Hysteresis, of contact angle

The large hysteresis of contact angle, together with the noticeable influence of drying on the contact angle, suggests that the density of graft dextran chains at the EVAL surface... 

An effect foimd by Jamin, that a chain of air bubbles in a capillary tube separated by short water columns can sustain a finite pressure, is not shown when the apparatus is quite clean and is due to hysteresis of contact angles caused by a trace of grease. ... 

Houllevigue s formula for latent heat of evaporation in capillary tube, 369 Huggins s molar volume formula, 21 hydrogen bonds, 3, 41 hydrometer, 14 Nicholson s, 14 hydrostatic balance, 14 pressure and vapour pressure, 367 hydroxyl bonds, 41 hylotropic phases, 229 hyperbola, 421, 423 hyperbolic paraboloid, 431 hyperboloid, 429, 430 hysteresis of contact angle, 166... 

Hysteresis of Contact Angles in the System Mercury - Benzene - Water... 

Current theories to explain hysteresis of contact angles are primarily based on the concepts of surface roughness, surface heterogeneity, friction, and adsorption phenomena. Unintentional adsorption, or contamination—the result of inadequate experimental technique—is, however, the most frequent explanation. As all systems involving solids are subject to the reasons indicated above for hysteresis, we chose the system mercury-benzene-water, which should be affected only by adsorption phenomena, controllable under proper experimentation. An additional advantage is the fact that all interfacial tensions involved can be measured. 

Hysteresis of contact angles is a practical complication all the above discussion ignored hysteresis. On very smooth, homogeneous, rigid solids, with slow movement of the liquid-vapor front, hysteresis is small. It is not yet known whether a truly hysteresis-free system of a liquid on a bulk polymer, with 0 > 0, exists. The lowest hysteresis observed by the author with a polymeric solid is of the order of 2 degrees. (A method of silicone treatment for glass, which yields a surface on which hysteresis is reported to be zero, has been described by Neumann et. al. and by Hertzberg et.al.. )... 

Bartell FE, Shepard JW (1953) Surface roughness as related to hysteresis of contact angles. 11. The systems of paraffin-3 molar calcium chloride solution-air and paraffin-glycerol-air. J Phys Chem 57 455 58... 

Bartell FE, Shepard JW (1953) Surface roughness as related to hysteresis of contact angles. 

BarteU FE, Bjorldund CW (1952) Hysteresis of contact angles. A study of interfacial contact angles in the mercury-benzene-water system. J Phys Chem 56 453-457... 

However, there is a phenomenon that is far more important than the previous ones from a practical point of view. It is called the static hysteresis of contact angle. 

It is usnally believed that the static hysteresis of contact angle is determined by the surface roughness and/or heterogeneity (Figure 1.15). 

Figure 1.15b presents the magnified vicinity of the three-phase contact line of the same droplet as in Figure 1.15a. This picture gives a qualitative explanation of the phenomenon of the static hysteresis of contact angle, which is widely adopted in the literature. The static hysteresis of contact angle is connected with multiple equilibrium positions on the drop edge on a rough surface. No doubt...

In earlier studies [5], a completely new concept of hysteresis of contact angle on smooth homogeneous substrates has been suggested. This mechanism will be discussed in Section 3.10. In the following, we give a qualitative description of this phenomenon. 

Static Hysteresis of Contact Angles from Microscopic Point of View Surface Forces... 

At this stage, we are capable of explaining the nature of the hysteresis of contact angles via the S-shape of the isotherm of disjoining pressure (curve 2 in Figure 1.12) in the case of partial wetting. More details are given in Section 3.10. 

First of all, we recall what the hysteresis of contact angle in capillaries means. Let us consider a meniscus in the case of partial wetting in a capillary (Figure 1.18a and Figure 1.18b). Note that the capillary is in contact with a reservoir where the pressure, - P, in the reservoir is lower than the atmospheric pressure, P. ... 

In the case of equilibrium liquid drops and menisci (see Section 2.3), they are supposed to be always at equilibrium with flat films with which they are in contact with in the front. Only the capillary pressure acts inside the spherical parts of drops or menisci, and only the disjoining pressure acts inside thin flat films. However, there is a transition zone between the bnlk liquid (drops or menisci) and the thin flat film in front of them. In this transition zone, both the capillary pressure and the disjoining pressure act simultaneously (see Section 2.3 for more details). A profile of the transition zone between a meniscus in a flat capillary and a thin a-fllm in front of it, in the case of partial wetting, is presented in Figure 2.5. It shows that the liquid profile is not always concave but changes its curvature inside the transition zone. Just this peculiar liquid shape in the transition zone determines the static hysteresis of contact angle (see Chapter 3)... 

It is important to recall that the aforementioned value of the line tension can be used only at equilibrium. It is impossible to experimentally measure the equilibrium liquid droplets on sohd substrates because they should be at equilibrium with oversaturated vapor, as was explained in Section 2.3. This would mean that usually everything in Equation 2.193 is either far from equilibrium or under a quasi-equilibrium condition (as caused by the hysteresis of contact angle — see Section 3.10). In that case, the value of line tension can be many orders of magnitude higher than 10 -10- dyn. However, this line tension should be referred to as dynamic line tension. To the best of our knowledge, there has not been any attempt as yet to introduce or investigate the dynamic line tension. 

According to the definition of line tension (2.222), it is determined by the equilibrium liquid profile in the transition region from the thin flat liquid interlayer to the bulk surface of bubbles. Note that in the case of partial wetting, which is under consideration, the static hysteresis of contact angle (see Chapter 3, Section 3.10) is unavoidable. The latter phenomenon can substantially influence the comparison. 

Further consideration shows that the initial state as well as the presence or absence of the film in front (zone 3 in Figure 3.28b) does not influence our consideration. That is, the same consideration as below can be applied to the static hysteresis of contact angle on initially dry surface. 

The fundamental conclusion of this section is the relation of the mechanism of static hysteresis of contact angle of smooth homogeneous surfaces to the form of the disjoining pressure isotherm. It should be noted that static hysteresis of the nature considered appears not only on smooth homogeneous surfaces but also on heterogeneous ones. Thus, in actual cases, the possibility of the simultaneous appearance of static hysteresis phenomena of different natures must be taken into consideration. 

Next, results are presented on measurements of static advancing and static receding contact angles on smooth nonporous nitrocellulose substrate for different SDS concentrations. The idea is to compare hysteresis of contact angles on the smooth nonporous nitrocellulose substrate with the hysteresis contact angles obtained earlier on porous nitrocellulose substrates at corresponding SDS concentrations. 

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