Differential scanning calorimetry liquid crystals studied using

A complete characterization of liquid crystalline polymers should include at least two aspects the characterization of the molecular structure and that of the condensed state structure. Since the first characterization is nothing more than what is practiced for non-liquid-crystalline polymers, we will restrict the discussion to only a short introduction of methods mostly used in the characterization of the presence and the main types of polymeric liquid crystal phases. The methods include the mostly used polarizing optical microscopy (POM, Section 4.1), differential scanning calorimetry (DSC, Section 4.2) and X-ray diffraction (Section 4.3). The less frequently used methods such as miscibility studies, infrared spectroscopy and NMR spectroscopy will also be discussed briefly (Section 4.4). 

Differential scanning calorimetry was used to study the non-isothermal crystallization behavior of blends of poly(phenylene sulfide) (PPS) with the thermotropic liquid-crystalline copoly(ester amide) Vectra-B950 (VB) [126], The PPS crystallization temperature and the crystallization rate coefficient increased significantly when 2-50% VB was added. The Ozawa equation was shown to be valid for neat PPS as well as for the blends. The values of the Avrami exponents matched well against those determined previously using isothermal analysis, and they are independent of the concentration of VB. 

Calorimetric Methods.—Differential Scanning Calorimetry (d.s.c.). The use of commercially available d.s.c. apparatusto study phase separation in polymer and copolymer solutions is described. In this context perhaps the main advantage of the method is to distinguish between liquid-liquid phase separation, where the enthalpy change is usually small, and crystallization of polymer (see Chapter 12). The method is much used to study the glass transition in polymer mixtures (see p. 320). 

Nishikawa, K., Wang, S.L., Endo, T. and Tozaki, K., Melting and crystallization behaviors of an ionic liquid, l-isopropyl-3-methylimidazolium bromide, studied by using nanowatt-stabilized differential scanning calorimetry. Bull. Chem. Soc. Jpn. 82 (7), 806-812 (2009). 

Methyl cellulose is a derivative of cellulose soluble in water and widely used as a binder or thickener in pharmaceutical products, food products, in the field of ceramics, etc. Formation of the liquid crystal phase is dependent on molecular weight, concentration and temperature, as evidenced in different experimental studies employing differential scanning calorimetry, polarized light microscopy, optical rotatory dispersion [121]. This cellulose derivative has two stages of thermoreversible gelation in aqueous solution, as temperature rises, if concentration exceeds a certain critical value [117, 122]. Several studies [123] have revealed a crystal liquid phase in dilute solutions as well. 

Nishikawa, K, Wang, S., Endo, T., Tozaki, K. (2009) Melting and Crystallization Behaviors of an Ionic Liquid, l-Isopropyl-3-methylimidazolium Bromide, Studied by Using Nanowatt-Stabilized Differential Scanning Calorimetry, Bull. Chem. Soc. pn. Vol. 82 806-812. 

Differential scanning calorimetry (DSC) is by far the most commonly used thermal technique for studying liquid crystals. It is a very useful and sensitive survey technique for discovering new phase transitions and for determining the qualitative magnitude of thermal features. However, DSC is not well suited for making detailed quantitative measurements near liquid crystal phase transitions. 

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