Morphology of Polymer Blends

The term of morphlogy refers to the shape and organization on a scale above the atomic level (e.g., the arrangement of polymer molecules into amorphous or crystalline regions) and the manner in which they are organized into more complex units. On the other hand, morphology of a polymer blend indicates the size, shape, and spatial distribution of the component phases with respect to each other. Since it is well established that most of the properties — mechanical, optical, rheological, dielectrical, and barrier properties of polymer blends are strongly influenced by the type and fineness of the phase structure, the study of the control of the morphology of polymer blends has emerged as an area of continuous interest to polymer material scientists in the last few decades. When two immiscible polymers are mixed, the size, shape, and distribution of one phase into the other depends on material parameters (i.e., blend composition, viscosity ratio, elasticity ratio, and interfacial tension) as well as on processing conditions (i.e., temperature, time, and intensity of mixing, and the nature of the flow). Therefore, the greatest challenge in the field of multiphase polymer blend research is the manipulation of the phase structure via a judicious control of the melt flow during processing and the interfacial interactions between the components.
Phase Domain
Region of a material that is uniform in chemical composition and physical state.
? Continuous Phase Domain (Matrix phase domain)
Phase domain consisting of a single phase in a heterogeneous mixture through which a continuous path to all phase domain boundaries may be drawn without crossing a phase domain boundary.
Note: In a polymer blend, the continuous phase domain is sometimes referred to as the host polymer, bulk substance, or matrix.
?Discontinuous Phase Domain (discrete phase domain,dispersed phase domain)
Phase domain in a phase-separated mixture that is surrounded by a continuous phase but isolated from all other similar phase domains within the mixture.
Note: The discontinuous phase domain is sometimes referred to as the guest polymer.

Figure 1 Phase Domain
Multiphase polymer blends may be divided into two major categories:
1. Blends with a discrete phase structure (i.e., droplets in matrix).
The morphology formation during melt-mixing of immiscible polymers involves processes such as liquid drops stretching into threads, breakup of the threads into smaller droplets, and coalescence of the droplets into larger ones. The balance of these competing processes determines the final particle size of the blends that results upon solidification of the blends. There are a variety of parameters that control the droplet and matrix morphology in polymer blends (Figure 2). These include the viscosity ratio, blend composition, elasticity ratio, shear stress, and interfacial tension.