Wetting polar surfaces

Polyester diols are often combined with polyether diols to provide green strength through crystallization or elevated r . Most prevalent and least expensive is hexamethylene diol adipate (HDA) with a Tm of about 60°C. A variety of polyesters are available with various levels of crystallinity — from wax-like to amorphous — and crystallization rate, and with values ranging well below 0°C to above room temperature. Polybutadiene diols are the most expensive and most hydrophobic. They provide low surface tension and thus good wet out of non-polar surfaces. 

In printing, a film of ink is formed by wetting the surface with the compression force of the rollers. This force spreads the ink over the surface and into any capillaries that may be present. Spreading and penetration are controlled thermodynamically and kinetically. Measurement of the contact angle can be used to determine the thermodynamics of wetting. This angle can be used also to determine the contribution that polarity and dispersive forces of the liquid make to the wetting of the surface. 

In a previous paper,22 we investigated the breakthrough dynamics of tert-butylbenzene (TBB) using different activated carbons in dry and wetted beds, and dry and wet airstream. It was shown that the availability of a developed network of mesopores (and macropores as transport pores), a low nonuniformity of pores and surfaces, and a low affinity with respect to water (low content of polar surface sites), are necessary conditions for a high effectiveness of carbon adsorbents in the adsorption of organics characterized by an extension of the critical breakthrough time. 

Hong et al. examined the effect of nitric acid passivation on type 430 ferritic stainless steel using potentiodynamic polarization, EIS, and Auger electron spectroscopy (AES) (18). Passivation treatments were carried out on wet polished surfaces by immersion for 60 minutes in nitric acid solutions ranging from 1 to 61% at 50°C. Pitting potential and the magnitude of the total impedance were positively correlated with surface Cr concentration. In response to this study,... 

Surface and transport properties of solvents are very important for solvents. Surface tension of a solvent shows how easy or difficult it would be to wet the surface on which the solvent is being applied. Low surface tension implies better wetting ability and vice versa. Water and other polar organic solvents have very high surface tension, whereas silicones, fluorocarbons, and aliphatic hydrocarbons have low surface tension. Solvents with low surface tension are easier to leak through threaded joints compared to those with high surface tension. 

The work of adhesion (see Chapter 1,1) reflects the degree to which unsaturated molecular interactions between solids and liquids in contact are balanced. The value of cos 9, which is symbatic to the work of adhesion, is also a measure of the degree of similarity between the solid surface and a liquid (liophilicity). Polar surfaces that are wetted by water well are hydrophilic, while those poorly wetted (solid hydrocarbons, and particularly fluororinated polymers) are hydrophobic. Since the value of 0 is determined by both the work of adhesion and the work of cohesion, a comparison of the contact angles formed by different liquids at the same solid surface does not allow one to compare the works of adhesion (the degree of similarity in the nature of the liquid and solid) directly. For example, polar surfaces are equally wetted well by both water and hydrocarbons. 

Under these conditions the value of ocr is close to that of the surface energy of the solid, i.e., ocr ctm. The value of oSG can be obtained by measuring the contact angle, 9, for several nonpolar liquids and extrapolating linear cos 9 = /( aLG l/2) to cos 9=1. For instance, for polyethylene oSG = 31 mJ/m2. If a non-polar surface for which the surface energy was determined in this way is wetted with a polar liquid of known surface tension (e.g. water), one can obtain the dispersion component of the surface tension of the polar liquid, odLG, from... 

Fig. 3.12. Edge wetting angle of pentaplast coatings by glycerin as a function of the coating s polarization surface charge...

High hydrophilicity of HDS is due to the presence of a hydroxylic cover and electron-accepting silicon atoms of silanol groups. The surface of HDS is able to sorb polar molecules. Water wets the surface of HDS well, which leads to formation of thin slurries (suspensions) or gels of various consistencies depending on the ingredient ratio. 

Ethyl cyanoacrylate is a little less polar than methyl cyanoacrylate, and has the ability to wet plastic surfaces more readily, and is a better solvent for plastics. With this added ability to make intimate contact with the surface, the bonds on plastic are stronger with ethyl cyanoacrylate than with the methyl ester. This difference in performance gives rise to the adage that methyl is for metal and ethyl is for everything else. Sometimes this difference can be utilized in reverse to good advantage to avoid stress cracking on such sensitive plastics as polycarbonate and polyacrylate. 

The equilibrium wetting behavior of simple liquids (including low MW polymers) on low polarity polymer surfaces is well documented and consistent with Gibbsian thermodynamics within specific constraints. Empirical relationships have been established between observed contact angles and polymer surface chemical composition. Predictive relationships have been established between contact angles and polymer substrate surface chemistry based on the theory of fractional polarity surface energies can be factored into dispersion and polar components. These relationships seriously break down with increasing polarity of either the liquid or solid surface. 

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