Clouding, surfactants

Many solutions of common nonionic surfactants and water separate into two phases when heated above a certain temperature (the cloud point), and some investigators call the phase of greater surfactant concentration, a microemulsion. Thus, there is not even universal agreement that a microemulsion must contain oil. 

Poly(methyl vinyl ether) [34465-52-6] because of its water solubility, continues to generate commercial interest. It is soluble in all proportions and exhibits a well-defined cloud point of 33°C. Like other polybases, ie, polymers capable of accepting acidic protons, such as poly(ethylene oxide) and poly(vinyl pyrroHdone), each monomer unit can accept a proton in the presence of large anions, such as anionic surfactants, Hl, or polyacids, to form a wide variety of complexes. 

A stable cloud of water ia fuel usually means that a surfactant is present to form a stable water-ia-oil emulsion. Smaller droplets resist natural coalescence processes. A surfactant that is potent as an emulsifying agent is apt to disarm the coalescing filters, aHowiag excess water to be deUvered with fuel. 

In most cases, these active defoaming components are insoluble in the defoamer formulation as weU as in the foaming media, but there are cases which function by the inverted cloud-point mechanism (3). These products are soluble at low temperature and precipitate when the temperature is raised. When precipitated, these defoamer—surfactants function as defoamers when dissolved, they may act as foam stabilizers. Examples of this type are the block polymers of poly(ethylene oxide) and poly(propylene oxide) and other low HLB (hydrophilic—lipophilic balance) nonionic surfactants. 

Two kinds of barriers are important for two-phase emulsions the electric double layer and steric repulsion from adsorbed polymers. An ionic surfactant adsorbed at the interface of an oil droplet in water orients the polar group toward the water. The counterions of the surfactant form a diffuse cloud reaching out into the continuous phase, the electric double layer. When the counterions start overlapping at the approach of two droplets, a repulsion force is experienced. The repulsion from the electric double layer is famous because it played a decisive role in the theory for colloidal stabiUty that is called DLVO, after its originators Derjaguin, Landau, Vervey, and Overbeek (14,15). The theory provided substantial progress in the understanding of colloidal stabihty, and its treatment dominated the colloid science Hterature for several decades. 

Recent publications indicate the cloud-point extraction by phases of nonionic surfactant as an effective procedure for preconcentrating and separation of metal ions, organic pollutants and biologically active compounds. The effectiveness of the cloud-point extraction is due to its high selectivity and the possibility to obtain high coefficients of absolute preconcentrating while analyzing small volumes of the sample. Besides, the cloud-point extraction with non-ionic surfactants insures the low-cost, simple and accurate analytic procedures. 

In this study we examined the influence of concentration conditions, acidity of solutions, and electrolytes inclusions on the liophilic properties of the surfactant-rich phases of polyethoxylated alkylphenols OP-7 and OP-10 at the cloud point temperature. The liophilic properties of micellar phases formed under different conditions were determined by the estimation of effective hydration values and solvatation free energy of methylene and carboxyl groups at cloud-point extraction of aliphatic acids. It was demonstrated that micellar phases formed from the low concentrated aqueous solutions of the surfactant have more hydrophobic properties than the phases resulting from highly concentrated solutions. The influence of media acidity on the liophilic properties of the surfactant phases was also exposed. 

Based on the calculation of the solvatation free energy of methylene fragment with carboxyl at the aliphatic carboxylic acids extraction, the uniqueness of cloud-point phases was demonstrated, manifested in their ability to energetically profitably extract both hydrophilic and hydrophobic molecules of substrates. The conclusion is made about the universality of this phenomenon and its applicability to other kinds of organized media on the surfactant base. 

For fluorescence PAH determination in tap water acid-induced cloud point extraction was used. This kind of extraction based on the phase separation into two isotropic liquid phases a concentrated phase containing most of the surfactant (surfactant-rich phase), where the solubilised solutes are exttacted, and an aqueous phase containing a surfactant concenttation closes to the critical micellar concentration. 

METHODOLOGICAL ASPECTS OP CLOUD POINT PRECONCENTRATING OF MICRO-ADMIXTURES BY PHASES OF NON-IONIC SURFACTANTS Doroschuk V.O. 

The study of the mechanism of cloud point micellar extractions by phases of non-ionic surfactant (NS) is an aspect often disregarded in most literature reports and, thus, is of general interest. The effective application of the micellar extraction in the analysis is connected with the principled and the least studied problem about the influence of hydrophobicity, stmcture and substrate charge on the distribution between the water and non-ionic surfactant-rich phase. 

Strkcttire inflkence. The specificity of interphase transfer in the micellar-extraction systems is the independent and cooperative influence of the substrate molecular structure - the first-order molecular connectivity indexes) and hydrophobicity (log P - the distribution coefficient value in the water-octanole system) on its distribution between the water and the surfactant-rich phases. The possibility of substrates distribution and their D-values prediction in the cloud point extraction systems using regressions, which consider the log P and values was shown. Here the specificity of the micellar extraction is determined by the appearance of the host-guest phenomenon at molecular level and the high level of stmctural organization of the micellar phase itself. 

THE CLOUD-POINT EXTRACTION OF ALIPHATIC AMINES INTO THE NON-IONIC SURFACTANT-RICH PHASES... 

ACID-BASED SURFACTANT CLOUD POINT EXTRACTION AND PRECONCENTRATION OF POLYCYCLIC AROMATIC HYDROCARBONS PRIOR TO FLUORESCENCE DETERMINATION... 

The aqueous micellai solutions of some surfactants exhibit the cloud point, or turbidity, phenomenon when the solution is heated or cooled above or below a certain temperature. Then the phase sepai ation into two isotropic liquid phases occurs a concentrated phase containing most of the surfactant and an aqueous phase containing a surfactant concentration close to the critical micellar concentration. The anionic surfactant solutions show this phenomenon in acid media without any temperature modifications. The aim of the present work is to explore the analytical possibilities of acid-induced cloud point extraction in the extraction and preconcentration of polycyclic ai omatic hydrocai bons (PAHs) from water solutions. The combination of extraction, preconcentration and luminescence detection of PAHs in one step under their trace determination in objects mentioned allows to exclude the use of lai ge volumes of expensive, high-purity and toxic organic solvents and replace the known time and solvent consuming procedures by more simple and convenient methods. 

Sodium dodecylsulphate was selected as an anionic surfactant Factors affecting acid-induced cloud point extraction including surfactant, hydrochloric acid, PAHs, and electrolyte concentration, centrifugation have been examined. Finally, we applied the optimized acid-induced CPE system for combination of the extraction and preconcentration steps with fluorimetric determination of some representatives of PAHs. Suggested means was used for PAHs determination in tap water. 

Cloud Point Measurements Cloud points were recorded by the visual observation of aqueous solutions containing 1% W/V surfactant. The measurement defines the temperature at which the system under test shows a characteristic transitional change from a clear solution to an opalescent or cloudy state. All cloud points were recorded in both ascending and descending temperature cycles to ensure data confidence. The influence of salt and/or oils on the cloud point were systematically evaluated. 

Cloud Points The influence of added NaCl on the observed cloud points of 1% W/V solutions of the four nonionic surfactants under observation are given in Figure 1. Approximately linear correlations were observed as the aqueous NaCl level was increased, with negative coefficients recorded between 0.22 - 0.3 K.g "1dm3. Higher loadings of surfactant were found to increase the cloud point. It was observed also that the inclusion of small quantities of oils to surfactant solutions could either elevate or depress the cloud point. The significance of this fact will be developed later. 

Figure 1. Cloud point variation for different salinities (Aqueous surfactant loadings - 10 g/dnP)...

Surfactant blends of interest will exhibit clouding phenomena in aqueous solutions undergoing a phase transition from a one phase system to a two phase system at a discrete and characteristic temperature, referred to as the Cloud Point (CP). This value indicates the temperature at which sufficient dehydration of the oxyethylene portion of the surfactant molecule has occurred and this results in its "displacement" from solution. The addition of lyotropic salts will depress the CP, presumably due to the promotion of localised ordering of water molecules near the hydrophilic sheath of the surfactant molecule (8). Furthermore, the addition of different oils to surfactant solutions can induce either an elevation or a depression of the recorded CP and can be used to qualitatively predict the PIT (8x9). 

When scouring synthetic fibres that are to be dyed with disperse dyes, nonionic scouring agents are best avoided unless they are formulated to have a high cloud point and are known not to adversely affect the dispersion properties of the dyes. Conversely, when scouring acrylic fibres, anionic surfactants should be avoided [156] because they are liable to interfere with the subsequent application of basic dyes. These fibres are usually scoured with an ethoxylated alcohol, either alone or with a mild alkali such as sodium carbonate or a phosphate. 

Surprisingly, other investigators were unable to confirm the adverse effect of nonionic surfactants of low cloud point in the high-temperature dyeing of polyester, even in the presence of electrolytes [111]. This was probably because of the rather low concentrations used. Adducts containing a C18-C2o hydrophobe and a decaoxyethylene hydrophile, as well... 

Performance Indices Quality Factors Optimum E1LB Critical micelle concentration (CMC) Soil solubilization capacity Krafft point (ionic surfactants only) Cloud point (nonionic surfactants only) Viscosity Calcium binding capacity Surface tension reduction at CMC Dissolution time Material and/or structural attributes... 

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