Interfaces and Interphases in Composites

Glass fiber reinforced polymers and resins have found widespread application as light weight construction materials. In addition, the properties of interfaces and. interphases play a crucial role in determining the ultimate mechanical and other properties in these and related applications. Since the corresponding length scales can be on the far sub-micrometer level, a more detailed insight requires local analysis techniques which provide materials contrast. 

Intermittent contact mode phase imaging is, similar to force modulation and pulsed, force mode, sensitive to differences in materials properties. In Fig. 3.67 (a), the stiffness difference between glass and a polymer-based matrix gives rise to excellent image contrast. In addition, the different components of the polymer blend can be recognized (compare schematic in Fig. 3.67 (b)). 

In a recent study, the interphases for different fiber/polymer matrix systems were investigated. By using phase imaging the differences in local mechanical property variation in the interphase of glass fiber reinforced epoxy resin (EP) and glass fiber reinforced polypropylene matrix (PP) composites could be unraveled. As shown in Fig. 3.68, the glass fiber, the interphase and the PP matrix can be differentiated based on their surface mechanical properties as assessed qualitatively by TM phase imaging. 

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