Contact Angle dynamic advancing

Angle to the main flow direction Surface coverage Advancing contact angle Dynamic contact angle Receding contact angle Density Eluid density Residual... 

The Wilhelmy slide has been operated in dynamic immersion studies to measure advancing and receding contact angles [59] (see Chapter X). It can also... 

When spontaneous spreading occurs, the bulk of the advancing liquid is preceded by a precursor film, usually a few millimeters in width and a few hundred nanometers or less in thickness [58], as pictured in Fig. 12. The observed dynamic contact angle is that which is made by the bulk liquid against the precursor film, and it itself depends on the rate of the advance of the nominal interline. The relationship between the rate of spontaneous spreading, i.e. the rate of movement of the nominal interline normal to itself, (/, and the dynamic contact... 

Polyelectrolyte Multilayers" Dynamic Contact Angle Advancing Contact Angle... 

In addition to the methods discussed here and in Section 6.2, there are a few other methods for measuring surface tension that are classified as dynamic methods as they involve the flow of the liquids involved (e.g., methods based on the dimensions of an oscillating liquid jet or of the ripples on a liquid film). As one might expect, the dynamic methods have their advantages as well as disadvantages. For example, the oscillating jet technique is ill-suited for air-liquid interfaces, but has been found quite useful in the case of surfactant solutions. A discussion of these methods, however, will require advanced fluid dynamics concepts that are beyond our scope here. As our primary objective in this chapter is simply to provide a basic introduction to surface tension and contact angle phenomena, we shall not consider dynamic methods here. Brief discussions of these methods and a comparison of the data obtained from different techniques are available elsewhere (e.g., see Adamson 1990 and references therein). 

Figure 7.12 Some geometries used to study the dynamics of contact angle phenomena (A) spreading drop, (B) liquid advancing in a capillary, (C) plate, tape or fibre immersed in a liquid, and (D) rotating cylinder in a pool of liquid.

Dynamic advancing and receding contact angles can be measured by moving the plate up or down. It may be possible to choose a rate in a range such that the position of the line of contact is essentially independent of rate, about I mm/min or less. The motion can. of course, be stopped and the angle measured after a specified time. 

ADSA-P has been employed in various surface tension and contact angle studies, including static (advancing) contact angles [69.70], dynamic (advancing) contact angles at slow motion of the three-phase contact line [4, 71—74], and contact angle kinetics of surfactant solutions [75]. A schematic of the experimental setup for ADSA-P sessile drops is shown in Fig. 6. More details are available elsewhere [66[. 

Contact angles were calculated from the profile of the water as it was advanced or receded over the surface for dynamic values or from the stationary drop for static values. 

Similar to static contact angles from the sessile droplet method, Wilhelmy dynamic contact angles are an excellent indication of the change in surface characteristics due to surface modification techniques such as plasma polymerization coating. The cosine of dynamic advancing contact angles from the first immersion, cos 0D,a,i of untreated, TMS-treated, and (TMS-I-02)-treated conventional... 

Figure 26.13 The effects of plasma treatment on wettability, which is given by the cosine of the dynamic advancing contact angles, cos 0d calculated from the first immersion FjL lines of each force loop dotted lines indicate the mean cos 0D,a,i of TMS and TMS+O2 treated polymers.

Cosines of dynamic advancing and receding contact angles, cos 0D,a and cos 0D r, were plotted as a function of the cosine of static contact angles cos 0s on all untreated and plasma-treated polymers in Figure 26.19. As expected, cos 0o,a was smaller and cos 0d i. was larger than cos 0s. Since dynamic contact angles are dependent on the velocity of immersion/emersion, a constant speed of 5 mm/min was selected to emphasize the major aspect of wettability. 

Figure 26.20 A correlation between the average of dynamic advancing and receding contact angles from the Wilhelmy method and static advancing contact angles from the sessile droplet method for untreated, TMS and TMS + O2 treated pol5rmers follows the relationship given by cos 6s = (cos 0u, .,i + cos 0D,a,i)/2.

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