Interface aggregate-matrix

Siham.Kamali-Bernard insa-rennes.fr, dkeinde85 yahoo.fr, Fabrice.Bernard insa-rennes.fr Keywords Concrete, mechanical behavior, interface, aggregate, matrix. 

The quantitative determination of the influence of the ITZ is essential for mechanical properties (strength and Young s modulus) and durability (porosity) of cement-based composites, but it is difficult to determine the values of bond between two adjacent materials in concrete. Moreover, all measures aimed at modification of the ITZ, like the application of some kinds of microfillers, have an impact on the properties of the composite material itself, and these effects make analysis of test results more complex. The measurements of the ITZ properties in artificial specimens do not allow all conditions to reproduce correctly and tests performed on specimens built from concrete and stone parts have not snpplied particularly useful findings. Tests performed by several researchers, for example, Roy and Jiang (1995) or Mindess and Rieder (1998) on specimens in which the ITZ was artificially created between concrete and stone parts did not supply results that may be directly used for analysis of the interface between matrix and aggregate grains in concrete. 

The cracks initiate and propagate in the form of decohesions in the aggregate-matrix interface and these regions deserve more particular attention. The physical and chemical composition, as well as the structure of the interface, is essentially different from these of the bulk matrix. Cracks are often arrested just at the interface layer a few micrometers before reaching an obstacle in the form of an aggregate grain or a fibre (cf. Chapter 7). 

Interfacial behavior of different silicones was extensively studied, as indicated in Section 3.12.4.6. To add a few more examples, solution behavior of water-soluble polysiloxanes carrying different pendant hydrophilic groups, thus differing in hydrophobicity, was reported.584 A study of the aggregation phenomena of POSS in the presence of amphiphilic PDMS at the air/water interface was conducted in an attempt to elucidate nanofiller-aggregation mechanisms.585 An interesting phenomenon of the spontaneous formation of stable microtopographical surface domains, composed primarily of PDMS surrounded by polyurethane matrix, was observed in the synthesis of a cross-linked PDMS-polyurethane films.586... 

Most reported zeolite/polymer mixed-matrix membranes, however, have issues of aggregation of the zeolite particles in the polymer matrix and poor adhesion at the interface of zeolite particles and the polymer matrix. These issues resulted in mixed-matrix membranes with poor mechanical and processing properties and poor separation performance. Poor compatibility and poor adhesion between the polymer matrix and the zeolite particles in the mixed-matrix membranes resulted in voids and defects around the zeolite particles that are larger than the micropores of the zeolites. Mixed-matrix membranes with these voids and defects exhibited selectivity similar to or even lower than that of the continuous polymer matrix and could not match that predicted by Maxwell model [59, 60]. 

Although a number of filler characteristics influence composite properties, particle size, specific surface area, and surface energetics must again be mentioned here. All three also influence interfacial interactions. In the case of large particles and weak adhesion, the separation of the matrix/ filler interface is easy, debonding takes place under the effect of a small external load. Small particles form aggregates which cause a deterioration in the mechanical properties of the composites. Specific surface area, which depends on the particle size distribution of the filler, determines the size of the contact surface between the polymer and the filler. The size of this surface plays a crucial role in interfacial interactions and the formation of the interphase. 

Another example of a Pc-based 1-D polymer is that reported by Armstrong and co-workers [158], They prepared a Pc with eight styrene-type polymerizable sites at the end of the peripheral substituents. This molecule forms highly ordered, rod-like aggregates at the air-water interface that can be transferred onto solid supports. Irradiation of the thin films affords polymerization between the olefin moieties of adjacent molecules by photostimulated [2 + 2] cycloaddition. The rod-like Pc macromolecules were conveniently studied by matrix-assisted laser desorp-tion/ionization (MALDI-TOF) spectrometry and atomic force microscopy (ATM), the latter showing rods with lengths up to 290 nm. 

As-synthesized MWCNT and SWCNT exist as bundles or ropes and tend to agglomerate due to strong van der Waals forces (13) (Figure 7.1). Unless the CNTs are separated in to individual tubes and dispersed in the polymer matrix, the interactions of the nanotubes with the polymer will be weak. The mechanical failure of such composites will occur due to slippage of the tubes in the bundle that are not bonded to the matrix. In addition, the aggregates or bundles reduce the aspect ratio of the reinforcement which affects electrical properties as well (15). Because of these factors the first step will be to open up these bundles to separate individual tubes by using different techniques to increase the volume of interface between the CNT and the matrix (40). 

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