1. Introduction
Understanding the morphology of polymer blends is
important in order to determine relationships between the
structure and properties of materials. Microscopic methods like
light microscopy (LM), scanning electron microscopy (SEM),
low voltage scanning electron microscopy (LVSEM), transmission
electron microscopy (TEM) or atomic force
microscopy (AFM) can detect details, ranging from the
millimetre to the subnanometer scale, and are therefore popular
tools for visualising blend morphology: Table 1 [1]. In spite of
several spectacular developments in instrumental techniques,
structure determination of polymer blends remains a formidable
challenge. This is, because most electron microscopic
methods are based on observations on thin sections or surfaces
that show a cross-section of the three-dimensional structure or
only some surface topography that can be influenced by the
sample preparation method. These cross-sections are at best
two-dimensional projections of what is a 3D structure, in
essence discarding a third of all the spatial information that the
specimen may contain. Any specimen variation in the third
dimension can be minimised by careful sample preparation,
sectioning a specimen in a specific orientation to reveal the
features under study and/or by preparing two specimens from
mutually perpendicular axes. These approaches work best for
specimens with microstructures that are structurally simple,
such as a single-phase alloy. For most specimens, however, 2D
projections lead to some uncertainty as to their true 3D
structure. There are an increasing number of systems whose
functions are closely controlled by a complex 3D microstructure.
In such cases 2D projections can be at best inadequate, at
worst misleading. Because of these reasons, a single 2D
microscopic method is not sufficient for unambiguous
identification of the blend morphology and in the absence of
suitable 3D microstructure visualisation techniques; combinations
of several 2D-microscopy techniques are required.
In a blend of two polymers, if the major phase is dispersed in
the minor phase, the morphology becomes quite difficult to
identify experimentally. Such situations are quite common in
soft rubber–thermoplastic blends where the rubber phase is in
excess of the plastic phase. If, in addition the blends contain a
high volume percent of diluent such as paraffinic oil, which is