The inclined plate technique

Another method applicable over longer times, from 50 ms up to seconds, is the so-called inclined plate (IP) method developed by Van den Bogaert Joos (1979). A surfactant solution is allowed to flow over an inclined plate with an angle of inclination a. The solution is pumped over the plate and the flow rate is measured by the rotameter. The surface tension of the solution surface, freshly formed at the inlet, is measured by using a Wilhelmy plate oriented with its length parallel to the flow direction. The schematic of the set-up is shown in Fig. 5.22. 

From the measured surface tension as a function of the distance from the inlet, adsorption kinetics data are obtained by recalculating the effective age of the surface at a distance x. Due to an analysis of the flow pattern and the effect of surface tension gradients on it given by Hansen (1964) the effective age is calculated from the surface velocity of the flowing liquid v by X, =x/v.  

An analysis of the complex problem of liquid flow and adsorption kinetics was given by Ziller et al. (1985) (cf. Section 4.8). The system of linearised hydrodynamic and transport equations was solved numerically under the assumption of different boundary conditions. The results show that a quantitative interpretation of inclined plate experiments requires a time consuming analysis. However, a rather good approximation is possible by neglecting the Marangoni flow induced by surface tension gradients against the flow direction. 

The inelined plate technique is applicable to liquid/gas interfaces only. Temperature eontrol seems to be very complicated. As the time is also limited to a small interval of 25 ms up to a few seconds, the application of this method is restricted only to some special cases. However, the eomparison of experimental results of the inclined plate technique with those obtained by other methods exhibits good agreement (Van Hunsel Joos 1987a, Fainerman et al. 1993a, Miller et al. 1994b, d). 

Description of Other Dynamic Methods for Interfacial Studies 

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In the studies to which we have referred, the adhesive interaction of particle aggregates with the surface was determined by the inclined-plate technique (see Section 11). 

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