Cloud point phenomena

The effect of using mixtures of surfactants on micelle formation, monolayer formation, solubilization, adsorption, precipitation, and cloud point phenomena is discussed. Mechanisms of surfactant interaction and some models useful in describing these phenomena are outlined. The use of surfactant mixtures to solve technological problems is also considered. 

The cloud point phenomena as a lower consolute solution temperature is becoming better understood in terms of critical solution theory and the fundamental forces involved for pure nonionic surfactant systems. However, the phenomena may still occur if some ionic surfactant is added to the nonionic surfactant system. A challenge to theoreticians will be to model these mixed ionic/nonionic systems. This will require inclusion of electrostatic considerations in the modeling. 

Marszall (1988) studied the effect of electrolytes on the cloud point of mixed ionic-nonionic surfactant solutions such as SDS and Triton X-100. It was found that the cloud point of the mixed micellar solutions is drastically lowered by a variety of electrolytes at considerably lower concentrations than those affecting the cloud point of nonionic surfactants used alone. The results indicate that the factors affecting the cloud point phenomena of mixed surfactants at very low concentrations of ionic surfactants and electrolytes are primarily electrostatic in nature. The change in the original charge distribution of mixed micelles at a Lxed SDS-Triton X-100 ratio (one molecule per micelle), as indicated by the cloud point measurements as a function of electrolyte concentration, depends mostly on the valency number of the cations (counterions) and to some extent on the kind of the anion (co-ion) and is independent of the type of monovalent cation. 

As can be noted, the correlation between the calculated and actual results, using a very simple curve fitting technique, yields good fits concerning molar volume, which is examined in terms of density, and in cloud point data, examined in terms of tai jerature. For those not familiar with the cloud point phenomena, nonionic surfactants exhibit inverse solubility characteristics per taiperature increases, i.e., as the... 

In an effort to cloud point phenomena polymer-microemulslon mlcroemulslon systems... 

D, Balzer, Cloud point phenomena in the pha.se behavior of alkylpolyglucosides in water. Langmuir. 9 3375-3.382. 1993. 

If the interaction between an anionic surfactant and a cationic surfactant results in a water-soluble complex, how do we know that the complex is really formed If, indeed, the anionic and cationic surfactants are neutralized, then is the resulting complex a nonionic surfactant and to what extent does it behave like nonionic surfactants Ethoxylated nonionic surfactants have the unique property of cloud point phenomena they become cloudy above a given temperature, known as the cloud point temperature. If, indeed, the resulting anionic-cationic complexes are neutralized, would they exhibit cloud point phenomena The answer to these questions is yes imder special conditions and has been demonstrated previously [36]. In the following subsections, results of surface and interfacial tensions and cloud point phenomena, and additional properties of the complexes will be given. 

If, indeed, a complex containing oxyethylene groups is formed, then it should exhibit cloud point phenomena like ethoxylated nonionic surfactants. This is found to be so as shown in Fig. 8. Note the shift with pH. At different pH s, the number of dissociated APEs is different thus, a different amount of TTAB is needed to neutralize it. The decrease in pH of an APE solution when TTAB is added to it is an indication that a complex is formed. The exhibition of cloud point phenomena for mixtures of APE-TTAB is an indication that the resulting complexes have a pseudononionic character. 

Cloud point phenomena is exhibited only by the complexes and not by their surfactant components. Figure 9 shows cloud point temperature versus anionic mole fraction for a system of anionic-cationic solutions where the additional hydrophilic group is carried by... 

It is important to note that complexes, other than those containing oxyethylene moieties can also exhibit cloud point phenomena. Figure 12 shows the phase diagram of the anionic-cationic surfactant system sodium- -lauroyl-iV-methyl-p-alanine-stearyltrimeth-ylammonium chloride [38]. 

Where they are made compatible under either of the above conditions, anionic and cationic surfactants enhance each other s properties (e.g., increased surface activity), show new properties (e.g., cloud point phenomena similar to nonionic surfactants), and can form different types of molecular aggregate (e.g., vesicles instead of spherical micelles). 

Inoue, T. Misono, T. (2008). Cloud point phenomena for POE-typ>e nonionic surfactants in a model room temperature ionic liquid. /. Colloid Interface Sd, 326,483-489. 

Cloud point phenomenon (cloud point extraction—CPE) Extracting analytes (both organic and inorganic) from water samples 58-65... 

Extractions Based on the Phase Separation Behavior of Aqueous Micellar Solutions. The extraction and concentration of components in an aqueous mixture can sometimes be effected via use of appropriate surfactant systems that are capable of undergoing a phase separation as a result of altered conditions (i.e. temperature or pressure changes, added salts or other species, etc.). Two general types of such surfactant extraction systems will be described (i) those based on the cloud point phenomenon and (ii) those based on coacervation formation. 

Non ionic surfactants of the poly ethoxy kted type exhibit a temperature dc-pendency that is illustrated by the so-called cloud point phenomenon. As a matter of fact, the hydrophilicity of the polyethcr chain depends on a directional interaction between each -O- atom and surrounding water molecules. As temperature increases thi.s interaction becomes looser because of the amplified randomness of the molecular motion. Hence, the hydrophilic character decreases and tin ally vanishes, as does the Am interaction. 

The existence of the cloud point phenomenon in nonionic surfactant systems carries with it a number of potential consequences—both aesthetic and functional—that must always be kept in mind. The appearance of cloudiness, while not necessarily altering the surface activity of a system, may detract from the subjective acceptability of a product. Functionally, the transition from small to large micellar aggregates may significantly alter the solubilizing... 

Alam, Md. S. Naqvi, A. Z. Kabir-ud-Din Influence of Electrolytes/Non-electrolytes on the Cloud Point Phenomenon of the Aqueous Promethazine Hydrochloride Drug Solution. /, Colloid Interface Sci, 2007, 306,161-165. 

Kim, E. J. Shah, D. O. Cloud Point Phenomenon in Amphiphilic Drug Solutions. Langmuir... 

Kumar, S. Sharma, D. Kabir-ud-Din Cloud Point Phenomenon in Anionic Surfactant + Quaternary Bromide Systems and its Variation with Additives, Langmuir, 2000,16, 6821-6824. 

Dimethicone copolyols exhibit an inverse cloud point phenomenon as an aqueous solution is heated. This same phenomenon is observed with ethoxylated fatty alcohol. The hydrogen bonding of the water with the polyoxyethylene portion of the molecule causes the cloud point. The inverse cloud point of the molecule is related to the length of the ethylene oxide chain and not the number of D units or molecular weight. The term inverse cloud point refers to the temperature at which a clear solution develops turbidity on heating. Cloud point is a phenomenon, relating to tnrbidity, which develops on cooling. 

Kumar MK, Sharma D, Khan ZA (2001) Cloud point phenomenon in ionic micellar solutions a SANS study. Langmuir 17 2549-2551... 

As straight EO nonionics, EO/PO copolymers exhibit the cloud point phenomenon. Some of them can even present a phase behavior similar to a double cloud point upon raising the temperature, after a first turbidity range, the solution becomes clearer and then turbid again. 

Kumar, S., Sharma, D., Kabir-ud-Din. Cloud point phenomenon in anionic surfactant + quaternary bromide systems and its variation with additives. Langmuir 2000, 76(17), 6821-6824. 

Changes in temperature will affect nonionic and ionic surfactants differently. In general, higher temperatures will result in small decreases in aggregation numbers for ionic surfactants but significantiy large increases for nonionic materials. The effect on nonionic surfactants is related to the cloud point phenomenon discussed previously. 

In this case, it was felt that the phenomenon would result in an inversion of the role of the material in terms of the type of emulsion favored by its presence. For example, at low temperatures a given material would be expected to be an OAV emulsifier, while at temperatures above the cloud point it would become a W/O emulsifier. In the context of emulsion technology, therefore, the cloud point phenomenon became known as the phase inversion temperature (PIT) of the surfactant and was proposed as a quantitative approach to the evaluation of surfactants in emulsion systems. In effect, the PIT is not a characteristic of a surfactant, but rather a characteristic of the complete emulsion system. 

The cloud point, usually between 0 and -10°C, is determined visually (as in NF T 07-105). It is equal to the temperature at which paraffin crystals normally dissolved in the solution of all other components, begin to separate and affect the product clarity. The cloud point can be determined more accurately by differential calorimetry since crystal formation is an exothermic phenomenon, but as of 1993 the methods had not been standardized. 

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. 

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 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. 

An interesting family of polymeric ligands show inverse temperature dependence of solubihty in water, i.e. they can be precipitated from aqueous solutions by increasing the temperature above the so-called cloud point. Typically these ligands contain poly(oxyalkylene) chains, but the phenomenon can be similarly observed with poly(N-isopropyl acrylamide) derivatives (e.g. 132) and methylated cyclodextrins, too. At or above their cloud points these compounds fall off the solution, due to the break-up and loss of the hydration shell which prevents aggregation and precipitation of their molecules. Conversely, upon cooling below this temperature (also called the lower critical solution temperature, LCST) these substances dissolve again. 

This phenomenon can be exploited for separation and concentration of solutes. If one solute has certain affinity for the micellar entity in solution then, by altering the conditions of the solution to ensure separation of the micellar solution into two phases, it is possible to separate and concentrate the solute in the surfactant-rich phase. This technique is known as cloud point extraction (CPE) or micelle-mediated extraction (ME). The ratio of the concentrations of the solute in the surfactant-rich phase to that in the dilute phase can exceed 500 with phase volume ratios exceeding 20, which indicates the high efficiency of this technique. Moreover, the surfactant-rich phase is compatible with the micellar and aqueous-organic mobile phases in liquid chromatography and thus facilitates the determination of chemical species by different analytical methods [104]. 

Fuels treated with a cloud point improver (CPI) may require additional CPI treatment whenever a wax crystal modifier is used to reduce the pour point of the fuel. Often, the cloud point of a CPI-treated fuel will increase whenever a pour point improver is used. To compensate for this phenomenon, additional CPI must be added to recover the lost performance. 

Certain cloud point improvers will disperse water into fuel and create an emulsion or haze. This phenomenon can occur at cloud point improver treat rates as low as 200 ppm. 

Nonionic surfactants tend to show the opposite temperature effect As the temperature is raised, a point may be reached at which large aggregates precipitate out into a distinct phase. The temperature at which this happens is referred to as the cloud point. It is usually less sharp than the Krafft temperature.2 The phenomenon that nonionic surfactants become less soluble at elevated temperature will be important when we discuss the phase behavior of emulsions. 

There are some similarities between third-phase formation in liquid/liquid extraction and the critical phenomenon of cloud points in aqueous solutions of nonionic polyethoxylated surfactants (12, 91). When a nonionic micellar solution is heated to a certain temperature, it becomes turbid, and by further increasing the temperature,... 

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