Contact angle hysteresis, surface

Superhydrophobicity, polyurethane, contact angle hysteresis, surface reorganization... 

SOME COMPLICATIONS IN THE ESTABLISHMENT OF THE CONTACT ANGLE HYSTERESIS, SURFACE HETEROGENEITY, AND ROUGHNESS... 

S. Moradi, S. G. Hatzikiriakos, and P. Englezos, Contact angle hysteresis Surface morphology effects. Colloid Polym. Sci. 291, 317-328 (2012). 

It is clear from our discussion of contact angle hysteresis that there is some degree of variability in reported contact angle values. The data collected in Table X-2, therefore, are intended mainly as a guide to the type of behavior to be expected. The older data comprise mainly results for refractory and relatively polar solids, while newer data are for polymeric surfaces. 

Fig. 13. Molion of a liquid interline across a sharp edge, (a) Close-up of movement over the sharp edge show.s that the liquid must exhibit the appropriate contact angle against the surface in front of it in order to advance over the edge, (b) Contact angle hysteresis resulting from the sharp edge.

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. 

It has been shown that contact angle hysteresis might arise as a result of inhomogeneities of the surface wetted by the liquid phase or surface roughness [70]. When surface roughness plays a considerable role, the observed contact angle may depend on the exact position of the contact line with respect to the microscopic or... 

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 ... 

The MAMs were found to be closely packed. NEXAFS and FTIR spectroscopy studies revealed that the molecular tilting angles relative to the surface normal varied from 4° to 21° as a function of Ax. In wetting studies it was found that the highest water contact angles ( 131°) with the lowest contact angle hysteresis... 

However, no matter how rough the surface, the forces will be the same as those that exist between a solid and a liquid. The surface roughness may show contact angle hysteresis if one makes the drop move, but this will arise from other parameters (e.g., wetting and dewetting). Further, in practice, the surface roughness is not easy to define. A fractal approach has been used to achieve a better understanding (Feder, 1988 Birdi, 1993). 

An informative model for contact angle hysteresis is obtained by postulating the surface... 

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. 

Contact angle hysteresis can be caused by surface roughness, heterogeneity, dissolved substances, and structural changes of the solid at the three-phase contact line. 

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