Anisotropic melting temperature

A hot-stage-equipped polarizing microscope was used for measurement of these parameters. The anisotropic melting temperature (Tn) was determined as the onset temperature of stir-opalescence observed on the hot-stage. The liquid crystalline-isotropic transition temperature (71) was also determined by the use of the hot-stage-equipped microscope. 

A variety of relaxation time studies have been performed on toluene. The choice of deuterated toluene avoids certain complicating factors which affect proton NMR studies, such as, dipolar or spin-spin couplings. The dominant relaxation mechanism is quadrupolar and the relaxation times are determined by the reorientation of the C-D bond vector. Relaxation times such as T, are sensitive to the motions of the solvent around the larmor frequency, which is on the order of 14 MHz in this study. T2 measurements may probe slower motions if the molecule undergoes slow and/or anisotropic motion. The relaxation time results presented in Figure 3 are significantly shorter than those found in bulk toluene solutions (18.19). In bulk toluene, the T and T2 values are equal above the melting temperature (1.2.). In this polymer system T2 < T indicative of slow and/or anisotropic reorientation. 

Figure 3 describes reaction schemes for naphthalene carbonization catalyzed by metallic potassium or by aluminum chloride (13,14) these catalysts produce contrasting isotropic and anisotropic carbons, respectively. The intermediate structures are similar except for more naphthenic structure induced in the AlCl -catalyzed carbonization. The role of naphthenic structures leading to optical anisotropy has been recognized in many examples, and their introduction can improve the anisotropic development, as described later. Higher fusibility, lower melting temperature, and higher solubility of the intermediate molecules may be obtained by the formation of partially naphthenic structures (15). 

Wissbrun earlier observed a very long relaxation time and high elasticity for anisotropic melts of aromatic polyesters, as well as several other types of flow anomalies. Unfortunately, in most of these earlier studies, the rheological behavior of liquid crystal melts of polymers could not be directly compared with that of the isotropic phase of the same polymers because of their high clearing temperatures. 

The substituted polyamides with long alkyl- and alkoxychains [33] are highly soluble and form anisotropic melts above their melting temperature. These polyamides are typical examples of sanidic liquid crystalline polymers. Generally, no lyotropic behavior is observed. The temperature stability is obviously substantially lowered due to the substitution with alkyl chains. 

Specifically, silica melts and fibers have a uniform anisotropic network structure. The uniformity of this network structure causes a linear increase of the log melt viscosity with decreasing melt temperature. The anisotropy of the network structure, however, affords a relatively low fiber modulus. Two examples, admittedly extreme cases, may conceptually document the effect of disrupting the uniform anisotropic silica network structure by the addition of other oxides. 

Abstract. We performed depolarized light scattering (DPLS) and polarized optical microscope (POM) measurements on the strnctnre formation process or the crystallization process of isotactic polystyrene (iPS) nnder shear flow below and above the nominal melting temperature Tm- It was found in the DPLS measurements that an anisotropic oriented structure on a pm scale was formed even above the nominal melting temperature. This was also confirmed by POM measurements. This oriented structure must be a precursor of primary nucleation, at least, in the early stage of the formation process. The structure and its formation mechanism are discussed based on the analysis of the DPLS data. 

---