Silica aqueous solutions

Fig. 4. Schematic representation of the adsorbed layer of Ci2E6 at the silica-aqueous solution interface.

Sakai, K. et al.. Adsorption characteristics of zwitterionic diblock copolymers at the silica/aqueous solution interface. J. Colloid Interf. Sci., 317, 383, 2008. 

Furlong, D.N., Adsorption of tris(2,2-bipyridine)ruthenium(ll) cations at silica/ aqueous solution interfaces, Aust. J. Chem., 35, 911, 1982. 

Adhesion Tension Measurements for Silica-Aqueous Solutions of LNBr. Adhesion tensions had previously been measured for such systems by Guastalla [14]. 

An aging effect for the measured force, f, was observed for the systems studied by Tenebre [26] and myself [29]. After the slide had been lifted 0.5 mm., f decreased and attained a stable value, which was used in tracing the wetting cycles (Figure 4). The adhesion tensions for the systems silica-aqueous solutions of LNBr and silica-alkaline solutions (1.2 X 10 M NaOH) of LNBr were measured at 24° C. and plotted as a function of the concentration of LNBr (Figure 5,a and b). For these systems the chemical adsorption is known (Figure 3 and Table I). 

Figure 5. Emersion and immersion adhesion tensions for silica-aqueous solutions of LNBr as a function of LNBr concentration in solution 24° C,...

The constant of integration in Equation 4 was adjusted by using the average value, Tgxp, obtained from the receding and advancing adhesion tensions at c lne = 10 M. Then the calculated curve for the adhesion tension silica-aqueous solutions of LNBr is obtained (Figure 5,a). This curve verifies the experimental results satisfactorily. 

Adsorption and Tension at Silica-Aqueous Solution Interface... 

D.N. Furlong, J.R. Aston, Adsorption of polyoxyethylated nonyl phenols at silica/aqueous solution interfaces. Colloids Surf. 1982,4,121-129. 

Until recently, the fast rate at which a surfactant layer forms at the solid-liquid interface has prevented accurate investigation of the adsorption process. As a result, the mechanism of surfactant adsorption has been inferred from thermodynamic data. Such explanations have been further confused by misinterpretation of the equilibrium morphology of the adsorbed surfactant as either monolayers or bilayers, rather than the discrete surface aggregates that form in many surfactant-substrate systems.2 However, the recent development of techniques with high temporal resolution has made possible studies of the adsorption, desorption,25>38,4i,48-6o exchange rates of surfactants. In this section, we describe the adsorption kinetics of C ,TAB surfactants at the silica-aqueous solution interface, elucidated by optical reflectometry in a wall-jet flow cell. The adsorption of C jTAB surfactants to silica is the most widely studied system - and hence the adsorption kinetics can be related to the adsorption process with great clarity. For a more thorough review of adsorptions isotherms, the t5q)es of surfactant structures that form at the solid-liquid interface, and the influence of these factors on adsorption, the reader is directed to Reference 24. 

Figure 8.16 Adsorption process for cationic surfactants at the silica-aqueous solution interface. Each span is described in the text. Reprinted with permission from [24]. (2003) Elsevier.

Figure Bl.20.8. DLVO-type forces measured between two silica glass surfaces in aqueous solutions of NaCl at various concentrations. The inset shows the same data in the short-range regime up to D = 10 mn. The repulsive deviation at short range (<2 nm) is due to a monotonic solvation force, which seems not to depend on the salt concentration. Oscillatory surface forces are not observed. With pemiission from [73].

This is an acid-base reaction, in which the base is the oxide ion (p. 89) the acidic oxide SiOj displaces the weaker acidic oxide CO2 in the fused mixture. But in aqueous solution, where the 0 ion cannot function as a strong basefp. 89),carbon dioxide displaces silica, which, therefore, precipitates when the gas is passed through the aqueous silicate solution. In a fused mixture of silica and a nitrate or phosphate, the silica again displaces the weaker acidic oxides N2O5 and P4OJ0 ... 

Anhydrous hydrogen fluoride (as distinct from an aqueous solution of hydrofluoric acid) does not attack silica or glass. It reacts with metals to give fluorides, for example with heated iron the anhydrous iron(II) fluoride is formed the same product is obtained by displacement of chlorine from iron(II) chloride ... 

In reverse-phase chromatography, which is the more commonly encountered form of HPLC, the stationary phase is nonpolar and the mobile phase is polar. The most common nonpolar stationary phases use an organochlorosilane for which the R group is an -octyl (Cg) or -octyldecyl (Cig) hydrocarbon chain. Most reverse-phase separations are carried out using a buffered aqueous solution as a polar mobile phase. Because the silica substrate is subject to hydrolysis in basic solutions, the pH of the mobile phase must be less than 7.5. 

Unloaded silica does not recover HPA from aqueous solution. The surface of silica gel modified with quarternary ammonium salts (QAS) gets anion-exchange properties. The aim of the work is the elaboration of solid-phase reagents on the base of ion associate of HPA with QAS immobilized onto silica surface for the determination of phosphoms and organic reductants. Heterocyclic (safranine and lucigenine) and aliphatic (trinonyloctadecyl ammonium iodide and tetradecyl ammonium nitrate) compounds have been examined as QAS. 

The worked out soi ption-photometric method of NIS determination calls preliminary sorption concentration of NIS microamounts from aqueous solutions on silica L5/40. The concentrate obtained is put in a solution with precise concentration of bromthymol-blue (BTB) anionic dye and BaCl, excess. As a result the ionic associate 1 1 is formed and is kept comparatively strongly on a surface. The BTB excess remains in an aqueous phase and it is easy to determinate it photometrically. The linear dependence of optical density of BTB solutions after soi ption on NIS concentration in an interval ITO - 2,5T0 M is observed. The indirect way of the given method is caused by the fact the calibration plot does not come from a zero point of coordinates, and NIS zero concentration corresponds to initial BTB concentration in a solution. 

Aqueous solutions of dyes ean also be employed instead of water. In the ease of hydrophilic dyes such as methylene blue or patent fast blue the transparent background of the TLC/HPTLC plate is stained blue. Pale spots occur where there are nonwetted zones. Dauble [89] detected anion-active detergents in this way on silica gel layers as pale zones on a blue background with palatine fast blue GGN... 

Note The reagent can be employed on silica gel and cellulose layers. When derivatization is carried out from the vapor phase the detection limit for morphine is 10 ng and that for papaverine 1 ng per chromatogram zone [5]. In some cases it has been recommended that ammonium sulfate be added to the layer with subsequent heating to 150 —180 °C [1] after derivatization. It is also possible to spray afterwards with an aqueous solution of potassium iodide (1 %) and starch (1%) [2]. 

To a stirred solution of 2,3-dimethyl indole (6, 1.45 g, 10 mmol, 1.0 equiv) and tetra-n-butylammonium sulfate (3.40g, 10 mmol, 1.0 equiv) in chloroform (150 mL) was added potassium hydroxide (50% aqueous solution, 20 mL) over 30 minutes. The stirring was continued for six hours, at which time the mixture was extracted with chloroform, the chloroform-water mixture was washed with water, and the organic layer concentrated. Silica gel chromatography provided 2,4-dimethyl-3-chloroquinoline (7, 1.52 g, 79% yield). 

Preparation of cholesta-5,7-diene-ia,3/3-diol a solution of 500 mg of the 1,4-cyclized adduct of cholesta-5,7-dien-3/3-ol-ia,2a-epoxideand 4-phenyl-1,2,4-triazoline-3,5-dione in 40 ml of tetrahydrofuran is added dropwise under agitation to a solution of 600 mg of lithium aluminum hydride in 30 ml of THF. Then, the reaction mixture liquid Is gently refluxed and boiled for 1 hour and cooled, and a saturated aqueous solution of sodium sulfate is added to the reaction mixture to decompose excessive lithium aluminum hydride. The organic solvent layer is separated and dried, and the solvent Is distilled. The residue Is purified by chromatography using a column packed with silica gel. Fractions eluted with ether-hexane (7 3 v/v) are collected, and recrystallization from the methanol gives 400 mg of cholesta-5,7-diene-la, 3/3-diol. 

Synthesis of 16,16-dimethyl-trans-A -PGEi 2.35 g of the bis-tetrahydropyranyl ether were dissolved in 6 ml of tetrahydrofuran and 60 ml of 65%-acetic acid aqueous solution and the solution stirred at 60°C to 70°C for 20 minutes. The reaction mixture was extracted with ethyl acetate, and the organic layer was washed with water, dried and concentrated under reduced pressure. The residue was purified by column chromatography on silica gel using ethyl acetate-cyclohexane (2 3) as eluent to yield 270 mg of the title compound. 

Figure 15 High-surface area silica treated with aqueous solution of 1 wt% vinyltrimethoxy silane. A silica was polymerized with styrene and washed with CS2 three times. Polystyrene produced in experiment A was deposited with B silica and the silica washed with CS2 three times. (From Ref. 77.)...

The need for temperature cycling should be taken into account when designing or conducting tests. The nature of the test vessel should be considered for tests in aqueous solutions at temperatures above about 60°C since soluble constituents of the test vessel material can inhibit or accelerate the corrosion process. An inhibiting effect of soluble species from glass, notably silica, on the behaviour of steel in hot water has been shown . Pure quartz or polymeric materials are often more appropriate for test vessel construction. 

The drawback of the described adsorbents is the leakage of the bonded phase that may occur after the change of eluent or temperature of operation when the equilibrium of the polymer adsorption is disturbed. In order to prepare a more stable support Dulout et al. [31] introduced the treatment of porous silica with PEO, poly-lV-vinylpyrrolidone or polyvinylalcohol solution followed by a second treatment with an aqueous solution of a protein whose molecular weight was lower than that of the proteins to be separated. Possibly, displacement of the weakly adsorbed coils by the stronger interacting proteins produce an additional shrouding of the polymer-coated supports. After the weakly adsorbed portion was replaced, the stability of the mixed adsorption layer was higher. 

Alpert has shown [47] that poly(succinimide)-silica can be further hydrolyzed to poly (aspartic acid)-silica or condensed with [3-alanine in aqueous solution to form a covalently bonded copolymer of 2-carboxyethyl aspartamide and aspartic acid. The content of carboxyl groups generated by this way has not been quantified directly, but the cation-exchange hemoglobin capacity has been measured for a series of the packings. Thus, the optimal concentration of poly(succinimide) used in the synthesis was found to be 2 5%. 

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