Contact Angle Method

Yi = the surface tension of the chosen liquid Ys = the surface tension of the solid (polymer) Ysi = the liquid-solid surface tension 

Young s equation is the basis of the study of liquid-solid infiltration function, and the contact angle is often used to measure the infiltration effect of the liquid on the solid. The 

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Given the importance of surface and interfacial energies in determining the interfacial adhesion between materials, and the unreliability of the contact angle methods to predict the surface energetics of solids, it has become necessary to develop a new class of theoretical and experimental tools to measure the surface and interfacial energetics of solids. Thia new class of methods is based on the recent developments in the theories of contact mechanics, particularly the JKR theory. 

The adsorption of gas onto a solid surface can also be used to estimate surface energy. Both inverse gas chromatography (IGC) and isotherm measurement using the BET method [19] have been used. Further discussion and detailed references are given by Lucic et al. [20] who compare the application of IGC, BET and contact angle methods for characterising the surface energies of stearate-coated calcium carbonate fillers. 

All data refer to room temperature if not stated otherwise. CA = Contact angle method. See also list of symbols. 

The wetting (contact) angle method is used for solid surfaces. If a gas bubble sticks to a metal surface, then the individual interfacial tensions are distributed as shown in Fig. 4.11. It holds at equilibrium that... 

SURFACE ENERGY VS. PERCENT ETHANOL IN WATER (Contact Angle Method)... 

In this section, we have examined the characteristics of fiber surfaces obtained by two-liquid tensiometric technique which could allow the energetic study of cylindrical solids with very small diameter, comparing to the classical contact angle method. 

The effect of ultraviolet irradiation in air on the wettability of thin films of amorphous polymers has been studied. With poly(vinyl chloride), poly(methyl methacrylate), poly(n-butyl methacrylate), poly (ethylene terephthalate), and polystyrene the changes in contact angles for various liquids with irradiation time are a function of the nature of the polymer. A detailed study of polystyrene by this technique and attenuated total reflectance spectra, both of which are sensitive to changes in the surface layers, indicates that the contact angle method is one of the most sensitive tools for the study of polymer photooxidation in its early stages. The method is useful in following specific processes and in indicating solvents to be used in the separation and isolation of photooxidation products. 

Owing to the last problem the contact angle method has mainly been applied to low-energy surfaces like polymers 1112,122— 126J or silicas grafted with alkyl chains [ 127, 28. Some results are summarized in Table 9. In addition, it is often used to determine the surface tension of materials with a high specific surface area like powders or porous substances 1129-133). In that case the rise of the test liquids in a capillary filled with the substance is measured. 

Y. Tamai, T. Matsunaga and K. Horluchl, J. Colloid Interface Set 60 (1977) 112 comparison with data obtained with two-liquid contact angle method. 

Table II shows the main characteristics of some of the probes used in this work. The surface area a of the probe molecules was determined by injecting the probes onto neutral reference solids (PTFE, polyethylene, etc). The dispersive component Yl was measured by the contact angle method on reference solids ( ). The values of DN and AN were taken from tables published by Gutmann (24).

The dispersive component is associated with polymer-filler interaction and the specific component is associated with filler networking and agglomeration. The dispersive component of different fillers is more conveniently measured by inverse gas chromatography although it can also be measured by contact angle methods. The work of adhesion is given by the following equation, which has been modified to account for Fowkes theoiy. 

Dynamic contact angles are the angles which can be measured if the three-phase boundary (liquid/solid/vapor) is in actual motion. A Wilhelmy plate is used in dynamic contact angle measurements, and this method is also called the tensiometric contact angle method. It has been extensively applied to solid-liquid contact angle determinations in recent years. In practice, a solid substrate is cut as a thin rectangular plate, otherwise a solid material is... 

Many interesting correlations have been established between the critical surface tension of materials (or other approximations of surface free energy) and protein adsorption, cell adhesion, and thrombus formation (41-48). Unfortunately, very few studies in which a biological response has been related to a specific surface chemistry exist. One study in which such a relationship was established, demonstrated the power of the contact angle method in analyzing surface structure related to blood compatibility (40). The blood compatibility of Stellite alloy heart valves was not due to the alloy itself, but to the closely packed methyl group structure associated with a tallow polishing compound used to finish the valve. Very recently, the power... 

Critical surface tension jc mN m 20°C, contact angle method 52.3 (24)... 

Beginning from the fifties of the last century, the investigation of the behavior of solid electrodes came into the foreground. The available methods, for instance, wetting (contact) angle method, the measurement of differential capacity, were far from furnishing reliable data in the case of solid electrodes. 

The fallowing techniques were used to characterize chemical and morphological changes in the PET samples surface free energy conponents by the contact angle method, DTA, DSC, calorimetry, thermooptical method, IR spectroscopy, SBH, and XPS. 

The Wilhelmy plate contact angle method might provide a sequential scanning curve or hysteresis loop that can be interpreted in terms of surface mobility, reorientation, solvent penetration, and intrinsic wettability under both water and air. Water is known to be a difficult liquid for use in contact angle studies due to its small molecular volume, resulting in penetration and local swelling of the solid surfaces [15]. 

The surface tension of solid plastics cannot be measured directly and is thus determined indirectly, usually by contact angle methods. The problem with the direct measurement of surface tension arises from the difficulty in the reversible formation of a solid surface. 

Berg has provided a wide-ranging discussion of a range of methods - many described as tedious - by which acid-base interaction can be obtained. In addition to the method of Fowkes, considered above, two others are described Inverse gas chromatography and the contact angle method introduced by Good, Chaudhury and van Oss, which involves Acid-base surface energy parameters. 

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