Lyotropic salts

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). 

Ammonium sulfate is frequently used as lyotropic salt to promote hydrophobic interaction. It is also known that in the presence of this salt, antibodies tend to precipitate (see Section IV.D.i) and share their water content with the solid phase with consequent association. This is a dual mechanism where each phenomenon contributes for the adsorption of the antibody on an hydrophobic resin and has been frequently used for purification of antibodies from different sources.106-109... 

The asymmetric polyamide membranes were prepared using a casting solution consisting of 15 g polymer, 85 g DMAC and 35 wt 2 LiNO, (bop) as the lyotropic salt. Salt concentrations in the casting solution are conveniently expressed as percent based on polymer (BOP). The doped polyamide solution was cast on a Pyrex glass plate using a 25-mil doctor knife. The film was then partially dried to obtain a gel membrane of polymer/solvent/salt. The air side (skin side) was identified and the gel film immersed in ice water. After an hour in ice water, the membrane was transferred to distilled water and stored until it was tested. 

In addition to DMAC, the solvents DMF, DMSO and UMP can be used for casting aromatic polyamide membranes. Lyotropic salts that give good polyamide membranes are those with lithium, calcium and magnesium as the cation and chloride, bromide, iodide, nitrate, thiocyanate and perchlorate as the anion. 

The extensive research on microemulsions was prompted by two oil crises in 1973 and 1979, respectively. To optimise oil recovery, the oil reservoirs were flooded with a water-surfactant mixture. Oil entrapped in the rock pores can thus be removed easily as a microemulsion with an ultra-low interfacial tension is formed in the pores (see Section 10.2 in Chapter 10). Obviously, this method of tertiary oil recovery requires some understanding of the phase behaviour and interfacial tensions of mixtures of water/salt, crude oil and surfactant [4]. These in-depth studies were carried out in the 1970s and 1980s, yielding very precise insights into the phase behaviour of microemulsions stabilised by non-ionic [5, 6] and ionic surfactants [7-9] and mixtures thereof [10]. The influence of additives, like hydro- and lyotropic salts [11], short- and medium-chain alcohols (co-surfactant) [12] on both non-ionic [13] and ionic microemulsions [14] was also studied in detail. The most striking and relevant property of micro emulsions in technical applications is the low or even ultra-low interfacial tension between the water excess phase and the oil excess phase in the presence of a microemulsion phase. The dependence of the interfacial tension on salt [15], the alcohol concentration [16] and temperature [17] as well as its interrelation with the phase behaviour [18, 19] can be regarded as well understood. 

In Fig. 10.12(a), the phase behaviour in the short float is shown. The three-phase state of the respective systems is located near the degreasing temperature T = 30°C. Efficient degreasing is a result of the ultra-low interfacial tension between water and fat. Upon diluting the short float with pure water the salt mass fraction in the water phase is effectively reduced from e = 0.21 to e = 0.07. Sodium chloride belongs to the group of lyotropic salts. When the salt mass fraction is reduced the hydration of the surfactant head... 

It should be mentioned that lyotropic salts, such as ammonium sulfate and potassium phosphate, have a thermoprotective effect on enzymes that rivals the effect of organic solutes in vitro. However, it is unlikely that these salts could play a role in vivo, since the large concentrations required for protection would interfere with enzyme activity and metabolic regulation, and have, in fact, never been found... 

Pinna MC, Salts A, Monduzzi M, Ninham BW (2005) Hofmeister series the hydrolytic activity of Aspergillus niger lipase depends on specific anion effects. J Phys Chem B 109 5406-5408 PoUlon WN, Betties JF (1979) Deoxygenated sickle hemoglobin. Effects of lyotropic salts on its solubility. J Bio Chem 254 3462-3467... 

Rather than fix the water/salt ratio as a brine pseudocomponent, another useful possibility is to fix the alcohol/ionic surfactant ratio as the pseudo-component (fix 8) and vary the salt concentration. An increase of the lyotropic salt concentration in ionic surfacant plus alcohol cosurfactant systems has the same effect as increasing temperature or salt in nonionic surfactant mixtures - a lipophilic shift is observed, and the phase behaviour progresses from 2 to 3 to 2 (15). If salt is placed in the position occupied previously by the cosurfactant in Figure 4.8, and the fixed ratio of alcohol/ionic surfactant placed as a combined pseudocomponent (fixed 5) at the surfactant position, at equal amounts of oil and water (a = 0.5) a plot of salt concentration (e) versus overall cosurfactant/surfactant concentration (y) also yields a fish -shaped phase diagram (45). Therefore, in either the case of fixed salt concentration (fixed ) or the case of fixed alcohol/ionic surfactant ratio (fixed 8), the optimally formulated microemulsions for the chosen fixed ratio of 8 or s, are found at X, where the tail and body of the fish meet (see Figure 4.8). Consequently, the phase behaviour of simple monodisperse ethoxylated alcohol surfactants in oil and water qualitatively mimics that of much more complicated mixtures containing ionic surfactants, cosurfactants and salt. Alcohol... 

Salt concentration, lyotropic Salt concentration, lyotropic Salt concentration, hydrotropic Alcohol cosurfactant concentration Nonionic polymer concentration Surfactant block copolymer concentration... 

Measurement of ligand-binding by proteins or peptides Study of lyotropic salt effects in hydro-phobic chromatography... 

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