Interface disk/water

FIG. 4 ir—A isotherms measured for DSPC at water-1,2-DCE (O) and water-air ( ) interfaces from Ref. 41 and simulated with a real gas model [40] ideal gas with A = 0 and Ug = 0 (thin solid line), hard disks gas with A = 40 and ug = 0 (thick solid line), vdW gas with = 40 and Ug/kT = 3 (thin dashed line), and vdW gas with = 40 A and UgjkT = 7 (thick dashed line). The inset shows part of the thick dashed line. (Reproduced from Ref 40 with permission from Elsevier Science.)... 

For all three types of dendrimers described above, a flattened, disk-like conformation was observed for the higher generations. However, the molecular shape at the air-water interface is also intimately associated with the polarity, and hence the type of dendrimer used. In case of the polypropylene imine) and PAMAM dendrimers the hydrophilic cores interact with the sub-phase and hence these dendrimers assume an oblate shape for all generations. The poly(benzyl ether) dendrimers, on the other hand, are hydrophobic and want to minimize contact with the water surface. This property results in a conformational shape change from ellipsoidal, for the lower generations, to oblate for the higher generations [46]. 

A dished head tank of diameter DT = 1.22 m is filled with water to an operating level equal to the tank diameter. The tank is equipped with four equally spaced baffles whose width is one-tenth of the tank diameter. The tank is agitated with a 0.36-m-diameter, flat, six-blade disk turbine. The impeller rotational speed is 2.8 rev/s. The sparging air enters through an open-ended tube situated below the impeller, and its volumetric flow, Q, is 0.00416 m3/s at 25°C. Calculate the following the impeller power requirement, Pm gas holdup (the volume fraction of gas phase in the dispersion), H and Sauter mean diameter of the dispersed bubbles. The viscosity of the water, //, is 8.904 x 10 4 kg/(m-s), the density, p, is 997.08 kg/m3, and, therefore, the kinematic viscosity, v, is 8.93 x 10 7 m2/s. The interfacial tension for the air-water interface, a, is 0.07197 kg/s2. Assume that the air bubbles are in the range of 2-5 mm diameter. 

Lin et al. [17] studied the dynamics of copolymers adsorbed on an air-water interface. These measurements complemented the static measurements described above and in Fig. 4. The extent of the polymer films perpendicular to the surface is small compared to penetration distance and wavelength so that EWDLS is most sensitive to variation of composition in the plane of the interface. Figure 7 shows the measured normalized autocorrelation I (/) for different surface pressures. Frames a-d were taken during the first compression of the monolayer, and frames e-h were taken during the second compression. The difference between the two sets of measurements is an indication of structural changes induced by compression cycling. The frames e-g can be compared to the data in Fig. 4. The solid lines in the three frames are fits to a sum of two exponential functions, each with a characteristic decay time. The fast decay constant has a characteristic associated with diffusive motion of the disks. The slow decay constant ( several seconds) was ascribed to the dynamics of the associations of disks. 

Hotta et al. [38] have developed a new electrochemical device for studying ET at the O/W interface, in which the O and W phases are separated by an electron conductor (e.g., Pt). This system is named as electron-conductor separating oil-water (ECSOW) system. As shown in Figure 8.3, the EC phase that separates the O and W phases can be feasibly realized by connecting two platinum disk electrodes with an electric wire. 

Laity and Treybal (LI) report on experiments with a variety of two-phase systems in a covered vessel which was always run full, so that there was no air-liquid interface at the surface of the agitated material. Under these circumstances no vortex was present, even in the case of operation without baffles. Mixing Equipment Company flat-blade disk-turbines were used in 12- and 18-in. diameter vessels whose heights were about 1.07 times their diameters. Impeller diameter was one-third of tank diameter in each case. For operation without baffles, using only one liquid phase, the usual form of power-number Reynolds-number correlation fit the data, giving a correlation curve similar to that given in Fig. 6 for disk-turbines in unbaffled vessels. In this case, however, the Froude number did not have to be used in the correlation because of the absence of a vortex. For two-phase mixtures, Laity and Treybal could correlate the power consumption results for unbaffled operation by means of the same power number-Reynolds number correlation as for one-phase systems provided the following equations were used to calculate the effective mean viscosity of the mixture For water more than 40% by volume ... 

M.E. Schrader, J, Colloid Interface Sci, 27 (1969) 743 SD using goniometer eye piece smooth, fused silica disk (a) in absence of water, (b) water vapour admitted. 

Fig. 4 Single radial disk turbine placed at oil-water interface. (From Ref.. )...

As previously discussed, placing a radial disk or Rush-ton turbine in the aqueous or lower phase, close to the interface, can be effective when making oil-in-water dispersions. A central interfacial vortex forms with the commencement of impeller motion. This directs a stream of the lighter oil phase to the impeller where it disperses. The volume of the oil layer decreases with continued dispersion until it is exhausted. Placing the turbine in the oil or upper phase, close to the interface, can result in water-in-oil dispersions, because a water-containing vortex forms, allowing water to be dispersed into the lighter oil phase. 

Another model for understanding the diffusion of lipopolymers at the air-water interface in Region II is the free area model, useful for describing the motion of phospholipids on a Langmuir monolayer and many systems where the diffusing particles can be approximated by hard spheres, disks or cylinders [38], In this model, a particle can diffuse in any direction that is free, or in other words, in any direction that is empty of another particle. As would be expected, more crowded or concentrated systems diffuse more slowly. Assuming the particles are at a constant temperature and that other energetic considerations can be described within a constant, D0, this type of diffusion can be expressed as... 

The second approach is based on using a microprobe to perturb equilibrium in one of the phases near the interfacial boundary. The transfer of electrochemically active ions and neutral molecules across the liquid/liquid interface can be studied with a metal tip positioned near the phase boundary (56). The interfacial flux was induced by using a disk-shaped UME to deplete the concentration of transferred species in one of two phases. The transfer processes at an air/water and hydrogel/solution interfaces can be studied similarly (56). 

Figure 2 Comparison of the surface rheology of casein and lysozyme at the n-hexadecane—water interface (10 wt % protein, pH 1, 0.005 M, 25 °C). The logarithm of the angular rotation rate U> (of the dish) is plotted against the logarithm of the torque X (on the disk) , o, casein (duplicate runs, 8 h old, If - 3.55 0.05 mN m"l s) , A, casein (duplicate runs, 50 h old, = 12.6 0.1 mN m l s) , lysozyme ( = 0.55 N m l s). Dashed line represents Newtonian behavior (slope = 1) solid line represents highly non-Newtonian behavior (slope 9).

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