HS/FL system

The interactions between the hydrophobic parts of the surfactant molecules and the nonpolar liquid phases play an important role in controlling the stability of emulsions in these systems [13-20,56], While each particular system requires an individual approach, it can be concluded that the high stability of fluorocarbon annlsions against coalescence is related to a deficit in the adhesion in the HS/FL system resnlting in the sqneezing ont of hydrophobic chains from the nonpolar liquid phase. 

The rheological behavior of lAL at the interface between Pluronic aqueous solution and heptane (H S/H L system) is substantially different from that of the same Pluronic aqueous solution in contact with PFD and PFTBA (HS/FL systems). In the first case (H S/H L), the development of deformation is similar to liquid flow. In the second case (HS/FL), nonlinear solid-like behavior is observed. After some quasi-elastic... 

Stability [25-28]. However, the levels of the maxima are significantly different. These data become more illustrative and informative wheny oai values are compared at the same, reasonably low, Pluronic concentrations (Table 3.1). At F-68 concentration of 5 X 10 M, the resistance towards the coalescence of droplets for the H S/FL systems is up to two orders of magnitude higher than that for the H S/H L systems. Among the HS/FL systems, the resistance for PFTBA is more than that for PFD. 

The data obtained for model HS/FL and HS/HL systems are reported in Table 3.2 (traditionally, as F/2 values, by modulus). Differences in the F values for these two systems reach orders of magnitude. For two related phases, HS/HL, very low F values characterize the full lyophilicity. For all studied HS/FL systems, using many fluoroorganic compounds mentioned in Section 3.1, the values of F are in the range... 

Direct observations of the individual droplets of nonpolar liquids coalescence in aqueous solutions of regular and fluorinated surfactants reveal that the compressive forces ( oai) resulting in coalescence of two droplets, that is, the strength of lAL, can be much more in the case of FS/HL and HS/FL systems than for HS/HL and FS/FL ones. 

Thus, it should be stressed that interactions between hydrophobic parts of surfactant molecules and nonpolar liquid phase play a critical role in controlling the emulsion stability (Davis [2]). Of course, each particular system needs an individual approach in the quantitative evaluation of such interactions. However, we see that in the case of fluorocarbon emulsions stabilization (with respect to coalescence), the high stability relates to some deficiency in the HS/FL adhesion, when some kind of squeezing out of hydrophobic radicals from the nonpolar hquid phase can take place. 

The mechanical (rheological) studies of the considered lALs by the rotating suspension method show an essential difference between the liquid-like behavior of such layers for HS/HL and FS/FL systems and the solid-like one (manifestation of the critical shear stress, the strength) in both FS/HL and HS/FL... 

The gas densities of various parts of the system are of interest and importance to the designing engineer. If conditions of operation are such that of 100 volumes of gas leaving the converter, 20 volumes are ammonia and that 15 volumes of ammonia are removed by refrigeration there will then be 80 volumes of the gas mixture (N - + 3 FL) plus 5 volumes of ammonia to be recirculated. Since It requires 2 volumes of (N. -h 3 H.) gas to make one volume of ammonia (NHj) the 15 volumes of ammonia removed must be replaced with 30 volumes of make-up gas. The gas entering the converter will then be 115 volumes, made up of (80 -b 30) or no volumes of (Ni-f 3 Hs) gas and 5 volumes of NH3 gas. 

Figure 5 Convenient low-power laser pyrolysis system A, injection needle B, stainless steel body Cu, copper cylinder FL, flash lamp G, gas H, heater HS, heated sensor I, injector K, pyrolysis chamber LB, laser beam M, HR mirror Ma, output mirror N, Nd-GGG medium OF, optical fiber OR, O-ring P, probe PC, pumping chamber PS, power supply QC, quartz capillary S, sample Sh, shield Sw, Swagelok T, trigger V, voltage supply. (Reproduced with permission from Cecchetti W, Polloni R, Bergamasco G, et al. (1992) Journal of Analytical and Applied Pyrolysis 23 165-173 Elsevier.)...

The cohesion between the hydrophobic part of the interfacial adsorption layer and the adjacent nonpolar phase can be modeled nsing the cohesion between model hydrophobic snrfaces in the same liqnid. In snch a simnlation, the hydrophobic solid snrfaces represent the hydrophobic tails of the snrfactant molecnles. This approach allows one to overcome the difficnlties associated with the mutual solubility of the components (see Chapter 1). For the solid/liqnid/solid interface, the main parameter characterizing the interactions is the free energy of interaction, F (or Aoj), which can be established experimentally nsing Derjagnin s theorem, that is, p = %RF, where p is the cohesive force in a direct contact between two spherical particles immersed in a liqnid medinm. Snitable model systems include spherical molecularly smooth glass beads with a radius R 1-1.5 mm and hydrophobized surfaces of different natures, namely, HS and HL, immersed into the hydrocarbon and fluorocarbon liquids, HL and FL. Only dispersion forces are present in such systems, which makes the quantitative description of their interaction well defined and not complicated by the presence of various polar components. 

For such measurements, we model the considered systems as two spherical, molecularly smooth, glass particles with radius R of 1-1.5 mm, with hydrophobized surfaces methylated surfaces, simulating hydrophobic parts of HS, and fluorinated surfaces, simulating hydrophobic part of FS, in various hydrocarbon and fluorocarbon media (HL, FL). Practically, only dispersion interactions take place in these systems, making their quantitative consideration particularly definite - uncomplicated by combination with various polar components [16, 31, 32]. The cohesion force p between these two particles is measured by a device based on the magneto-electric dynamometer, similar to the apparatus used in experiments with droplets [15, 23, 33]. 

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