MORPHOLOGY OF FILLED SYSTEMS

The crystalline structure of composite materials can be highly varied. The measurements of crystallinity show how the combined interference of the various components of the composite influences the structure. Filled material is composed of crystalline and amorphous regions separated by an interphase which is a diffuse boundary between these two states. The crystallinity of the binder material depends on the fraction of crystalline structures and on their size. Filler may affect both the fraction and the size of crystallites. But, those two measures of crystalline structure are often insufficient and the measurement of crystallinity may give confusing in-f ormation if the results are taken without further analysis of the fine structure of the material. Table 10.1 gives examples of the effect of fillers on material crystallinity from the current literature.  

Polymer Filler (%) Processing method Polymer crystallinity, % Composite crystallinity, % Reference 

It is difficult to conclude from the data in Table 10.1 whether the filler addition increases or decreases crystallinity. The lack of a clear pattern in the results is caused by differences in filler treatment and processing which cause the development of different structures as the material crystallizes. These points will be further discussed in the next paragraphs. 

Several studies have shown that small additions of filler cause substantial changes in crystallinity (either a large increase or decrease). Whether it was an increase or decrease in crystallinity, these small additions caused a substantial increase in tensile strength and a reduction in elongation. This indicates that the crystalline structure is formed by a nucleation process (see below) which is capable of producing reinforcement. 

Surface treatment of a filler may also affect crystallinity. Phosphate coating on talc increased the crystallinity at a low concentration of coating (up to 0.5%). But there was a decrease in crystallinity when the talc was coated with higher concentrations of phosphate.  

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This chapter analyzes how a filler is distributed in materials and what interaction occurs between the filler and the matrix. These two factors make a major contribution to reinforcement of the filled materials. We will outline the principles governing filler distribution and interaction and explain the relevance of reported studies. Chapters 5, 6, and 10 contain discussion of other related phenomena such as particle size of fillers, chemical reactivity in filled systems, and morphology, respectively. Chapter 8 shows impact of organization and filler presence on mechanical properties of filled systems. The information included in the above chapters helps us to understand how to use fillers to improve the performance of a material. 

Maiti and Bhowmick reported exciting results that a polar matrix like fluoroelastomer (Viton B-50) was able to exfoliate unmodified clay (Cloisite NA ) as well as the modified one (Cloisite 20A) [93]. They studied morphology, mechanical, dynamic mechanical and swelling properties of fluoroelastomer nanocomposites. The unmodified-clay-filled systems showed better properties than the modified ones (Table 2.3). 

In the case of layer compounds as electrode materials the kinetics of charge transfer were also studied in some detail taking into account surface recombination which plays an important role here . In the presence of suitable redox systems some materials show very little corrosion . This is due to the morphology of the crystal surfaces and it is generally assumed that corrosion occurs only at steps of different crystal planes . Accordingly, it is not surprising that the highest efficiencies were obtained with some of these materials (Table 1) . The steps also play an important role in the fill factor as determined by surface recombination measurements . ... 

Recently, Mitra et al. have prepared chemically crosslinked nanosized gels from different rubber lattices [148,149]. When added in small quantity (2-16 phr), these low moduli deformable gels have been found to influence the mechanical properties of virgin elastomers like NR and SBR considerably. For example, sulfur prevulcanized nanosized SBR latex gels were prepared and characterized using various methods [148]. The morphology of gel-filled NR and SBR systems has been studied... 

The process of mould filling should not be considered as completely understood and controlled 98>, though some important features of gas-filled system flow were established by Fridman and co-workers 99 100) who have explained the formation of laminated structures in low-pressure moulding of foaming melts and found the correlation between moulding conditions and morphologic macro-structure and properties of foam articles. 

Thus far, the most successful approach to M IP-based CEC utilises capillary columns filled with a monolithic, super-porous imprinted polymer [39-41]. The morphology of a certain MIP monolith is depicted in Fig. 16.3. Using this system enantiomer separations with baseline resolution have been carried out in less than 2 minutes. The M IP-filled capillaries are obtained by an in situ photo-initiated polymerisation process (Fig. 16.4]. The capillary is filled with a pre-polymerisation mixture of imprint molecule, functional and cross-linking monomers (MAA and TRIM, respectively), radical initiator (2,2 -azobisisobutyronitrile) and solvent (toulene). Both ends of the capillary are sealed and the polymerisation is performed... 

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