Differential scanning calorimetry liquid crystals

Peripheral modification of the receptor molecules may allow the existence of stacking structures in soft materials such as thermotropic liquid crystals. Differential scanning calorimetry (DSC) analysis of the octane xerogel of Ic Cl -TATA+ suggested the formation of a mesophase as observed in the phase transitions at 88 and 42°C upon first cooling from the isotropic liquid state (Iso) and at 44 and 96°C upon second heating. 

The results of differential scanning calorimetry(DSC) indicate the change in aggregation state. The trans micelle showed a main endothermic peak at 14 2°C(A H =1.0 kcal/mol), corresponding to a gel-liquid crystal phase transition, whereas the transition temperature for the cis micelle appeared at 11.9°C( AH = 0.8 kcal/mol). This is unequivocal evidence that the trans-cis photoisomerization is a sufficient perturbation to alter the state of molecular aggregation. 

Stratum corneum lipids and lanolin share an important physical characteristic in that they can coexist as solids and liquids at physiological temperatures.33 A differential scanning calorimetry thermogram of lanolin is similar to that of stratum corneum lipids, showing two broad (heterogenous) phase transitions with midpoint melting temperatures at 21.9 and 38.3°C.16 The lower temperature peak may represent the transition from a liquid crystal to a gel phase, which has also been described for lanolin alcohols.34... 

Differential Scanning Calorimetry (DSC) is a sensitive way of detecting phase transformations of a bulk material [85,86]. Monitoring the thermal behavior of a crystal or a powder as a function of its conversion to product can give important information. This technique can verify whether a reaction occurs in a purely solid phase or whether there may be liquid phases involved at a given temperature. Melting point depression can be monitored as product appears, and the characteristic melting of a new phase can be detected if one is formed. DSC can reveal whether or not a eutectic transition attributable to a mixture of phases is present. We have also used DSC in our lab to monitor the thermal stability of reactive crystals. 

Lee et al. (1996) applied step-wise crystallization fractionation to SME and reported similar results (Table 1.5). The liquid fraction had a total saturated FAME content = 5.5 wt% and crystallization onset temperature = -7.1 °C (determined by differential scanning calorimetry (DSC), compared to values of 15.6% and 3.7 °C before fractionation. Liquid product yield was also relatively low (25.5%). 

A similar thermally-induced inversion of the cholesteric sense was observed for the PBLG liquid crystal in benzyl alcohol. In this solution, a gel-like opaque phase coexists with the cholesteric phase at lower temperatures. The opaque phase disappears around 70 °C, where endothermic peaks are observed in the differential scanning calorimetry curve. The value of S below 70 °C remains constant, and then changes with temperature above 70 °C. The compensation occurs at about 103 °C, and the transition from biphasic phase to the isotropic phase is observed above 150 °C in this case. The results are summarized in Fig. 12, where the reciprocal of the half-pitch is plotted against temperature. The sign of 1/S is taken as positive when the cholesteric sense is the right-handed. 

Characterization. The liquid crystalline properties of the side-chain monomers (III) and polymers (I) have been studied by Differential Scanning Calorimetry (DSC), Polarized Optical Microscopy (POM) and X-ray diffraction. The thermal transition data and phase types for all monomers (III) and polymers (I) are summarized in Table HI. A representative DSC scan for the monomer (El) and polymer (p with a four-carbon tail (n=4) and six-carbon flexible spacer (m=6) are shown in Figures 1 and 2 respectively. The first peak at -24°C shown in Figure 1 is the crystal to smectic... 

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