The Interphase Definition

From the early 1980s, it was well accepted that the desired performance of a polymer-based heterogeneous material would pass through a well-optimized interaction level across the interphases between the components (4). The interphase is defined as the dynamic and finite spatial region placed between the border of each of the two different phases where momentum, mass, and energy transport phenomena may occur. 

According to this figure, the interface would be obtained by projecting all volumes between both phases sensitive to the desired property onto a single and finite surface defined by a critical thickness, where any measured property would exhibit the sharpest possible change from one phase to another. So, different critical thicknesses for different properties or response functions can be expected. 

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