Polymers, surface free energy data

At high crystallisation temperatures, the high molar mass polymer crystallised alone. Data for the fold surface free energy obtained from linear growth rate data supported the view that the nature of the fold surface of the dominant lamellae was related only to the molar mass of the crystallising component and was not affected by the composition of the melt. 

The Cahn approach describing simple fluid mixtures has been adopted by a mean field theory developed for polymer mixtures by Nakanishi and Pincus [61] and Schmidt and Binder [15] and is presented in the next section. The mean field theory and its various extensions [7] have been successfully used to describe much of the experimental segregation isotherm z (())<, ) data obtained so far [16, 92,120,145,165-167,169-175]. It allows us not only to distinguish isotherms z (J characteristic for partial and complete (first and second order) wetting but also to determine surface free energy parameters useful in predicting surface phase diagrams for the studied mixtures. 

Inverse gas chromatographic measurements may be carried out both at infinite dilution and at finite solute concentrations [1]. In the first case vapours of testing solutes are injected onto the colurtm and their concentrations in the adsorbed layer proceed to zero. Testing substances interact with strong active sites on the examined surface. The retention data are then converted into, e.g. dispersive component of the surface free energy and specific component of free energy of adsorption. In the second case, i.e. at finite solute concentrations, the appropriate adsorption isotherms are used to describe the surface properties of polymer or filler. The differential isosteric heat of adsorption is also calculated under the assumption that the isotherms were obtained at small temperature intervals. 

Erbil, H.Y. and Meric, R.A. (1988). Determination of surface free energy components of polymers from contact angle data using nonlinear programming methods. Colloids and Surfaces, 33, 85-97. 

For the values of the surface energies which must be inserted in the Dupre equation, recent surface energy data for the polymers used in this study, which were determined by Erhard (21) could be used. Erhard determined experimentally the surface free energies of the polymers and computed the work of adhesion with the method of Owens and Wendt. Table II shows the data of the work of... 

Figure 11.63. The effect of treatment time on surface free energy of PVC plasticized with 10 phr of epoxidized soybean oil and 40 phr of di-(2-e1hylhexyl) phthalate and 40 phr of poly(ethylene-co-vinyl ace-tate-eo-carbon monoxide). [Data from Audic J-L Poncin-Epaillard F Reyx D Brosse J-C, J. Appl. Polym. Sci., 79, No.8, 22nd Feb.2001, p.1384-93.]...

Two methods can be used for the assessment of y and its components contact angle measurements and inverse gas chromatography (IGC) [31]. Chibowski and Perea-Carpio [32] reviewed the problems encountered when attempting to determine the surface free energy of powered solids, like silica particles, using the contact angle technique. Wu reviewed the different techniques that can be employed to measure the surface tension of polymer melts [30]. These techniques are based on the pendant and sessile drop techniques that require density data or contact angle measurements. 

Table 59.3 is based primarily on the Zisman critical surface tension of wetting and Owens and Wendt approaches because most of the polymer data available is in these forms. The inadequacies of equations such as Eq. (59.7) have been known for a decade, and newer, more refined approaches are becoming established, notably these of van Oss and coworkers [24]. A more limited number of polymers have been examined in this way and the data (at 20 °C) are summarized in Table 59.4. is the component of surface free energy due to the Lifshitz-van der Waals (LW) interactions that includes the London (dispersion, y ), Debye (induction), and Keesom (dipolar) forces. These are the forces that can correctly be treated by a simple geometric mean relationship such as Eq. (59.6). y is the component of surface free energy due to Lewis acid-base (AB) polar interactions. As with y and yP the sum of y and y is the total solid surface free energy, y is obtained from... 

Miyata and Yamaoka [26] used scanning probe microscopy (SPM) to determine the micro-scale friction force of a silicone-treated polymer film surface. PU acrylates cured by an electron beam were used as the polymer films. The micro-scale friction force obtained by SPM was compared with macro-scale data, such as surface free energy determined by the Owens-Wendt method and the macro-scale friction coefficient determined by the ASTM D1894 method [27]. These comparisons showed that a good linear relationship existed between the surface free energy and the friction force, which was insensitive to the nature of the polymer specimens or to the silicone... 

The pull-off forces obtained in f-d measurements can be related to the work of adhesion and the respective surface free energies utilizing, eg, (continuum) contact mechanics theories, such as the Johnson-Kendall-Roberts (JKR) theory (80). In particular for monomolecular model systems (65), but also polymers, this approach has yielded a satisfactory description of the experimental data, despite the fact that the contacting bodies are treated as purely elastic (81). 

If we set out to unravel surface chemical functionalities with high spatial resolution down to atomic detail, we also encounter various practical (technical) problems. It is fair to say that the technique development for direct space analysis (again, we exclude Fourier space methods) is still lagging much behind. Chemical force microscopy can be considered as a first step in the direction of a true description of surface chemical functionalities with high spatial resolution in polymers, primarily based on the chemically sensitive analysis of AFM data via adhesion mapping. At this point the detailed theory for force spectroscopy is not developed beyond the description of London forces. The consideration of the effect of polar functional groups in force spectroscopy (similar to difficulties with solubihty parameter and surface tension approaches for polar forces, as well as specific interactions) is still in its infancy. Instead, one must still rely on continuiun contact mechanics to couple measured forces and surface free energies. 

Figure 20 summarizes the result of BSA adsorption to the polymer films. We used BSA as model for protein because albumin is the protein that is most prominently present in human blood serum. The BSA adsorption onto regenerated cellulose, which had a highly hydrophilic surface, was extremely low. These data gave the same result reported in the previous study [70]. On the other hand, the adsorbed amounts of BSA onto aramid and nylon were high (0.5-0.6 p,g/cm ). For the PASs, the amount of BSA was almost half the amounts of those with aramid and nylon, but similar to that for SILASTIC 500-1, and more than that of the regenerated cellulose. There was no difference in the adsorbed amounts onto the three samples of PASs. In the previous work, PDMS blocks were condensed at the outermost surface of PAS [10]. The phenomenon of protein adsorption onto PAS seems to be due to the low surface free-energy of the PAS surface [71-73] caused by the condensation of PDMS blocks on the outermost surface of PAS. Therefore, the BSA was bound onto PAS surface as well as the surface of the silicone rubber [74,75]. 

Attempts to correlate the adsorption data of other surfactants such as Alipal EP-110 and NaLS on the three latex surfaces in a similar manner failed because of the more complex and specific interactions observed in these systems. Equation 2 can adequately describe the adsorption data of surfactants at polymer/ water interfaces, provided that the free energy of the interface is related to the free energy of adsorption and there are no specific interactions between surfactant and interface (15). 

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