Polymers, contact angles wettability

Surface composition and morphology of copolymeric systems and blends are usually studied by contact angle (wettability) and surface tension measurements and more recently by x-ray photoelectron spectroscopy (XPS or ESCA). Other techniques that are also used include surface sensitive FT-IR (e.g., Attenuated Total Reflectance, ATR, and Diffuse Reflectance, DR) and EDAX. Due to the nature of each of these techniques, they provide information on varying surface thicknesses, ranging from 5 to 50 A (contact angle and ESCA) to 20,000-30,000 A (ATR-IR and EDAX). Therefore, they can be used together to complement each other in studying the depth profiles of polymer surfaces. 

Feast WJ, Munro HS and Richards RW (Eds), "Polymer Surfaces and Interfaces II", Wiley, Chichester, 1993. Fowkes FM, In "Contact Angle, Wettability and Adhesion", Adv Chem Ser 43, Am Chem Soc 1964, p. 108. 

S. S. Voyutskii, Autohesion and Adhesion of High Polymers, Interscience, New York, 1963. —, Contact angle, wettability and adhesion, Adv. Chem. Ser. 43, Am. Chem. Soc.,... 

Fort, T., Jr., The wettability of a homologous series of nylon polymers, in Contact Angle, Wettability, and Adhesion, Advances in Chemistry Series, vol. 43, American Chemical Society, Washington, D.C., 1965, p. 302. 

Grundke, K. Nitschke, M. Minko, S. Stamm, M. Froeck, C. Simon, F. Uhlmann, S. Poschel, K. Motornov, M. Merging Two Concepts Ultrahydrophobic Polymer Surfaces and Switchable Wettability. In Contact Angle, Wettability and Adhesion Mittal, K. L., Ed. VSP Utrecht, The Netherlands, 2003 Vol. 3, 267-291. 

McDonald R (ed) (1997) Colour physics for industry, 2nd edn. Society of Dyers and Colourists. West Yorkshire, England Meeten GH (1986) Optical properties of polymers. Springer, New York Miller ML (1966) The structure of polymers. Reinhold, New York Mittal KL (2003) Contact angle, wettability and adhesion, vols 1—3. VPS International Science Publishers, Zeist, The Netherlands Mittal KL (ed) (2004) Silanes and other coupling agents, vol 3. VSP International Science, New York... 

The most obvious change in an oxidation of the PP surface results in an increase in the wettability of the polymer. The PP shows a great decrease in contact angle with water or water/alcohol (3 1) after treatment with ozone or ozone-UV irradiation or atomic oxygen (Table 1). 

The surface properties as studied by contact angle measurement are not affected much by the composition of reacting solution so far the solvent is the same. Wettability of all samples plotted in Figures 2 and 3 depends merely on the total amount of graft polymer and the contact angle - IR absorbance plots fall on the same line as shown in Figure 7. 

The wettability of ABS can be increased by the treatment with an atmospheric plasma torch (64).. This was established by contact angle measurements and other methods. The wettability was increased when the atmospheric plasma treatment was done in a slow manner. The decrease in contact angle with respect to water is explained due to a significant increase in the oxygen content, which is caused by the formation of carboxylic and hydroxyl groups on the polymer surface. 

The modification of the chemical composition of polymer surfaces, and thus their wettability with chemical substances, can be realized in different ways electric discharges more commonly called Corona effect, oxidation by a flame, plasma treatment, UV irradiation and also UV irradiation under ozone atmosphere. Numerous studies have been devoted to the effects of these different treatments. More recently, Strobel et al. [204] compared the effects of these treatments on polypropylene and polyethylene terephthalate using analytical methods such as E.S.C.A., F.T.I.R., and contact angle measurements. They demonstrated that a flame oxidizes polymers only superficially (2-3 nm) whereas treatment realized by plasma effect or Corona effect permits one to work deeply in the polymer (10 nm). The combination of UV irradiation with ozone flux modifies the chemical composition of the polymers to a depth much greater than 10 nm, introducing oxygenated functions into the core of the polymer. 

The wettability of a polymer film normally is determined by static contact angle measurements. The surface free energy (SE) of a polymer can be determined by wettability measurements with two different liquids. The dispersion force and polar contributions to SE, 7 d and 7 p respectively, are also calculated normally by using the Owens and Wendt, and Kaelble methods [146,147], The measurements of contact angles (CA) on a given solid surface is one of the most practical ways to obtain surface free energies. 

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. 

Contact angles for a variety of liquids on pure amorphous polymer surfaces have been reported by Zisman and co-workers (12, 13). They have also shown (8) that the diffusion of low-molecular weight compounds from within a solid polymer film to its surface results in adsorption and a subsequent change in the wettability of that surface by specific liquids. In a few instances (9, 10), contact angle measurements have been used to show that surface changes in polymers are induced by ionizing radiation. 

An empirical relationship has been shown between the contact angles for wettability of a polymer film and the degree to which photooxidation products have accumulated in the surface layers of the film. Changes in wettability of polymer films during photooxidation are markedly dependent on the nature of the polymer. In the detection and identification of the earliest processes and products of surface photooxidation, the wettability method is far more sensitive than the infrared transmission or attenuated reflectance spectra and is about as sensitive but more specific than the ultraviolet transmission spectrum. Contact angle measurements themselves can be used as leads in the selection of solvents for the separation and identification of photooxidation products formed in the surface layers of a polymer film and are potentially useful in establishment of rates of specific processes. 

The surface wettability by water drops has been clearly linked with the concentration of chemically bound nitrogen in the surface. Conversely, measurements of advancing and receding contact angles for water can provide information regarding surface composition. On the other hand, there appears to be little or no direct correlation between water wettability and adhesive strength of evaporated aluminum films. Substantial improvement in adhesion of Ai to many polymers can be achieved by 02 plasma treatment of the polymer surface before metallization. Other workers have shown this to result in chemical linkages between the metal and polymer surface moieties. 

The wetting of a polymer surface is characterized by the interfacial tension between the liquid and the surface. The contact angle at the three-phase line is a good measure of the wettability of the surface. Figure 25.5 depicts the force balance... 

Figure 26.8 The effects of plasma polymerization coatings on the wettability of conventional polymers given by the cosine of the static advancing contact angle, 0s each value of the static contact angle was taken for the largest droplet size attained during the advancing process whereby the droplet size dependence is small, dotted lines indicate the mean cos 0s of the TMS and (TMS + O2) treated polymers.

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