Pendent drop experiment

Fig. 5.17 Schematic of a video enhanced pendent drop experiment according to Cheng et al. (1990)...

In the pendent drop experiments, the surrounding temperature is easily controlled by using a small quartz cuvette. The cuvette can be sealed during the measurements to avoid evaporation effects. This makes the pendent drop technique particularly suited for measurements of very... 

One of the variants of the technique involves a pendent drop on a conical tip. The reason for experimenting with this geometry is to reduce drop vibrations, always a source of error if high accuracy is required. Sessile drops and pendent drops on inclined surfaces have been investigated by Nguyen et al. ) and by Lawal and Brown ), respectively. For such systems the drops are no longer axis)rm-metric. 

In the present chapter current relaxation theories will be described first both damping of harmonically generated disturbances and relaxations to transient perturbations. Thereafter, experiments are described, based on the damping of capillary and longitudinal waves, oscillation behaviour of bubbles. Also transient relaxations with pendent drop and drop and bubble pressure measurements are shown. Finally, applications to different interfaces, using surfactants, surfactant mixtures, polymers and polymer/surfactant mixtures are discussed. 

Fig. 6.7 Video enhanced pendent drop method modified for relaxation experiments according to Miller et al. (1993a)...

Transient relaxation experiments of protein adsorption layers were published by Miller et al. (1993a, c, d). The experiments were performed using a modified pendent drop technique described in Section 6.3.4. The surface tension response to three subsequent square pulse perturbations of 0.1 mg/ml HA adsorbed at the aqueous solution/air interfaces (Miller et al. 1993a) are shown in Fig. 6.21. 

The pendent drop technique has also been extended to studies of insoluble monolayers of phospholipids at the water/n-dodecane interface (Li et al. 1994b). In these experiments first a monolayer is produced on a water drop surface as described above. Then, the water drop is gently immersed into the second liquid, for example n-dodecane. Then the change of the drop size enables one to compress and expand the interfacial film. Again, the isotherm obtained with ADSA shows the same type of dynamic behaviour as measured with the classic Langmuir-Blodgett trough technique (Thoma Mohwald 1994). 

Harmonic and transient relaxation experiments for dodecyl dimethyl phosphine oxide solutions were performed with the elastic ring method by Loglio [240]. This methods allows oscillation experiments in the frequency range from about 0.5 to 0.001 Hz and is suitable for comparatively slow relaxing systems. Slow oscillation experiments can be performed much easier now with the pendent drop apparatus [186]. Both techniques are also able to perform transient relaxation experiments. The two types of experiments have a characteristic frequency defined in the same way by Eq. (4.110). 

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