Interfacial energetics wetting

From the above, it is obvious that good wetting does not necessarily mean a thermodynamically strong interface good wetting means that the interfacial bond is energetically nearly as strong as the cohesion bond of the liquid itself. 

It can be derived from Antonow s rule, 15.7.4], applying it to partial wetting but accounting for the adhesion between solid and liquid, assuming it to be dominated by the Van der Waals, or dispersion, parts of the surface tensions, y and y. Various studies have shown that [5.7.5] is quite effective for materials that mainly interact through dispersion forces and that it remains a reasonable approximation for systems in which other interactions also operate. The root in the r.h.s. of [5.7.5] stems from the assumption that Berthelot s principle may be applied. In sec. 2.11b we argued that this principle may be applied only to the energetic part of the interfacial tensions and that a more correct form is... 

The wetting of a surface can be described in thermodynamic terns. Important parameters that could have an effect on adhesion development and the interfacial bond include the surface energetics of both the sohd coating and the substrate as well as the surface tension of the coating in its liquid state (Lee, 1991 KendaU, 2001). The spreading coefficient, which is related to the surface tension, defines the capabUity of a liquid to wet and spread on a sofid. The surface teision of both substances (fiquid and sofid) will determine whether a given coating will wet a sofid surface. 

Several papers by Kendall treated the subject of adhesion rather explicitly with simple models of mechanics. Andrews and Kinloch attempted to separate "adhesion" and "adhesive joint strength" and established that the intrinsic failure energy is close to the work of adhesion when pure interfacial failure occurs. Kloubek attributed the interaction of polar forces to the contribution of the work of adhesion. The effect of surface energetics and wetting on adhesion has been summarized by Kaelble, Mittal, and Zisman . ... 

Figures 4.13 and 4.14 show that these dependencies are linear (with an exception of low density polyethylene). The slopes of lines are proportional to the thickness of the surface layer, 8, i.e., they increase together with the energy of interfacial interaction. Also, the experimental data for a polyamide-6-fumed silica system, show correlation between the value of K and the heat of wetting of the filler by polar liquids. In some cases, the extrapolation of the dependence to W/(l - W) = 0 leads to values of a > 1 (Figure 4.14). It means that the same filler may, at low content, act as an initiator of crystallization, increasing the crystallinity degree, or prevent crystallization at higher concentrations because of the transformation of a majority of pol5aner chains in surface layers and increase of energetic barrier of nucleation. However, for some systems there is no dependence of a on W values a equal 1 up to the high values of W. Formally, this case corresponds to 8 = 0 in Eq 5.10 as a result of weak interfacial interactions.

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