Decane droplets

The same apparatus was used to measure the kinetics of emulsion crystallization under shear. McClements and co-workers (20) showed that supercooled liquid n-hexadecane droplets crystallize more rapidly when a population of solid n-hexa-decane droplets are present. They hypothesized that a collision between a solid and liquid droplet could be sufficient to act as a nucleation event in the liquid. The frequency of collisions increases with the intensity of applied shear field, and hence shearing should increase the crystallization rate. A 50 50 mixture of solid and liquid n-hexadecane emulsion droplets was stored at 6 -0.01 °C in a water bath (i.e., between the melting points and freezing points of emulsified n-hexadecane). A constant shear rate (0-200 s ) was applied to the emulsion in the shear cell, and ultrasonic velocities were determined as a function of time. The change in speed of sound was used to calculate the percentage solids in the system (Fig. 7). Surprisingly, there was no clear effect of increased shear rate. This could either be because increase in collision rate was relatively modest for the small particles used (in the order of 30% at the fastest rate) or because the time the interacting droplets remain in proximity is not affected by the applied shear. 

Fig. 14.4 Dependence of interdroplet flow propagation speed on interdroplet spacing, measured in microgravity experiments fm a linear array of n-decane droplets in standard atmosphere [15]...

Figure 6. Right Experimental and calculated transmission spectra of decane droplets dispersed in water using SDBS as surfactant. Left Number and weight particle size distribution obtained for this liquid-liquid dispersion system.

FIG. 11 Crystallization thermogram for the mixed emulsion containing 15 wt% n-hexa-decane droplets and 15 wt% tetradecane droplets. 

Fig. 6.4 Plots of (a) snap-in force versus advancing contact angle and (b) weight loss of the hexa-decane droplet after puU off versus receding contact angle with different surfaces (reproduced with...

As an example figure B 1.14.13 shows the droplet size distribution of oil drops in the cream layer of a decane-in-water emulsion as determined by PFG [45]. Each curve represents the distribution at a different height in the cream with large drops at the top of the cream. The inset shows the PFG echo decay trains as a fiinction of... 

Figure Bl.14.13. Derivation of the droplet size distribution in a cream layer of a decane/water emulsion from PGSE data. The inset shows the signal attenuation as a fiinction of the gradient strength for diflfiision weighting recorded at each position (top trace = bottom of cream). A Stokes-based velocity model (solid lines) was fitted to the experimental data (solid circles). The curious horizontal trace in the centre of the plot is due to partial volume filling at the water/cream interface. The droplet size distribution of the emulsion was calculated as a fiinction of height from these NMR data. The most intense narrowest distribution occurs at the base of the cream and the curves proceed logically up tlirough the cream in steps of 0.041 cm. It is concluded from these data that the biggest droplets are found at the top and the smallest at the bottom of tlie cream.

Several researchers have measured the absorption rate at the presence of dispersed organic phase [1,17-18,37,39,49,51-53]. Bruining et al. [37] measured the oxygen absorption in stirred vessels with plane interface in the presence of small amounts of decane, hexadecane, c = 0.01 - 0.1 while van Ede et al. [49] applied octene as a dispersed phase. Littel et al.[39] used carbon dioxide for absorption in dispersion of toluene droplets with c = 0 - 0.4. The theoretical data in the literature were mostly verified by the experimental results of the above... 

Two main microemulsion microstructures have been identified droplet and biconti-nuous microemulsions (54-58). In the droplet type, the microemulsion phase consists of solubilized micelles reverse micelles for w/o systems and normal micelles for the o/w counterparts. In w/o microemulsions, spherical water drops are coated by a monomolecular film of surfactant, while in w/o microemulsions, the dispersed phase is oil. In contrast, bicontinuous microemulsions occur as a continuous network of aqueous domains enmeshed in a continuous network of oil, with the surfactant molecules occupying the oil/water boundaries. Microemulsion-based materials synthesis relies on the availability of surfactant/oil/aqueous phase formulations that give stable microemulsions (54-58). As can be seen from Table 2.2.1, a variety of surfactants have been used, as further detailed in Table 2.2.2 (16). Also, various oils have been utilized, including straight-chain alkanes (e.g., n-decane, /(-hexane),... 

The experimental data of Espiard et al. (21,22), based on the AOT/ toluene/water/ammonia system, showed an increase in particle size with increase in R. This observation led the authors to conclude that the droplet size of the microemulsion water pool was a key determinant of particle size. The effect of R on particle size was also investigated for silica nanoparticles synthesized in AOT/ decane/water/ammonia microemulsions (31). No particles were observed below about R = 4. However, as R increased from 5 to 9.5, the particle size also increased, in agreement with the observations of Espiard et al. (21,22). As noted previously (see Figure 2.2.3), in this microemulsion system, free water pools do not become... 

Influence of Intermicellar Interactions. By replacing isooctane by cyclohexane as the bulk solvent, the intermicellar potential decrease inducing a decrease in the exchange micellar rate by a factor of 10 (24,63) whereas with decane the exchange micellar rate increases by a factor of 2 (27). The size of the droplets remains the same by replacing the bulk solvent. 

At high water content, w > 10, by using Cd(N03)2 as a reactant, the size of the particles increases with the change of the bulk solvent as follows cyclohexane, isooctane, decane. Hence, at a given droplet size (w = constant), the increase in the intermicellar potential induces an increase in the average diameter of the particles. 

Tsapkina, E., Semenova, M., Pavlovskaya, G., Leontiev, A., Tolstoguzov, V. (1992). The influence of incompatibility on the formation of adsorbing layers and dispersion of n-decane emulsion droplets in aqueous solution containing a mixture of 11S globulin from Viciafaba and dextran. Food Hydrocolloids, 6, 237-251. 

Since one of the issues raised in this paper is whether the objects seen in the TEM images are a proper representation of the structures present in solution, we will describe briefly sample preparation strategies. For solutions of micelles in hexane, a very volatile solvent, samples for TEM studies could be obtained by aspirating a dilute solution directly onto a carbon-coated copper grid. Most of the solvent likely evaporated as the sample was deposited on the substrate. Alternatively, the TEM substrate could be dipped briefly into a dilute solution of the micelles and allowed to dry. This method also worked for less volatile solvents like decane. For decane, we could also place a small drop (a few pi) of solution on the grid and then touch the edge of the droplet with a Kimwipe to remove excess solvent. For several samples these methods were compared, and we observed the same morphology. 

We have developed new reaction systems based on colloidal dispersions [23, 24], namely highly concentrated water-in-oil (gel) emulsions, which could overcome most of the disadvantages of the aqueoussolvent mixtures such as inactivation of the aldolase and incomplete aldehyde solubilization in the medium. These emulsions are characterized by volume fractions of dispersed phase higher than 0.73 [25] therefore, the droplets are deformed and/or polydisperse, separated by a thin film of continuous phase. Water-in-oil gel emulsions of water/Ci4E4/oil 90/4/6 wt%, where C14E4 is a technical grade poly(oxyethylene) tetradecyl ether surfactant, with an average of four moles of ethylene oxide per surfactant molecule and oil can be octane, decane, dodecane, tetradecane, hexadecane, or squalane, were typically chosen as reaction media [23, 26]. 

The thickness of horizontal filns of n-decane sandwiched between two water (or aqueous electrolyte) droplets has been determined by a light reflectance technique. The films were stabilised by three surfactants an xyx block copolymer of poly(ethyleneoxide) and poly(12-hydroxystearic) acid soya bean lecithin Arlacel 83 (sorbitan sesquioleate). Results obtained for two and three component mixtures of the surfactants were compared with those for the single surfactants. The results showed that, provided sufficient polymer is present in the film, the thickness is determined by the longest oleophilic chain, namely the poly(12-hydroxystearic) acid. 

Single Surfactant Systems. Relative intensity results for an equilibrium film of the block copolymer B1 in n-decane sandwiched between two water droplets at 25°C, are shown in Table II. The intensity was independent of the bulk polymer concentration within the accuracy of measurement. Assuming a constant film refractive index this implies that the film thickness is independent of surfactant concentration, and an average value of J was used for the calculation of film thickness. Coalescence occurs below a concentration of 0.1 g dm, presumably because there is insufficient... 

Electrolyte in the Aqueous Phase. Measurements in the presence of ammonium nitrate showed the film thickness to be independent of electrolyte concentration up to 0.0625 mol dm-. Unfortunately measurements could not be made at high concentration due to distortion of the upper droplet. The presence of electrolyte in the aqueous phase would not in fact be expected to affect significantly the thickness of a decane film of low relative permittivity. 

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