Overflowing cylinder

Overflowing cylinder. In this apparatus the deformation of the interface is purely dilational. The liquid under investigation is pumped from below to the top of a vertical cylinder, where it is allowed to flow over the top rim and downwards along... 

Figure 3.73. Schematic representation of the overflowing cylinder technique (a) side view, (b) top view, indicating the radial velocity u (r). (Courtesy of A. Prins et al.)...

Various experimental methods for dynamic surface tension measurements are available. Their operational timescales cover different time intervals. - Methods with a shorter characteristic operational time are the oscillating jet method, the oscillating bubble method, the fast-formed drop technique,the surface wave techniques, and the maximum bubble pressure method. Methods of longer characteristic operational time are the inclined plate method, the drop-weight/volume techniques, the funnel and overflowing cylinder methods, and the axisym-metric drop shape analysis (ADSA) " see References 54, 55, and 85 for a more detailed review. 

The overflowing cylinder data indicate also a difference in structure of the adsorbed protein layers at pH 3 and 6.7. Glycinin was able to stop radial expansion of the surface at low length of the falling film L at both pH s. However Lstlll, above which the adsorbed protein film breaks, and a radial expansion of the surface was observed, was clearly higher at pH 3 than at pH 6.7, 2.3 and 1.9 cm, respectively. This indicates that the 3S/7S form of glycinin is able to form a... 

Although many other experimental set-ups were developed to study the dynamics of adsorption, mainly via surface and interfacial tensions, of solutions of surface active compounds and polymers, they cannot all be described in detail here. More are given in textbooks of surface chemistry, e.g. by Adamson (1990) or Edwards et al. (1991). The last original technique, briefly discussed in this chapter, is the overflowing cylinder method used for example by Bergink-Martens et al. (1990). 

Fig. 5.24 Sketch of the overflowing cylinder set-up, according to Bergink-Martens et al. (1990)...

Future developments will also focus on the combination of different techniques, such as drop pressure and drop shape methods. A more efficient approach would be to combine macroscopic with microscopic or molecular methods, for example drop shape or pressure experiments with ellipsometric or spectroscopic techniques. Another useful possibility involves linking, for example, the inclinded plate or overflowing cylinder technique with scattering experiments, which would allow studies of structure formation under dynamic conditions and at freshly formed surfaces (Howe et al. 1993). 

FIG. 7 Foamability (a) as measured by means of the closed loop foam generator at three different gas flow rates and surface expansion rates (b) as measured by the overflowing cylinder technique as a function of the alcohol activity for butanol solutions. The arrow indicates the limit of solubility. (From Ref. 80.)... 

The case of adsorption at an interface that is subjected to stationary expansion needs a special theoretical description. This case is experimentally realized with the strip method [95,116], and the overflowing cylinder method [60,92]. It could be realized also by a Fangmuir trough. The interfacial expansion is characterized by the quantity d = dAI(Adt), which represents the relative rate of... 

This special case of interfacial dynamics is realized with the strip method [95,147] and the overflowing cylinder method [60,92]. Because the adsorption process is stationary, the time, t, is not a parameter of state of the system. For this reason, in the kinetic diagrams (like Figure 4.10) we plot the perturbations versus the dimensionless rate of surface expansion, 0 = (h /Di)(dA/dt)/A, where A is the interfacial area, and dA/dt = constant is the interfacial expansion rate. In Figure 4.10, the total perturbations, 4i,t> 4c,r, plotted, which represent the local perturbations, 4i(z), 4<.(z),... 

There is a now an array of experimental techniques that can be used to measure d5mamic surface tensions, y(t), including maximum bubble pressure (MBP), oscillating jet, inclined plate, drop volume, drop shape, and overflowing cylinder (OFC).i With the aid of an appropriate equation of state, it is possible to infer the d5uiamic surface excess, F(0. Uncertainty in the adsorption isotherm can lead to problems in the interpretation of DST data and incorrect conclusions as to the adsorption mechanisms. A more direct approach is to measure ( ) itself by neutron reflection (NR), or ellipsometry. ii Here we review the state of the art, with particular attention to recent results on model single-chain cationic surfactants... 

Figure 8.2 (a) The overflowing cylinder (OFC). (b) Schematic setup of the OFC with neutron reflection. Slits - SI, S2, S3, S4. M -incident beam monitor. D - flnal detector. Reprinted with permission from [16]. (2003) American Chemical Society. 

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