Contact Angle polarization

Jute fibre treatment Water/arr contact angle Polar surface energy (mJ m ) Flexural strength of polyester composites (MPa)... 

The lENs (interpenetrating elastomer networks) are blends of two kinds of latexes, both of which are pre-cross-linked. The surface modification grafts involve grafting of polymer 2 onto the surface of a polymer 1, often to alter the surface characteristics of the material such as contact angle, polarity, or bondability. 

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. X-9. Zisman plots of the contact angles of various homologous series on Teflon O, RX , alkylbenzenes (f), n-alkanes , dialkyl ethers , siloxanes A, miscellaneous polar liquids. (Data from Ref. 78.)...

Why do you think the Cassie equation Eq. X-27 might work better than Eq. X-28 for predicting the contact angle as a function of surface polarity ... 

Most LB-forming amphiphiles have hydrophobic tails, leaving a very hydrophobic surface. In order to introduce polarity to the final surface, one needs to incorporate bipolar components that would not normally form LB films on their own. Berg and co-workers have partly surmounted this problem with two- and three-component mixtures of fatty acids, amines, and bipolar alcohols [175, 176]. Interestingly, the type of deposition depends on the contact angle of the substrate, and, thus, when relatively polar monolayers are formed, they are deposited as Z-type multilayers. Phase-separated LB films of hydrocarbon-fluorocarbon mixtures provide selective adsorption sites for macromolecules, due to the formation of a step site at the domain boundary [177]. 

The first term on the right is the common inverse cube law, the second is taken to be the empirically more important form for moderate film thickness (and also conforms to the polarization model, Section XVII-7C), and the last term allows for structural perturbation in the adsorbed film relative to bulk liquid adsorbate. In effect, the vapor pressure of a thin multilayer film is taken to be P and to relax toward P as the film thickens. The equation has been useful in relating adsorption isotherms to contact angle behavior (see Section X-7). Roy and Halsey [73] have used a similar equation earlier, Halsey [74] allowed for surface heterogeneity by assuming a distribution of Uq values in Eq. XVII-79. Dubinin s equation (Eq. XVII-75) has been mentioned another variant has been used by Bonnetain and co-workers [7S]. 

The polarization model suggests strongly that orientational effects should be present in multilayers. As seen in Section X-6, such perturbations are essential to the explanation of contact angle phenomena. 

Detergents may be produced by the chemical reaction of fats and fatty acids with polar materials such as sulfuric or phosphoric acid or ethylene oxide. Detergents emulsify oil and grease because of their abiUty to reduce the surface tension and contact angle of water as well as the interfacial tension between water and oil. Recent trends in detergents have been to lower phosphate content to prevent eutrification of lakes when detergents are disposed of in municipal waste. 

To inspect for contaminants, a water break test is frequently employed. Water, being a polar molecule, will wet a high-energy surface (contact angle near 180 ), such as a clean metal oxide, but will bead-up on a low-energy surface characteristic of most organic materials. If the water flows uniformly over the entire surface, the surface can be assumed to clean, but if it beads-up or does not wet an area, that area probably has an organic contaminant that will require the part be re-processed. 

Measurement of the contact angle at a solid-liquid interface is a widely used method for the determination of the surface energy of solid polymers. Fowkes [1] first proposed that the surface energy of a pure phase, y y could be represented by the sum of the contribution from different types of force components, especially the dispersion and the polar components, such that ... 

The effect of irradiation of samples in the absence of TAC on the contact angles is also reported in Table 7. Modification of the surface takes place, as is evident from the decrease in the contact angles of water and formamide. The change, which is maximum at an irradiation dose of 10 Mrad, is due to the generation of polar functionalities on the surface. This is also corroborated from the IR/XPS studies described later. The contact angles are lowered further when TAC is incorporated in the system (compare TO/5 with Tl/5, TO/15 with Tl/15, etc.)... 

The change in surface wettability (measured by the contact angle) with concentration for the three surfactants is plotted in Fig. 2.54 (Zhang and Manglik 2005). The contact angle reaches a lower plateau around the CMC where bilayers start to form on the surface. Wettability of non-ionic surfactants in aqueous solutions shows that the contact angle data attains a constant value much below CMC. Direct interactions of their polar chain are generally weak in non-ionics, and it is possible for them to build and rebuild adsorption layers below CMC. The reduced contact an-... 

The treatment with sulfuric acid produces a noticeable decrease in contact angle (i.e., improved wettability) due to the removal of zinc stearate and the formation of polar moieties on the mbber, mainly the creation of highly conjugated C=C bonds and the sulfonation of the butadiene units (Figure 27.1), i.e., the hydrogen of C—H bond is removed and replaced by a SO3 molecule, which is then hydrogenated to form a sulfonic acid at the site of attachment. The treatment is not restricted to the surface but also produces a bulk modification of the mbber. 

The decrease in the contact angle and corresponding increase in the work adhesion of the modified surfaces are due to the generation of polar carbonyl (C=0) and ether (C=0=C) groups on the surfaces formed through interaction of macroradicals on EPDM backbone with atmospheric oxygen. The results have been confirmed from IR (Figure 31.4) and X-ray photoelectron spectroscopic (XPS) observation (Table 31.5). 

The next two chapters are concerned with wetting and capillarity. Wetting phenomena are still poorly understood contact angles, for example, are simply an empirical parameter to quantify wettability. Chapter 6 reviews the use of scanning polarization force... 

The presence of the polar hydrogel on the surface of PET films led, as seen from Table V, to a decrease in their contact angle with water and to a corresponding rise of the critical surface tension through the polar component... 

The contact angle with formamide remained almost the same. As shown in Figure 5, the contact angle with water further decreased in time since the absorption of water by pHEMA incorporated in PET is accompanied by swelling of the hydrogel, thereby increasing the surface polarity and ability of the film to be wetted. 

---