Wettability polymer surfaces

Poljraer surfaces can be easily modified with microwave or radio-frequency-energized glow discharge techniques. The polymer surface cross-links or oxidizes, depending on the nature of the plasma atmosphere. Oxidizing (oxygen) and nonoxidizing (helium) plasmas can have a wide variety of effects on polymer surface wettability characteristics (92). 

The corona-treated PE surfaces were used to study the effect of polymer surface wettability on cell adhesion and growth. Chinese hamster ovary (CHO) cells (CHO-KI-BH4, Oak Ridge National Laboratory, USA) were used as a model system because they exist as reasonably stable single cells and are not unreasonably fastidious in terms of culture requirements (21). They are grown in monolayer with fast generation time (about 12 hr). 

UV irradiation on a polymer surface produces chemical modification as well as wettability and bondability improvement. It causes chain scission and oxidation on polymer surfaces. -iven in the presence of an inert gas [45]. Carbonyls are found to be introduced onto polyethylenes on UV irradiation. Sivram et al. [46] have used photochemical treatments for surface modification of polymers. They have generated surfaces of vaying surface energies by simple organic reactions. 

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. 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

The common polymers are composed of a small number of elements whose XP spectra are simple (generally C Is plus one or two peaks from Ols, Nls, FIs and Cl 2s, 2p). Common contaminants contain additional elements such as S, P, Si, A1 and heavy metals, and the presence of these elements, even in low concentrations, can be detected very easily. Polymer surface modification is an area in which XPS has been fruitfully applied, notably in the study of commercial pretreatments aimed at improving wettability and general adhesion characteristics. 

Lee JH, Khang G, Lee JW, Lee HB (1998) Interaction of different types of cells on polymer surfaces with wettability gradient. J Colloid Interface Sci 205 323-330... 

The prototype of the present surface photografting is the surface photoreaction of maleic anhydride(MAH) onto poly(butadiene) film(15). Although fair improvement of surface wettability was achieved, photoaddition of MAH cannot be applied to other polymers having no ethylenic double bonds. The present process is applicable to almost all polymers except for poly(tetrafluoroethy-lene) and its analogues. 

The total swelling time for a dried SPH in aqueous solution is determined by two factors q and t2- h is the time for water to reach all the surface of the pores in the SPHs. It is determined by the effectiveness of the capillary action in a SPH. 2 is the actual swelling time of the polymer matrix, which is determined by the thickness of the cell walls and struts. Because the cell walls and stints of SPHs are very thin, they have very short characteristic swelling times. For SPHs, t2 is comparable to that of a ultrathin hydrogel film. The capillary action is mainly determined by the availability of capillary channels and the wettability of the channels. Various approaches have been attempted to maintain good capillary action (i.e., to decrease q) by maintaining open intercellular channels and good surface wettability. 

During the plasma surface reaction, the plasma and the solid are in physical contact, but electrically isolated. Surfaces in contact with the plasma are bombarded by free radicals, electrons, ions, and photons, as generated by the reactions listed above. The energy transferred to the solid is dissipated within the solid by a variety of chemical and physical processes, as illustrated in Figure 7.95. These processes can change surface wettability (cf. Sections 1.4.6 and 2.2.2.3), alter molecular weight of polymer surfaces or create reactive sites on polymers. These effects are summarized in Table 7.21. 

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. 

Elemental sodium, as well as other alkali metals, reacts with perfluorocarbon polymers by removing fluorine from them. This reaction has a practical application for improving surface wettability and adhesive bonding of perfluorocarbon polymers to other substrates.57... 

Several techniques including corona discharge [1], plasma treatment [1,3,4], flame treatment [1], and irradiation with UV light in the presence of a UV sensitive gas [5-8] have been developed to modify the polymer surface. The principle of those surface treatment technologies is to introduce polar groups onto the polymer surface. This provides significant improvement of wettability, paintability, biocompatibility and also adhesion to other polymers or metals. 

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. 

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. 

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