Interfacial tension between polymers experimental values

Fig. 10. (a) Interfacial tension between polymer-rich phase and solvent-rich phase as a function of pressure p at temperature kgT/e = 0.75 which corresponds to T = 314A . For p < jOtripie = 0.193174 F/cr the polymer-rich phase coexists with a solvent-vapor, while beyond the triple pressure it coexists with a solvent-rich liquid. The jump of the interfacial tension at the triple point is hardly visible on the scale of the figure. The insets show the logarithmic divergence of the interfacial excess as one approaches the triple pressure from below and the experimental values of the interfacial tension at T = 40 C= 313.15K. (b) Density profiles between coexisting phases at various pressures as indicated in the keys. From [164]... 

Theories of the interfacial tension were reviewed by Wu [1], who also provided an extensive tabulation of experimental values for amorphous polymer-polymer interfaces [2], including both homopolymers and copolymers, at several temperatures. For example, the interfacial tensions between a number of pairs of homopolymers [2] are listed in Table 7.3. 

Although knowledge of the interfacial tension in polymer/polymer systems can provide important information on the interfacial stmcture between polymers and, thus, can help the understanding of polymer compatibility and adhesion, reliable measurements of surface and interfacial tension were not reported until 1965 for surface tension [135,138] and 1969 for interfacial tension [127,154] because of the experimental difficulties involved due to the high polymer viscosities. Chappelar [145] obtained some preliminary values of the interfacial tension between molten polymer pairs using a thread breakup technique. The systems examined included nylon with polystyrene, nylon with polyethylene (PE), and poly(ethylene tere-phthalate) with PE the values are probably only qualitatively significant [174]. 

Sigillo et al. (1997) used several experimental methods for the measurement of interfacial tension of a model polymer blend. Common to all methods presented here are two main points. The first is that a is obtained from experiments where the shape of the interface between the liquids is directly observed by means of optical microscopy techniques. The second point is that the interface geometry is controlled by a balance between the interfacial force and the viscous stresses generated by some flow applied to the system. Measurements have been carried out on a model polymer blend, whose constituents are a polyisobutylene and a polydimethylsiloxane, both transparent and liquid at room temperature. When compared with each other, the values of interfacial tension obtained from the different methods show a good quantitative agreement. Excellent agreement is also found with results for the same system previously published in the literature. 

It has been demonstrated experimentally by Taylor [6,7] that for values of p from 0.1 to 1, droplet breakup occurred at D values between 0.5 and 0.6. The expression of E in Equation 1.2 indicates that the viscosity ratio, the shear stress, the droplet diameter, and the interfacial tension are critical variables to consider in controlling particle deformation and breakup in Newtonian fluids. In that equation, however, the coalescence, which has been later found to be critical in a breakup process, has not been considered. Figure 1.1 shows a nice illustration of the process of breakup of a polymer fiber (polyamide) in a polymer matrix (polystyrene). 

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