Polarizing microscopy composites

Characterization439 Inherent viscosity before and after solid-sate polymerization is 0.46 and 3.20 dL/g, respectively (0.5 g/dL in pentafluorophenol at 25°C). DSC Tg = 135°C, Tm = 317°C. A copolyester of similar composition440 exhibited a liquid crystalline behavior with crystal-nematic and nematic-isotropic transition temperatures at 307 and 410°C, respectively (measured by DSC and hot-stage polarizing microscopy). The high-resolution solid-state 13C NMR study of a copolyester with a composition corresponding to z2/zi = 1-35 has been reported.441... 

In summary, polarizing microscopy provides a vast amount of information about the composition and three-dimensional structure of a variety of samples. The technique can reveal information about thermal history and the stresses and strains to which a specimen was subjected during formation. Polarizing microscopy is a relatively inexpensive and well accessible investigative and quality control tool. 

Some recent examples demonstrating the molecular dispersion of rod polymer molecules in coil polymer matrices due to ionic interactions were given by Parker et al. (1996). These systems were based on three types of ionic PPTA s (Figure 5.4) and polar polymers, such as poly(4-vinylpyridine) (PVP), poly(vinyl chloride) (PVC), poly(ethylene oxide) (PEO), and poly(styrene-co-acrylonitrile) (S-AN). Due to the ionic-dipole interactions the rod-coil polymer pairs formed molecular composites as revealed by optical clarity, polarized microscopy, Tg measurements, as well as TEM observations. More significantly the molecular composites based on amorphous matrix polymers (e.g., PVP) were all transparent and showed no phase separation upon heating. Therefore they are melt-processible. As would expected, the mechanical properties of the molecular composites were... 

Triangles denote the compositions of SAXS samples measured here, whereas circles denote binodal points obtained by polarization microscopy. 

Figure 3. Polymer/monomer state diagram of p-methyl, p -acryloyloxyazoxybenzene obtained by polarizing microscopy Mp composition (weight fraction of polymer). Characteristic points ( ), decreasing birefringence CY), mesomorphic transition mesomorphic melting (%), solidus (O), liquidus. The meaning of the areas (A), isotropic liquid (B), isotropic liquid -j- mesomorphic plasticized polymer (C), liquid (D), glassy states of plasticized polymer in mesomorphic phase (E), crystalline monomer -f mesomorphic plasticized polymer in the glassy state (F), crystalline monomer -j-mesomorphic plasticized polymer in the liquid state (G), mesomorphic monomer -f mesomorphic plasticized polymer in the liquid state.

Scanning electron microscopy (SEM) has been used to characterize the physical and chemical interaction of fibres in FRC, as well as to address the durability of fibres. Microstructural analysis provides information on the corrosion of fibres, deposits of Portlandite surrounding fibres and the interaction between fibres and matrix (Purnell et al., 2000). Other techniques may be used as alternative to SEM. Uygunoglu (2008) has shown that polarizing microscopy is a suitable technique to assess the bond characteristics of steel fibres in SFRC, which is also related to durability of the composite. 

The effect of cellulose fiber surface treatment on the crystallization and interphase morphology of cellulose-polymer composites was studied using polarizing microscopy. Different nucleation patterns of the polypropylene matrix were observed, depending on the molecular structure of the coupling agent. 

Percec and coworkers [184] utilized a similar strategy for the conversion of perfluorinated alkylene functionalized 3,4,5-trihydroxy benzoic acid-type dendrons into methyl methacrylate functionalized dendritic macromonomers. Characterization of the resulting linear-dendritic architectural copolymers involved DSC, x-ray diffraction, and thermal optical polarized microscopy. It was concluded that the self-assembly of the pendant dendritic mesogens forced the linear backbone into a tilted, helical ribbon-type structure. The self-assembly behavior was largely controlled by the multiplicity, composition, and molecular weights of the pendant dendritic mesogens. 

Figures. The phase diagram of the DSCG/water system (as determined by hot stage polarizing microscopy). The double peritectic form of this diagram has come to be regarded as the classic chromonic pattern. Note, in particular, the characteristic sequence of phases formed by samples within the composition range indicated by the shaded band.

The melt mixed 80/20 PS/iPP blend displays a set of exotherms, where the amount of the iPP component that was heterogeneously nucleated is substantially reduced as indicated by the decrease of the crystallization enthalpy in the temperature region where the iPP crystallizes in bulk, i.e., at 109-111 °C (exotherm labeled A). This effect is due to the confinement of iPP into a large number of droplets. If the number of droplets of iPP as a dispersed phase is greater than the number of heterogeneities present in the system, fractionated crystallization occurs. The number of droplets for this composition is known (by scanning electron microscopy observations) to be of the order of 1011 particles cm-3 and polarized optical microscopy (POM) experiments have shown that this iPP contains approximately 9 x 106 heterogeneities cm-3. In fact, it can be seen in Fig. 1 that the fractionated crystallization of the iPP compon-... 

The fiber fragment length can be measured using a conventional optical microscope for transparent matrix composites, notably those containing thermoset polymer matrices. The photoelastic technique along with polarized optical microscopy allows the spatial distribution of stresses to be evaluated in the matrix around the fiber and near its broken ends. 

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