Surface tension of polymers

The surface tension of polymers (synthetic polymers such as plastics, biopolymers such as proteins and gelatin) is indeed of much interest in many areas. In industry where plastics are used, the adhesion of these materials to other materials (such as steel, glass) is of much interest. The adhesion process is very complex since the demand on quality and control is very high. This is also because adhesion systems are part of many life-sustaining processes (such as implants, etc.). The forces involved in adhesion need to be examined, and we will consider some typical examples in the following text. 

Table 3.4 Critical surface tension of polymer solids [10] ...

Table 8.2 compares the experimental values of the surface tension of polymers (obtained by different methods) and the calculated values, the latter being obtained by means of the parachor. The discrepancies between the different experimental values are reasonably small. The calculated values are, with a few exceptions, in reasonable agreement with the experimental values. 

TABLE 8.2 Experimental0 and calculated values of surface tension of polymers expressed in mj/m2 = mN/m... 

The analysis of variance and the method of regular regression are used in evaluating the results. Equation improvements are discussed. The difficulties in predicting surface tensions of polymers on the basis of bulk properties are emphasized. 

Tn recent years, developing interests in surface energetics and adhesion of liquid-like polymers, or polymer liquids, have prompted both theoretical and experimental work on surface tension. Unlike low molecular weight liquids, polymer liquids have not been extensively studied. Bondi and Simkin (1) mentioned surface tension in their study on high molecular weight liquids. Roe (28) applied both the cell theory of polymer liquids and the hole theory of surface tension of simple liquids to develop an approximate theory of surface tensions of polymer liquids. His approach has met some degree of success. Notably, both Bondi s and Roes work are somewhat related to the cell theory introduced by Prigogine and... 

The direct measurement of surface tensions of polymer melts (10, 27, 29, 30, 37) generally yields values somewhat greater than those obtained indirectly, depending on the method and the instrument. Unfortunately, structure correlation studies cannot be undertaken until more direct surface tension data have been obtained. 

Figure 2. Comparison of the observed and the calculated critical surface tensions of polymers (on the basis of solubility parameter)...

This method has been applied successfully in the determination of the surface tensions of polymer particles (140,141,1591, coal particles (160,161). and biological cells [162-168], Contact angles predicted from these surface tensions involving solids agree well with experimental contact angles f 159]. 

Surface dynamics is concerned with the kinetic aspect of this specific question of whether or not the surface tension of polymer changes by contacting with liquid water. If ys changes by the interaction of water with polymer molecules, Ysl also changes accordingly. 

The interfacial tension may be dealt by the differential surface tension, A(ys), (the difference between surface tension of polymer and that of contacting phase) ... 

This ratio is transformed to Fowkes equation when the polar term is negligibly small. Using Eq. (4) and experimental data on interfadal and surface tension of polymers, Wu calculated the polarity of some polymers. He estimates the contribution of the polarity to the surface tension of polymers to be considerable. Thus, for polylvinyl acetate) it takes up 33%, for poly (methyl methacrylate) 28%, and for polychloroprene 11%. 

The lattice fluid equation-of-state theory for polymers, polymer solutions, and polymer mixtures is a useful tool which can provide information on equa-tion-of-state properties, and also allows prediction of surface tension of polymers, phase stability of polymer blends, etc. [17-20]. The theory uses empty lattice sites to account for free volume, and therefore one may treat volume changes upon mixing, which are not possible in the Flory-Huggins theory. As a result, lower critical solution temperature (LCST) behaviors can, in principle, be described in polymer systems which interact chiefly through dispersion forces [17]. The equation-of-state theory involves characteristic parameters, p, v, and T, which have to be determined from experimental data. The least-squares fitting of density data as a function of temperature and pressure yields a set of parameters which best represent the data over the temperature and pressure ranges considered [21]. The method,however,requires tedious experiments to deter-... 

Extrapolation of the surface tension data for polymer melts to room temperature. This is often considered to be the most reliable method for estimating the y of a solid polymer. See Table 7.1 for surface tensions of polymers [2] measured by using this method. 

Table 7.2. Combined polar and hydrogen bonding components (yx) of the surface tensions of polymers, in dyn/cm [1,3,10]. Note that the differences are usually large when more than one yx value has been reported for a given polymer, underscoring the difficulty of making accurate and reproducible determinations of this quantity. 

Erbil, H.Y. (1997). Surface Tension of Polymers. In Birdi, K.S. (ed.). Handbook of Surface and Colloid Chemistry. CRC Press, Boca Raton. 

PVT data for polymers are important both from the academic and practical points of view. On the scientific side, PVT data are frequently needed for model considerations on polymer solutions and melts. On the industrial side, these data are needed for process design. An equally important thermodynamic quantity is the surface tension of polymer melts, due to their relevance in wetting, adsorption, and adhesion. It may strongly govern such surface processes as film formation or coating. Here we report on PVT data and surface tensions of different random copolymers. We also relate thermodynamic quantities describing bulk properties to surface tension of polymer melts. 

Kwok, D. Y., Cheung, L. K., Park, C. B., and Neumann, A. W., Study on the surface tensions of polymer melts using axisymmetric drop shape analysis, Polym. Eng. Sci., 38, 757-764 (1998). 

The slope constant Ke is influenced by the chemical nature of the end groups, as shown in Figure 12-2. 7 is independent of the molar mass and the nature of the end groups. Typical surface tensions of polymer liquids of finite molar mass are given in Table 12-1. The surface tensions do notvary very much with temperature. 

The critical surface tension of all known solid polymers is lower than the surface tension of water at 72 X 10 N/cm (Table 12-2). All polymers are therefore relatively poorly wetted by water. The critical surface tension of polymers containing fluorine is particularly low, and they are poorly wetted... 

The wetting behavior of polymers is reviewed beginning with the thermodynamic conditions for contact angle equilibrium. The critical surface tension of polymers is discussed followed by some of the current theories of wettability, notably the theory of fractional polarity and theories of contact angle hysteresis. The nonequilibrium spontaneous and forced spreading of polymer liquids is reviewed from two points of view, the surface chemical perspective and the hydrodynamic perspective. There is a wide di.sperity between these two viewpoints that needs to be resolved inorder to establish the predictive relations that govern spreading behavior. 

The primary peculiarity of the system under consideration is the fact that increase of the quantity of surfactant does not always result in decrease of surface tension. Thus, the surface tension of polymer containing 1% of L-19 is higher than that of a polymer containing 0.05% or 0.5% of L-19. Additionally, increase of the surfactant content of the liquid oligomer always results in the decrease of the surface tension (naturally when the surfactant concentration in the system is lower than CCMF). 

HOLE THEORY OF SURFACE TENSION OF POLYMER LIQUIDS. 

SURFACE TENSIONS OF POLYMER LIQUIDS BY A ROTATING BUBBLE METHOD. M.S. THESIS, CHEMISTRY. 

CALCULATION OF CRITICAL SURFACE TENSIONS OF POLYMERS AND SURFACE TENSIONS OF LIQUIDS FROM CHEMICAL STRUCTURE ONLY. 

The surface chemistry of the substrate, even if the substrate is homogeneous, will affect the film phase segregation (see Fig. 6.2). In a two component blend film of two polymers—let us call them polymer A and polymer B— if the surface tension of polymer A and the substrate is less than the surface tension of polymer B and the substrate, polymer A will tend to sink towards the substrate and polymer B will tend to rise from the substrate, producing a vertically phase segregated film. Substrate interactions tend to dominate the atmospheric interactions, though a similar process can lead to vertical phase separation at the atmospheric interface. 

SURFACE TENSION OF POLYMER BLENDS AND RANDOM COPOLYMERS... 

The surface properties of polymers are important in technology of plastics, coatings, textiles, films, and adhesives through their role in processes of wetting, adsorption, and adhesion. We will discuss only surface tensions of polymer melts that can be measured directly by reversible deformation or can be inferred from drop shapes. Those inferred from contact angles of liquids on solid polymers ( critical surface tension of wetting ) are excluded, as their relations to surface tensions are uncertain. 

Most of the polymers are veiy viscous even at high temperatures. Moreover, they exhibit non-Newtonian flowing behavior. Considerable care is required to ensure precise measurements. We will discuss here surface tensions of polymer blends and of random copolymers especially, we will focus on its variation with composition. 

Surface Tension of Polymer Blends and Random Copolymers... 

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