Crystal-matrix interface

Second, the molecular orientation of the fiber and the prepolymer matrix is important. The rate of crystal nucleation at the fiber-matrix interface depends on the orientation of matrix molecules just prior to their change of phase from liquid to solid. Thus, surface-nucleated morphologies are likely to dominate the matrix stmcture. 

In the present work, we study ice crystal growth in AFGP solutions with phase contrast and fluorescence microscopies in a 1-directional growth apparatus. With fluorescence microscopy we have directly visualized the protein dynamics at the interface of a growing ice crystal. Contrary to previous understandings, the proteins become incorporated into veins and not directly into the crystal matrix." This indicates that the proteins only weakly adsorb to the interface. Under slower growth conditions no veins are... 

So, if the interfacial regions have to be considered, we must differentiate the amorphous/crystal polymer interface from the amorphous polymer/mineral interface (29). By DMA measurements, a decrease in Tg matrix from 7°C for the PP/talc composites and also for the neat PP processed under similar conditions while a decrease upto 13°C was found for PP/mica composites. A higher fraction of free amorphous phase on the PP/mica system than on the PP/talc composites was evidenced. This free amorphous phase appeared to participate in the cooperative segmental free-rotation motion, well accepted (30) to be responsible for glass transition for the polymer matrix as fully discussed in Reference 29. 

Figure 7.18 shows schematic crack paths through (a) water ice and (b) ice cream. The weakest part of the water ice microstructure is the ice-matrix interface, so the crack follows a path along the edges of the ice crystals as far as possible. In the ice cream, the air bubbles are the weakest links so the crack passes through them. The ice crystals are the most fracture-resistant components so in both cases the crack passes around them. Ice cream is effectively a particulate-reinforced composite material, i. e. a material in which tough particles are embedded in a relatively soft continuous phase in order to increase the overall fracture resistance. Since the microstructure is heterogeneous, it is not possible to predict exactly where the crack will form or precisely what path it... 

It is known that alkali treatment improves the fiber-matrix adhesion due to the removal of natural and artificial impurities from the fiber surface as well as the change in the crystal structure of the cellulose [119]. Moreover, alkali treatment reduces fiber diameter and thereby increases the aspect ratio. Therefore, the development of a rough surface topography and enhancement in aspect ratio offer better fiber-matrix interface adhesion and an increase in mechanical properties was reported by Mohanty et al. [68]. Alkali treatment increases surface roughness resulting in better mechanical interlocking due to the amount of cellulose exposed on the fiber surface [53]. Several other studies were conducted on alkali treatment and the results are discussed elsewhere [36, 37, 41, 86]. 

Carbon fibers and glass fibers act as heterogeneous nucleating agents and nucleate crystallization along the fiber-PEEK matrix interface. ... 

An interesting application of surface-induced alignment of LCTs is orientation at the surface of fibers in fiber-reinforced composites. Adams and Mallon have shown that a low molar mass liquid crystal is oriented at the surface of a carbon fiber parallel to the fiber direction (111), while Sue and co-workers foimd that 1 can be oriented along the fiber direction, depending on the cure schedule and the epoxy/hardener formulation (112). These findings raise the possibility of creating fiber-reinforced composites with controlled matrix orientation and/or tailored interfaces, which may improve the fiber/matrix interface and result in improved properties (see Reinforcement). 

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