Slow solubilization

It was observed that the NIR-predicted monomer concentration varied greatly during the first 45 minutes after monomer addition but then stabihzed this was attributed to slow solubilization of large monomer droplets into the water phase, and slow partition of monomer between the water phase and the latex phase, leading to large local variations in monomer concentration. This was avoided by allowing a 60-minute soak period after monomer addition, before the temperature was increased to start the polymerization. 

Bourlat et al. (1995) have presented results on the plutonium radioactivity levels in Mururoa lagoon water during the 1985-1991 period. The low radioactivity levels recorded, from 0.01 to 1.5 Bq/m are due to the slow solubilization of plutonium deposited in lagoon sediments following atmospheric experiments which took place from 1966 to 1974. The average concentrations of the lagoon water decrease from one year to the next. Since the Mururoa lagoon is open to the ocean, plutonium radioactivity traces are also detectable in the immediate vicinity of the atoll. 

The fibrin indicator gel was prepared as outlined in the schematic (Fig. 1) and as described previously (R4, R5). Briefly, plasminogen-rich fibrinogen was slowly solubilized at a concentration of 5mg/ml in 0.85% (w/v) saline (prewarmed to 37 °C) with gentle mixing (inversion several times over 1.5-2 h) in a temperature-controlled water bath at 37 °C. Slow solubilization of fibrinogen was necessary to prevent protein flocculation. Agarose was separately prepared as a 1% (w/v) solution in phosphate-buffered saline (PBS, pH... 

With C12E5 as the nonionic surfactant at a 1 wt% level in water, quite different phenomena were observed below, above, and well above the cloud point when tetradecane or hexadecane was carefully layered on top of the aqueous solution. Below the cloud point temperature of 31 °C, very slow solubilization of oil into the one-phase micellar solution occurred. At 35 C, which is just above the cloud point, a much different behavior was observed. The surfactant-rich L phase separated to the top of the aqueous phase prior to the addition of hexadecane. Upon addition of the oil, the L, phase rapidly solubilizes the hydrocarbon to form an oil-in-water microemulsion containing an appreciable amount of the nonpolar oil. After depletion of the larger surfactant-containing drops, a front developed as smaller drops were incorporated into the microemulsion phase. This behavior is shown schematically in Figure 12.16. Unlike the experiments carried out below the cloud point temperature, appreciable solubilization of oil was observed in the time frame of the study, as indicated by upward movement of the oil-microemulsion interface. Similar phenomena were observed with both tetradecane and hexadecane as the oil phases. 

Chloroacetyl chloride [79-04-9] (CICH2COCI) is the corresponding acid chloride of chloroacetic acid (see Acetyl chloride). Physical properties include mol wt 112.94, C2H2CI2O, mp —21.8 C, bp 106°C, vapor pressure 3.3 kPa (25 mm Hg) at 25°C, 12 kPa (90 mm Hg) at 50°C, and density 1.4202 g/mL and refractive index 1.4530, both at 20°C. Chloroacetyl chloride has a sharp, pungent, irritating odor. It is miscible with acetone and bensene and is initially insoluble in water. A slow reaction at the water—chloroactyl chloride interface, however, produces chloroacetic acid. When sufficient acid is formed to solubilize the two phases, a violent reaction forming chloroacetic acid and HCl occurs. 

In a multiphase formulation, such as an oil-in-water emulsion, preservative molecules will distribute themselves in an unstable equilibrium between the bulk aqueous phase and (i) the oil phase by partition, (ii) the surfactant micelles by solubilization, (iii) polymeric suspending agents and other solutes by competitive displacement of water of solvation, (iv) particulate and container surfaces by adsorption and, (v) any microorganisms present. Generally, the overall preservative efficiency can be related to the small proportion of preservative molecules remaining unbound in the bulk aqueous phase, although as this becomes depleted some slow re-equilibration between the components can be anticipated. The loss of neutral molecules into oil and micellar phases may be favoured over ionized species, although considerable variation in distribution is found between different systems. 

Figure 10 shows the sequence of chemical and physical effects leading to coal solubilization under mild conditions. The first step in the conversion involves catalyst-coal contacting a slow rate of contacting may limit the effective reactivity of the catalytic medium. The nature of the... 

The uses of micelles in chemical analysis are rapidly increasing (Hinze, 1979). Analytical reactions are carried out typically on a small scale and are based on spectrophotometry. At the same time, undesired side reactions can cause major problems, especially when the analytical procedure depends on reactions which are relatively slow and require high temperatures, exotic solvents or high reagent concentrations for completion. Micelles can suppress undesired reactions as well as speed desired ones and they also solubilize reagents which are sparingly soluble in water. In addition it is often possible to make phosphorescence measurements at room temperature in the presence of surfactants which enormously increases the utility of this very sensitive method of detection. 

Soil components, silica, and alumina are solubilized, in low concentration, and can react, or crystallize, to form new clays. In addition, clays from any source change over time and become simpler and simpler. Silica is more soluble than alumina and so the silica alumina ratio decreases over time. Eventually, this leads to deposits of alumina that are used as an aluminum ore for the production of aluminum metal. Although these reactions are considered to be very slow on a human timescale, they do occur. 

In this equation, the value of (Red) is a function of the nature of the reductant, its solubility, the crystallinity of solid phases containing it, effects of solubilizing agents, transport limitations, and other factors. Likewise the value of (Ox) is a function of various factors. As discussed in the previous chapter, most redox reactions are very slow and the prevailing conditions are therefore sensitive to catalysis. Three types of catalysis are involved ... 

The reason for these differences is not well known but it is interesting to speculate. The lower HLB surfactants tested are also those with the shortest hydrophilic chains, and so the smallest molecular areas (10). They should therefore have the highest concentrations at the LDL2 surface at saturation causing disruption and solubilization. The slow action of 012 23 could be due to slow replacement of 0 2 23 molecules by lower HLB impurities in the surfactant samples. 

In vitro enzymatic polymerizations have the potential for processes that are more regio-selective and stereoselective, proceed under more moderate conditions, and are more benign toward the environment than the traditional chemical processes. However, little of this potential has been realized. A major problem is that the reaction rates are slow compared to non-enzymatic processes. Enzymatic polymerizations are limited to moderate temperatures (often no higher than 50-75°C) because enzymes are denaturated and deactivated at higher temperatures. Also, the effective concentrations of enzymes in many systems are low because the enzymes are not soluble. Research efforts to address these factors include enzyme immobilization to increase enzyme stability and activity, solubilization of enzymes by association with a surfactant or covalent bonding with an appropriate compound, and genetic engineering of enzymes to tailor their catalytic activity to specific applications. 

The vesicular size might go back reversiblly to the original one in the case of nonionic vesicles (Figures 9 and 10) for which the present removal rate may be too slow. A similar behavior was reported by Schurtenberger et al. for their lecithin-bile salt systems vesicle size is reduced to the original dimension after dialysis of remains large when the solubilized is diluted with the buffer solution to very fast reduction of bile salt fast removal of bile salt(22) ... 

Let s go back to much simpler systems, for example the self-aggregation of surfactant molecules. When surfactant molecules solubilize in water, often the process is slow at the very beginning, and gets faster with time the more surface bilayer is formed, the more the process speeds up, because there is more and more active surface where the next steps of aggregation can take place. The same... 

When CTAC is solubilized in micellar solution with sulfide S2- ions, at low water contents (w < 10), the presence of CTAC induces a strong decrease in CdS nanocrystallite size. For a given water content, the absorption spectra are blue shifted when the syntheses are performed in the presence of CTAC compared to that obtained in its absence. The temporal evolution of absorption at 250 nm is approximated to nucleation rate of CdS. It slows down in the presence of CTAC. This blue shift is more pronounced at low water content and high CTAC concentration. Hence it is observed a decrease in the particle size by increasing CTAC concentration. This can be related to the decrease in the intermicellar potential in the presence of CTAC (64). 

The nucleation rate is slowed down with increasing CTAC concentration, notably at a water content w equal to 3. However, this phenomenon is less important compared to what is obtained previously by solubilizing CTAC in micellar solution with sulfide S2 ions. 

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