a) b - École Polytechnique de Montréal

2.1 Polymer Blends
CHAPTER 2 - LITERATURE REVIEW
One of the most important ways to make novel, high performance polymer materials over the last
40 years has been polymer blending, which has found applications in many different scientific
fields. By using this method, many properties such as electrical, mechanical, physical and other
properties can be combined in a material and adjusted to the needs of particular end-use
applications (Hara & Sauer, 1998), although blends are also used for manufacturing polymeric
materials at lower cost or with improved processing behaviour. Polymers are macromolecules
with high molecular weight and particular structures; thus, most of them do not have favorable
interactions with each other.
There are two different groups of polymer blends: miscible and immiscible polymer blends. The
former are homogeneous and stable with intermediate properties. The latter group represents the
majority of polymers, with morphology-dependent properties. When polymers are mixed, a
phase-separated mixture is formed.
2.1.1 Miscible Polymer Blends
Development of thermodynamics of binary mixtures of low molecular weight liquids followed
by study of miscibility of a binary polymer blend started in the 19 th century. For over 50 years,
the cornerstone of polymer solution thermodynamics has been the Flory-Huggins model.
Theoretical equations of state for polymer liquids were explained in the mid-1960’s by Flory and
co-workers (Flory, 1965; Flory, Orwoll, & Vrij, 1964).
Thermodynamics determine the equilibrium states that can be achieved for any given set of
conditions when two polymers A and B are mixed together. Gibbs(Gibbs, 1876) formulated the
stability of multiphase systems in terms of the quantity G defined as follows:
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