a) b - École Polytechnique de Montréal

2.1.2.2 Ternary Polymer Blends
Mathematical models derived from physical considerations have been successfully used to
predict and explain several observed morphologies of immiscible ternary polymer blends. Harkin
used thermodynamic properties, such as surface and interfacial tensions of the components, to
express the tendency of liquid to spontaneously spread across a solid or liquid substrate(Harkins
& Feldman, 1922). The first comprehensive study on a ternary liquid mixture was carried out by
Torza and Mason(Torza & Mason, 1970). They used modified Harkins Spreading Theory to
analyze interfacial energy differences between the liquid components. Hobbs et al.(Hobbs,
Dekkers, & Watkins, 1988) followed their work and employed this method to predict and
interpret composite-droplet morphology of ternary polymer blends. The modified Harkins
equation can be written as:
Equation 2-30. λij = γ jk − γ ik − γ ij
λ is defined as the spreading coefficient giving the tendency of component (i) to encapsulate or
ij
spread onto component (j) in the matrix of component (k). γ , ij γ , and jk γ are the interfacial
ik
tensions of the different polymer pairs. Two different morphologies can be obtained, depending
on the values of the spreading coefficients, as spreading is predicted to occur only for positive
values ofλ . In other words, a positive value of one of the spreading coefficients such asλ ij
ij
indicates wetting of phase j by phase i. This case is called complete wetting morphology and is
shown in Figure 2-3. The other possible prediction is partial wetting in which all spreading
coefficients have negative values. In this morphology all phases have interfaces with each other
(Figure 2-3).
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