Cloud point electrolytes

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. 

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. 

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... 

The effect of electrolytes and drugs on the cloud point of hydroxypropylmethylcellulose gels and the dissolution of drugs from hydroxypropylmethylcellulose matrix tablets... 

This paper reports the effect of pH, electrolytes and drugs on the cloud points of HPMC gels and the effect of these electrolytes on the dissolution of propranolol hydrochloride from HPMC matrices and on the disintegration of HPMC matrices containing no drug. 

Although HPMC is not thought itself to be pH sensitive [6], the pH of a dissolution fluid is known to affect release rates of drugs from its matrices via the suppression of ionization [7]. The cloud points at 2% K100 gels (Table 1) were only affected by pH at low pHs. It was therefore considered unnecessary to modify the pH of electrolyte solutions used to determine cloud points. 

Drug release profiles from the tablets in various dissolution media are shown in Fig. 2. In all cases the release rates decreased initially from the control (distilled water) as electrolyte concentration increased, until a minimum release rate was obtained. As the electrolyte concentration further increased the release rates similarly increased until a burst release occurred. These initial decreases in release rates were probably coincident with a decrease in polymer solubility, in that as the ionic strength of the dissolution medium is increased the cloud point is lowered towards 37°C. It may be seen from Table 5 that minimum release rates occurred when the cloud point was 37°C. At this point the pore tortuosity within the matrix structure should also be at a maximum. It is unlikely to be an increase in viscosity that retards release rates since Ford et al. [1] showed that viscosity has little effect on release rates. Any reduction in hydration, such as that by increasing the concentration of solute in the dissolution media or increasing the temperature of the dissolution media, will start to prevent gelation and therefore the tablet will cease to act as a sustained release matrix. 

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. 

Marszall, L. 1988. Cloud point of mixed ionic-nonionic surfactant solutions in the presence of electrolytes. Langmuir4 90-93. 

Nonionic surfactants dissolve in aqueous solutions through hydrogen bonding between the water molecules and the oxyethylenic portion of the surfactant. These interactions are weak but enough in number to maintain the molecule in solution up to the cloud point temperature, at which the surfactant separates as a different phase (4). Figure 3 shows that electrolytes like calcium chloride, potassium chloride, or sodium chloride reduce the cloud point of Triton X-100. Hydrochloric acid instead promoted a salting-in effect similar to that observed for ethanol. 

The electrolyte effect of some water-soluble monomers on the cloud point of ethoxylated surfactants is illustrated in Figure 4. In the absence of salt, the cloud point of the emulsifier blend (6 1086 Arlacel 83, HLB = 9.3) is equal to 64°7 ( ). Three monomers-sodium acrylate, MADQUAT - ADQUAT (acryloxyethyltrimethylammonium chloride) - salt the surfactant blend out, the strongest effect being observed with ADQUAT ( 9). 

Also reported for comparison are the curves relative to two non polymerizable salts, sodium acetate and sodium chloride which cause a salting out of the surfactant. The role of electrolytes in the stabilization of the polymerized systems will be discussed below. The cloud point shift values, for the surfactant blend, measured after addition of a unimolal electrolyte solution are listed in Table II. 

Figure 4.29. Cloud point of 5 x 10" M Cj2Ey influence of added electrolytes md urea. (Redrawn eifter K. Deguchi, K. Meguro. J. Colloid Interface Set 50 (1972) 223.)...

We have examined the stmcture of both ionic and nonionic micelles and some of the factors that affect their size and critical micelle concentration. An increase in hydrophobic chain length causes a decrease in the cmc and increase of size of ionic and nonionic micelles an increase of polyoxyethylene chain length has the opposite effect on these properties in nonionic micelles. About 70-80% of the counterions of an ionic surfactant are bound to the micelle and the nature of the counterion can influence the properties of these micelles. Electrolyte addition to micellar solutions of ionic surfactants reduces the cmc and increases the micellar size, sometimes causing a change of shape from spherical to ellipsoidal. Solutions of some nonionic surfactants become cloudy on heating and separate reversibly into two phases at the cloud point. 

Non-ionics are characterised by its cloud point. It is the temperature at which 1.0% solution of non-ionic surfactants, become cloudy or insoluble. The larger the number of ethylene oxide molecules in the product, higher is the cloud point. The exception to this rule is a non-ionic that is co-reacted or capped, with propylene oxide. Another method of overcoming the problem of cloud point is to blend the non-ionic with an anionic such as a soap, a sulphonate or a phosphate. The cloud point of non-ionic surfactant solution can be depressed by the addition of an electrolyte like common salt, Glauber s salt etc. 

As the addition of electrolytes reduces the PIT, an emulsifier with a higher PIT value will be required when preparing emulsions in the presence of electrolytes. Electrolytes cause dehydration of the PEO chains which, in effect, reduces the cloud point of the nonionic surfactant this must be compensated for by using a surfactant with a higher HLB. The optimum PIT of the emulsifier is fixed if the storage temperature is fixed. 

Citrate compounds are salting-out electrolytes — they tie up water molecules in the liquid and as a result help force the formation of liquid crystals or lamellar stmctures. It is sometimes possible to reverse this trend by the addition of salting-in electrolytes, compounds with high lyotropic numbers (>9.5) which can raise the cloud point of a liquid formulation [26], This permits increased concentration without the onset of structuring. 

The addition of neutral electrolyte to solutions of nonionic POE surfactants increases the extent of solubilization of hydrocarbons at a given temperature in those cases where electrolyte addition causes an increase in the aggregation number of the micelles. The order of increase in solubilization appears to be the same as that for depression of the cloud point (Section IIIB, below) (Saito, 1967) K+ > Na+ > Li+ Ca2+ > Al3+ SO4 > Cl-. The effect of electrolyte addition on the solubilization of polar materials is not clear. 

The incidence of the ability of salts to reduce the hydration of compressed hydrophilic matrices has been investigated by some authors [90,95]. The disintegration times of plain HPMC 2208 (15 000 mPa s grade) tablets in various solutions of electrolytes could be correlated with the cloud points (Table 19). 

In summary, we demonstrated that it is possible to carry out reactions in W/CO2 microemulsions catalyzed by water soluble organometallic complexes. The microemulsions were stable in the presence of several electrolytes and the cloud points were not affected even at high electrolyte concentrations. In the future, we would like to investigate the factors controlling activity and selectivity and determine the feasibility of a catalyst recovery and recycle system based on such a microemulsion system. 

One limitation of the HLB concept is its failure to account for variations in system conditions from that at which the HLB is measured (e.g., temperature, electrolyte concentration). For example, increasing temperature decreases the water solubility of a nonionic surfactant, ultimately causing phase separation above the cloud point, an effect not captured in a temperature-independent HLB value. When both water and oil are present, the temperature at which a surfactant transitions from being water soluble to oil soluble is known as the phase inversion temperature (PIT). Below the PIT, nonionic surfactants are water soluble, while above the PIT. they are oil soluble. Thus, from Bancroft s rule, a nonionic surfactant will form an 0/W emulsion below its PIT and a W/0 emulsion above its PIT. Likewise, increasing salt concentrations reduces the water solubility of ionic surfactant systems. At elevated salt concentrations, ionic surfactants will eventually partition into the oil phase. This is illustrated in Fig. 13. which shows aqueous micelles at lower salt concentrations and oil-phase inverse micelles at higher salt concentrations. Increasing the system temperature will likewise cause this same transition for nonionic surfactant systems. 

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