Contact angle hysteresis effect

The effect of thermal aging on polyethylene and isotactic polypropylene have been studied by Konar et al. [49]. They used contact angle, contact angle hysteresis, and XPS to characterize the modified surfaces of the polymers. Hysteresis increased with aging temperature. In the case of polyethylene, thermal aging led to a significant increase in adhesion strength of polyethylene with aluminium, but the increase in the case of polypropylene was much less marked. 

This same technique should be helpful in understanding wetting properties important in the oil industry since wetting is very dependent on mineral surface energies. The use of contact angle hysteresis information may allow a better understanding of the effects of surface heterogeneities of natural mineral samples. The dynamic Wilhelmy plate technique is ideally suited for such experiments ... 

With 7 = 0.072 Nm-1 and 5 = 10 nm the effective pressure is of the order of P = 72 x 10s Pa. Such a high pressure can change the surface structure, cause mechanical deformation at the moving wetting line [250], and can lead to contact angle hysteresis [251-253], especially on soft polymer surfaces. 

Fig. 6 Effect of the N/C XPS atomic concentration ratio on the contact angle hysteresis (O. ) advancing and (A,A) receding contact angles for PVC ( , ) and PC (O.A). ...

Schwartz et al. have studied this phenomenon extensively ). We may add that pore throats have a great effect, where the geometry allows meniscus curvature to vary over a greater range than that caused by contact angle hysteresis. 

The effect of roughness on the wettability of an idealized sinusoidal surface has been studied with a digital computer. The equations of Wenzel and of Cassie and Baxter are discussed in relation to the model. The heights of the energy barriers between metastable states of a drop are seen to be of utmost importance in determining the magnitude of contact angle hysteresis. 

We are not implying with this analysis that surface roughness is the only or even the most important source of contact angle hysteresis. Since it is a common source of hysteresis, it is necessary to understand the effect of roughness in order to interpret experimental results... 

Table I. Effect of pH on Contact Angle Hysteresis in Mercury-Benzene-Water System...

Since we have shown that this is not the case, we conclude that roughness cannot be the sole cause of the CLF phenomenon or of contact angle hysteresis, although there is no question that it has an effect on the measured values of these quantities. 

Fig. 9. Effect of surface chemical heterogeneity (0, = 120°, 0j = 0°) on contact angle hysteresis A, Cassie and Baxter angle, curves 1-4 represent effect of assumed energy barriers (Ref.

Recent analyses of contact angle hysteresis has treated surface heterogeneity in terms of random fluctuations see the excellent review by deGennes The approach is to treat both surface roughness and variations in surface composition as weak fluctuations, i.e. deviations from the ideally smooth surface, du/dy (Fig. 11) and from the difference in solid/liquid and solid/vapor surface energies, — yj - Both fluctuations are considered to be equivalent in perturbing the contact line and are analyzed in terms of their effect on the elastic line energy. 

The results of Johnson et al. put into some doubt the earlier concepts of surface relaxation or rearrangement effects on the dynamic contact angle. Indeed, their results suggest that in the absence of contact angle hysteresis there is no effect of velocity on... 

Besides these applications, droplet evaporation reveals several intriguing phenomena and is a prime example of a microfluidic multiphysics system, which is noticeably complex due to the interplay of mass and heat transfer, hydrodynamics of multiphase flow, interface energy effects as contact angle hysteresis, voliunetric forces as gravity, and Marangoni flows. 

Case (I) fixed contact angle 6 i) = Bo = const, R(t) variable. On smooth, ideal surfaces in the absence of any contact angle hysteresis and dynamic effects, the contact angle remains constant independent of the contact line radius, i.e., independent of the contact line position, and the radius of curvature of the interface (Fig. lb). In this case Eq. 2 can readily be integrated, thus yielding the explicit volume decrease... 

---