show the importance of the surfactant head group for optimizing the specific interaction with the ion to be extracted. This optimization and the ability to recycle the surfactant by a temperature variation and using the cloud point phenomenon is an elegant approach to achieve efficient metal ion extraction.

Salt Effect on the Cloud Point Phenomenon of Amphiphilic Drug-Hydroxypropylmethyl Cellulose System

Effect of two amphiphilic drugs (tricyclic antidepressant, nortriptyline hydrochloride (NORT), and nonsteroidal anti-inflammatory drug, sodium salt of ibuprofen (IBF)) on the cloud point of biopolymer hydroxypropylmethyl cellulose (HPMC) was studied. Effect of NaCl was also seen on the CP of HPMC-drug system. CP of HPMC increases uniformly on increasing the (drug). Both drugs, though one being anionic (IBF) and other cationic (NORT), affect the CP in almost the same manner but with different extent implying the role of hydrophobicity in the interaction between drug and polymer. Salt affects the CP of the drug in a dramatic way as low concentration of salt was only able to increase the value of the CP, though not affecting the pattern. However, in presence of high concentration of salts, minimum was observed on CP versus (drug) plots. Various thermodynamic parameters were evaluated and discussed on the basis of the observed results.

Salinity Effect in Cloud Point Phenomena by Nonionic Surfactants Used in Enhanced Oil Recovery Tests

The cloud point phenomenon for solutions of polyoxyethylene (POE)-type nonionic surfactants (B, C, D, and E) in different salt concentrations was investigated. The cloud point temperature, T c , increased with elongation of the POE chain. This demonstrated that the solvophilicity of the surfactants comes from POE chain. Thus, the cloud point decreased with increase of salt concentration. Surfactants D and E were the only ones that showed cloud point temperatures above the average temperature of oil wells (~70°C), even at high concentrations of salt, and surfactant E was most suitable for enhanced oil recovery operations.

Toward a Quantitative Model and Prediction of the Cloud Point of Normal Nonionic Surfactants and Novel Gemini Surfactants with Heuristic Method and Gaussian Process

A systematic study of integrating statistical modeling and experimental analysis to investigate the cloud point (CP) and environmental risk of 82 structurally diverse nonionic surfactants is performed. During this procedure, the structural profiles of the studied compounds are characterized using hydrophilic domain and the whole molecular. Hundreds of descriptors, including constitutional, topological, geometrical, and electrostatic were calculated by the CODESSA program, and the resulting variables of the characterization selected by heuristic method are then modeled by the Gaussian process (GP). A variety of regression techniques, including MLR, PLS, SVM, and LSSVM are performed to a comprehensive comparison with GP on the basis of statistical analysis and experimental properties, in conjunction with the sophisticated variable selection methods, that is, empirical heuristic strategy. Among all the built models, the most predictable one is constructed based on the GP modeling combination of heuristic variable selection related to hydrophilic domain, with its predictive coefficient of determination () and root-mean-square error of prediction (RMSP) on external independent test set of 0.962 and 5.200, respectively. The statistic model shows that the CP phenomenon is a comprehensive interaction of relative molecular weight, moments of inertia A, and topological structure account for hydrophilic part.

An aqueous anionic/nonionic surfactant two-phase system in the presence of salt. 1. Rheological behavior and microstructure

Aqueous binary surfactant solutions, based on the cloud point phenomenon, have been utilized to design efficient extraction of a variety of substances. In this study, the effect of the anionic surfactant sodium dodecyl sulfate (SDS) on the clouding behaviour of aqueous nonionic surfactant solutions of Triton X-114 (TX-114), in the presence of 100 mM sodium chloride (NaCl), has been studied as a function of temperature by means of turbidity, dynamic light scattering (DLS), and rheo-small angle light scattering (Rheo-SALS). It is found that the addition of 2 mM SDS lowers the phase separation temperature of the surfactant solution by about 2 °C. The hydrodynamic radius of the surfactant aggregates increases with increase of temperature and SDS concentration. The change in microstructure of the surfactant aggregates at different temperature and SDS concentrations is also reflected by the characteristic length and aspect ratio extracted from their SALS patterns, which range from 269 to 623 nm and from 1.01 to 1.40, respectively. The increasing characteristic length and aspect ratio with SDS concentration indicate the growth of the mixed surfactant aggregates is in the flow direction and these elongated aggregates can align under shear.

Surfactant Systems for EOR in High-Temperature, High-Salinity Environments

Summary A systematic study was made of phase behavior of alkoxyglycidylether sulfonates (AGESs). These surfactants were screened with either NaCl-only brines or NaCl-only brines and n-octane at water/ oil ratio (WOR) ~1 for temperatures between approximately 85 and 120°C. All test cases were free of alcohols and other cosolvents. Classical Winsor phase behavior was observed in most scans, with optimal salinities ranging from less than 1% NaCl to more than 20% NaCl for AGESs with suitable combinations of hydrophobe and alkoxy chain type [ethylene oxide (EO) or propylene oxide (PO)] and chain length. Oil solubilization was high, indicating that ultralow interfacial tensions existed near optimal conditions. The test results for 120°C at WOR~1 have been summarized in a map, which might provide a useful guide for initial selection of such surfactants for EOR processes. Saline solutions of AGESs separate at elevated temperatures into two liquid phases (the cloud-point phenomenon), which may be problematic when they are injected into high-temperature reservoirs. An example is provided that indicates that this situation can be alleviated by blending suitable AGES and internal olefin sulfonate (IOS) surfactants. Synergy between the two types of surfactant resulted in transparent, single-phase aqueous solutions for some blends, but not for the individual surfactants, over a range of conditions including in synthetic seawater. Such blends are promising because both AGES and IOS surfactants have structural features that can be adjusted during manufacture to give a range of properties to suit reservoir conditions (temperature, salinity, and crude-oil type).

Determination of Vanadium in Food Samples by Cloud Point Extraction and Graphite Furnace Atomic Absorption Spectroscopy

A preconcentration methodology utilizing the cloud point phenomenon is described for the determination of total vanadium by graphite furnace atomic absorption spectrometry. Cloud point extraction method was based on the formation of a ternary complex between vanadium, 2-(2´-thiazolylazo)-p-cresol, and ascorbic acid, with subsequent extraction–preconcentration of the formed complexes using Triton X-100. Optimization of different parameters was evaluated. Under optimal conditions, a calibration curve was constructed, showing a linear range of 1.0–60 ng mL−1 and the limit of detection and relative standard deviation for preconcentration of a 10-mL sample were found to be 0.05 ng mL−1 and 3.9%, respectively. The preconcentration factor was found to be tenfold for 10 mL of water sample. The technique has been applied succesfully to the determination of vanadium traces in wine, tea, and tomato samples and the recoveries of added vanadium were in the range 96–102%.

Selective Determination of Copper in Water Samples by Atomic Absorption Spectrometry after Cloud Point Extraction

A preconcentration methodology utilizing the cloud point phenomenon is described for the determination of copper by flame atomic absorption spectrometry. The reagent Sulfathiazolylazo resorsin was used as a complexing agent. The preconcentration factor of 25-fold was obtained. The calibration curve is linear in the range of 4–400 µ g L−1 with a limit of detection of 0.64 µ g L−1. The relative standard deviation (n = 5, 12 µ g L−1) was 3.5%. The cloud point is formed in the presence of phenol at room temperature. The method was successfully applied to the determination of copper in water samples and a standard reference material.