Crystalline temperatures

One possible reason suggested by Flory and Mandelkern (1956) for or contribution to the discrepancies indicated in Table 2 is the inability of the penetrometer method to detect the maximum temperature of melting because of its relative insensitivity and because of the upper "tail to the crystallinity-temperature curve as deduced from the copolymer crystallinity theory of Flory (1955). Dole and Wunderlich (1957, 1959) found, however, that two melting regions each of the quenched 80/20 and 60/40 copolymers could be observed in the calorimetric experiments. The specific heat curves of these two copolyesters are illustrated in... 

FIG. 13.5 Storage shear modulus for polyethylene terephthalate) with different degrees of crystallinity temperature. From McCrum, Buckley and Bucknall, 1988. Courtesy Oxford University Press. 

Solute (tracer) crystalline Temperature Form of energy. Q. factor. Do. Reference... 

Microporous silicas with pore size of 12.2 A were prepared by either S XT or S " pathways at room temperature using dodecyidimethylbenzylammonium chloride (DDBAC) surfactant. The pore size of the synthesized materials could be tuned from microporous to mesoporous range by the crystalline temperature or using mixed surfactants of DDBAC and cetyl-pyridinium chloride. The pore structure can transfer from disordered tubular array to ordered hexagonal phase by the increase of the molar ratio of CPCl to DDBAC. 

As found for the hexakis(alkanoyloxy) benzenes with oxa or thia atoms inserted along the chains [113,114], thia ethers of the analogous IS have smaller liquid crystalline temperature ranges and higher clearing points than the corresponding IS oxa ethers [115]. 

One is the classical method based on photoselection and rotational diffusion in the steady state of the cis-trans photoisomerization, which includes irradiating with linearly polarized 365 nm light and subsequent annealing in the liquid crystalline temperature range of the film. The spacer length and exposure dose significantly influence the reorientation direction. In-plane reorientation... 

FIGURE 11.2. Plot of melting temperature against crystallization temperature for poly(ethylene oxide), ( ) high crystallinity o low crystallinity. Temperature in degrees Celsius [18]. 

Allow the sample to cool at the same rate as that of heating, to the estimated crystalline temperature (115-135 °C). 

Maintain the crystalline temperature, and obtain an isothermal crystallization DSC curve as shown in Figure 4.16. 

Annealing of semicrystalline polymers is a difficult process to understand. Both microscopic and macroscopic defects are reduced upon sample exposme to temperatures somewhat below the crystalline temperature. Polymer crystals are metastable, ie the lamellae thickness and lateral size are generally determined by the degree of supercooling balanced by the side and end free energies. Therefore, as a function of time, chain-folded polymer crystals thicken on annealing to minimize the number of folds. Although the exact mechanism has yet to be determined... 

All the compounds were obtained estoification of the corresponding dicarboxylic acids with diolesterol and die correqionding hydro azobenzenes. The phase transition tonperature was obso ved DSC measurements ( 2 "C min rate of temperature change). The reflectim spectra were measqred for the films by dipping the sample in ice water before or after irradiation at the liquid crystalline temperature. 

The nature of the electrochemical reactions in a cell, especially with d.c. drive, depends amongst other factors on the molecular constitution of the nematic substances, on impurities in the liquid crystal and on the conductivity and orientation additives [84]. Even the electrodes and substrates, their contamination and the drive voltage and its duty cycle can also affect these reactions. The primary failure mechanisms are breakdown of the surface alignment, formation of bubbles, discoloration of the liquid crystal layer or a narrowing of the liquid crystalline temperature range. 

The apparent melting temperature, Tm, the crystallinity temperature, Tc, and the crystallinity index, a, of all the samples were measured via Differencial Scanning Calorimetry (DSC)... 

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