Surface energy and contact angle

Surface tension, surface energy, and contact angle 353... 

Finally, the components of PPA-1 and PPA-2 are optimized to prevent their migration from within solidified polyethylene. It is only in the melt phase under shear that the PPAs are allowed to function. To confirm this, the same films that were extruded for mechanical property measurements were evaluated over a year-long period for any surface changes. Surface energy and contact angle measurements, along with ESCA (Electron Spectroscopy for Chemical Analysis) and SSEMS (Static Secondary Ion Mass Spectroscopy) verified that there was no physical or chemical presence of intentionally elevated PPA levels. 

PSAs must meet the same criteria as other adhesives with regard to surface energy and contact angle so that they have a driving force to spread on the substrate. However, because PSAs are not low viscosity liquids, it is difficult to measure contact angle or surface tension in the usual ways. Often we infer these properties from the behavior of chemically similar low molecular weight analogs to the PSA. 

Of particular interest in Fig. 6 are the changes in surface energy and contact-angle slope relative to those of plain Zoltek PANEX cloth (a material similar to the... 

As these other chapters show, there is a well-developed thermodynamic theory of wetting and spreading. This relates surface energies and surface tensions to contact angles and extent of wetting. Where the relevant surface energies and contact angles are known, or can be deduced, the extent of contact between a specific adhesive and substrate at equilibrium can be predicted. The essential idea of the adsorption theory of adhesion is that whenever there is contact between two materials at a molecular level, there will be adhesion. 

It should be emphasized that evaporation and condensation are very complex nonequilibrium topics that are the source of many specialized textbooks. The processes of condensation and evaporation are related to physicochemical parameters, including temperature, vapor pressure, surface tension, surface energy and contact angle, surface impurities, homogeneity and roughness. Phase change is a local phenomenon, and some degree of local supersaturation is required to initiate condensation and desublimation. 

As we see in Chapter 6, surface tension and contact angle measurements provide information on liquid-liquid and solid-liquid adhesion energies (Fig. 1.26c). Contact angles measured under different atmospheric environments or as a function of time provide valuable insights into the states of surfaces and adsorbed films and of molecular reorientation times at interfaces. 

Adsorption of bases (n-bu-tylamine) in aprotic solvents using Hammett or arylmeth-anol indicators Wetting with liquids Microscopy Total content of surface acid sites, acidity distribution Surface energy, surface wettability, and contact angle 25... 

Surface energy, surface wettability, and contact angle... 

Physical-property tests are used to measure the properties of adhesives in the liquid or gelled states prior to curing and in the solid state after curing. Tests for the uncured state such as viscosity, visual examination, and surface energy or contact angle assure that fillers, if used, have not settled out, that the material has not exceeded its pot life or shelf life, and that the supplier has not changed the formulation. Visual examination and density after cure are performed to verify that voids are not present or, if present, meet specification requirements. Finally, light transmission and index of refraction measurements are important for adhesives used in optoelectronic applications. 

It is weU known that the selective adsorption of surfactants at the solid-water interface imparts hydrophobicity to the surface of the solid. The relative hydrophobicity of the solid surface is responsible for various macroscopic properties observed experimentally. For example, in mineral separation, the hydrophobicity of the solid surface leads to selective bubble-particle attachment, which accounts for the selective flotation of minerals in large scale industrial plants. The relative measure of mineral surface hydrophobicity is usually quantified in terms of contact angle measurements and flotation experiments (Fuerstenau 1957, 1970, 2000 Fuerstenau and Herrera-Urbina 1989 Fuerstenau and Pradip 2005 Pradip 1988). Molecular-modeling tools can be successfully employed to compute the interaction energies and contact angle on both virgin and surfactant-covered mineral surfaces. The relative flotation efficacy of different surfactants can thus be related to their molecular structure and properties. 

Fuerstenau, D. W., Diao, J. and Hanson, J., Estimation of the distribution of surface sites and contact angles on coal particles from film flotation data. Energy Fuels, 4, 34-37 (1990). 

FIGURE 1.8 Reduction of critical Gibbs free energy for nucleation as functions of surface curvature and contact angle. The numbers atop the curves are the contact angle values used for the construction of the particular curve. 

---