INTERFACIAL-TENSION IN POLYMER BLENDS .1. THEORY

In this first part, the theoretical models were evaluated for their su itability to calculate the interfacial tension coefficient, v(12). Two types of theoretical treatment have been examined, the lattice theori es, and the semi-empirical correlations based on the surface tension c oefficient of the blend components. There is a diversity of the lattic e model expressions based on different sets of assumptions. These rela tions are expected to be valid within a specified range of conditions that in practice are difficult to foresee. Furthermore, owing to diffi culties in determining the values of equation parameters, e.g., the la ttice parameters, and the binary interaction function chi(12)=f(T' phi ), they are complicated to use. When the experimental values of the su rface tension coefficients are known, the harmonic-mean method provide s good correlation. A new, square-root difference equation was propose d that also provides satisfactory approximation. Validity of the relat ions was examined using literature data for 20 polymer blends. More fu ndamental, new equations for calculating the interfacial tension coeff icient from the solubility parameter were derived. The new dependencie s make it possible to compute the interfacial tension coefficient from the structural units of the macromolecules, at any temperature. Valid ity of these relations was evaluated using the literature data for 46 blends.