Surfactant hydration

Impurities (including surfactants, hydrates, solvates, complexes, and reactive additives) can greatly inLuence the rate of dissolution by modifying the crystal habit or by interfering with the interfacial transport of solute from the crystal to the bulk solution. 

FIG. 3 a-Chymotrypsin solubility (protein concentration) in reverse micelles of 0.1 M AOT in octane, as a dependence on the degree of surfactant hydration (water-to-AOT molar ratio), for protein molecules with chemically modified surface groups. ( ) Acetyl-a -ch5miotrypsin (O) succinyl-a-chymotrypsin (—) maximal concentration of nonmodified native a -ch5miotrypsin solubilized in reverse micelles. 

FIG. 5 Regulation of relative maximal reaction rates (F/Kopt) for different enz5mes solubilized in AOT reverse micelles by variation of the degree of surfactant hydration (water-to-AOT molar ratio). The inset shows the correlation between the radius of an entrapped enzyme (fp) and corresponding optimal aqueous micellar cavity (v). (For details see Ref. 40.)... 

A protein molecule is entrapped in the inner cavity of a reverse micelle the size of which may vary with variation in the degree of surfactant hydration. Normally, simple proteins (enzymes) form protein-containing micelles in a stoichiometric ratio of 1 1. It is, in some cases, possible to entrap a larger amount of protein in one micelle when using extremely high (> 10 mM) protein concentrations [31]. 

Solutions of water-containing reversed micelles are systems characterized by a multiplicity of domains apolar bulk solvent, oriented alkyl chains of the surfactant, hydrated surfactant headgroup region at the water/surfactant interface, and bulk water in the micellar core. Many polar, apolar, and amphiphilic substances, which are preferentially solubilized in the micellar core, in the bulk organic solvent, and in the domain comprising the alkyl chains and the hydrated surfactant polar heads, henceforth referred to as the palisade layer, respectively, may be solubilized in these systems at the same time. Moreover, it is possible that (1) local concentrations of solubilizate are very different from the overall concentration, (2) molecules solubilized in the palisade layer are forced to assume a certain orientation, (3) solubilizates are forced to reside for long times in a very small compartment (compartmentalization, quantum size effects), (4) the structure and dynamics of the reversed micelle hosting the solubilizate as well as those of the solubilizate itself are modified (personalization). 

Despite this donble complexity, it is possible to use enzymes in surfactant solutions to get a deeper insight in their structure and dynamics. In this chapter, we showed that enzymes can yield useful information on surfactant hydration, interfacial film rigidity, and partitioning of cosurfactants. Enzymes are also useful as an independent check for pH in reverse microemulsions. We could also show that for some of the properties of microemulsions such as cosurfactant partition coefficients, semi-qnantitative results can be obtained. 

Uses Lubricant, surfactant, hydrator, detackifier, profoamer, and softener in personal care such as hair sprays, hand lotions, antiperspirants, roll-ons, shaving preps, shampoos, conditioners, foundations, creams, gels/setting lotions Properties Cl, to hazy, colorless liq. sol. in water sp.gr, 1,07 vise. 200-650 cS Toxicology Prolonged contact with skin, eyes may cause some irritation nonhaz-ardous with a very low order of toxicity... 

The bound water freezes at a lower temperature than the interphasal water, which is just another way of sa5dng that the surfactant-water interaction is stronger for the bound water. However, the interphasal water-surfactant hydrate is, of course, more stable because if the positive entropic contribution (to the formation of ordered crystals in the freezing process) is overcompensated in the case of bound water at a lower temperature than in the case of interphasal water, then the bound water will obviously melt at this lower temperature. For simplicity, we assume here that no supercooling occurs. Clearly, the argument also remains essentially the same when supercooling does occur. 

Microscopic sheets of amorphous silica have been prepared in the laboratory by either (/) hydrolysis of gaseous SiCl or SiF to form monosilicic acid [10193-36-9] (orthosihcic acid), Si(OH)4, with simultaneous polymerisation in water of the monosilicic acid that is formed (7) (2) freesing of colloidal silica or polysilicic acid (8—10) (J) hydrolysis of HSiCl in ether, followed by solvent evaporation (11) or (4) coagulation of silica in the presence of cationic surfactants (12). Amorphous silica fibers are prepared by drying thin films of sols or oxidising silicon monoxide (13). Hydrated amorphous silica differs in solubility from anhydrous or surface-hydrated amorphous sdica forms (1) in that the former is generally stable up to 60°C, and water is not lost by evaporation at room temperature. Hydrated sdica gel can be prepared by reaction of hydrated sodium siUcate crystals and anhydrous acid, followed by polymerisation of the monosilicic acid that is formed into a dense state (14). This process can result in a water content of approximately one molecule of H2O for each sdanol group present. 

Mucolytics reduce the viscosity of tenacious and purulent mucus, thus faciUtating removal. The distinction between mucolytics and other classes of expectorants is frequently blurred. Steam, sometimes in conjunction with surfactants or volatile oils, has long been used to decrease viscosity by physical hydration. However, agents that chemically depolymerize certain components of mucus are available. Trypsin and other proteolytic enzymes have shown good clinical activity because of their abiUty to cleave glycoproteins. Pancreatic domase, which depolymerizes DNA found in purulent mucus, also has shown clinical utihty. 

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 dodecyl sulfate has been used to induce a dry, scaly skin condition in human subjects by daily treatment with a 4% aqueous solution on one leg over a period of 2 weeks. Measurements were made of stratum comeum hydration, scaliness, and lipid composition which were used to assess in vivo surfactant perturbations on desquamation [381]. 

The colloid probe technique was first applied to the investigation of surfactant adsorption by Rutland and Senden [83]. They investigated the effect of a nonionic surfactant petakis(oxyethylene) dodecyl ether at various concentrations for a silica-silica system. In the absence of surfactant they observed a repulsive interaction at small separation, which inhibited adhesive contact. For a concentration of 2 X 10 M they found a normalized adhesive force of 19 mN/m, which is small compared to similar measurements with SEA and is probably caused by sufactant adsorption s disrupting the hydration force. The adhesive force decreased with time, suggesting that the hydrophobic attraction was being screened by further surfactant adsorption. Thus the authors concluded that adsorption occurs through... 

FIG. 4 Onion model of spherical water-containing reversed micelles. Solvent molecules are not represented. A, surfactant alkyl chain domain B, head group plus hydration water domain C, hulk water domain. (For water-containing AOT-reversed micelles, the approximate thickness of layer A is 1.5 nm, of layer B is 0.4 nm, whereas the radius of C is given hy the equation r = 0.17R nm.)... 

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