Melting transition temperature measurement

Fig. 11. Evidence that a membrane-associated immunochemical reaction (complement fixation) depends on the mobility of the target hapten (IX) in the plane of a model membrane. The extent of the immunochemical reaction, complement fixation, is measured by A Absorbance at 413 nm. Temperature is always 32°C, which is above the chainmelting temperature (23°C) of dimyristoylphosphatidylcholine used for the data given in A and below the chain-melting transition temperature (42°C) of dipalmitoylphosphatidyl-choline used for the data in B. Thus A refers to a fluid membrane and B refers to a solid membrane. The numbers by each curve are equal to c, the mole % of spin-label hapten IX in the plane of the lipid membrane. It will be seen that complement fixation, as measured by A Absorbance at 413 nm is far more effective in the fluid membrane than in the solid membrane at low hapten concentrations (i.e., c 0.3 mo e%). In C the lipid membrane host is a 50 50 mole ratio mixture of cholesterol and dipalmitoylphosphatidylcholine. The immunochemical data suggest that this membrane is in a state of intermediate fluidity. Specific affinity-purified IgG molecules were used in these experiments. (For further details, see Ref. 5.)... 

Griffith, J. H., and B. G. RA.nby Dilatometric measurements on poly (4-methyl-l-pentene), glass and melt transition temperatures, crystallization rates and unusual density behavior. J. Polymer. Sci. 44, 369—381 (1960). 

Water absorption of the resultant cured materials was measured after immersion for 24 hrs at room temperature and reported as % weight gain. The modulus was measured according to ASTM D 2240, and the dielectric constant and dissipation factor were measured using a method similar to ASTM D 150. Glass and melting transitions were measured by differential scanning calorimetry (DSC). The thermal stability was determined in a forced air oven... 

Two examples of the use of localised thermal analysis are provided in order to illustrate the generic applications of this approach. Figure 8 shows localised thermomechanical analysis of the surface of the multi-layer film in Figure 4. Measurements were made at points within this image describing the bulk polymer, the central gas-barrier layer and the thin tie-layer between this and the bulk film. The melting transition temperatures are consistent with high density polyethylene, poly(ethylene-co-vinyl alcohol) and medium density polyethylene for the bulk, gas barrier and tie layers, respectively [101],... 

Semicrystalline polymers exhibit a melting transition temperature (Tm), a glass transition temperature f Tg) and crystalline order, as shown by. . lay and electron scattering. The fraction of the crystalline material is determined by x-ray diffraction, heat of fusion and density measurements. Major structural units of semi-crystalline polymers are the platelet-like crystallites, or lamellae, and the dominant feature of melt crystallized specimens is the spherulite. The... 

Isotactic polystyrene can also be obtained in an amorphous modification at low temperature by quenching to below the glass transition temperature from above the melting temperature. Only Abu-Isa and Dole (1965) and Karasz, Bair, and O Reilly (1965) measured the heat capacity of amorphous isotactic polystyrene below the melting transition. Both measurements show almost identical values to the atactic sample and also a similar glass transition temperature. At about 400° K the amorphous isotactic sample is not metastable any more, but crystallizes slowly to become semicrystalline. 

The heat capacity of liquid macromolecules can be measured above the glass-transition or the melting-transition temperature. The group vibrations change little on fusion. The changes of the skeletal vibrations due to volume... 

PVF displays several transitions below the melting temperature. The measured transition temperatures vary with the technique used for measurement. T (L) (lower) occurs at —15 to —20 " C and is ascribed to relaxation free from restraint by crystallites. T (U) (upper) is in the 40 to 50°C range and is associated with amorphous regions under restraint by crystallites (63). Another transition at —80° C has been ascribed to short-chain amorphous relaxation and one at 150°C associated with premelting intracrystalline relaxation. 

As-polymerized PVDC does not have a well-defined glass-transition temperature because of its high crystallinity. However, a sample can be melted at 210°C and quenched rapidly to an amorphous state at <—20°C. The amorphous polymer has a glass-transition temperature of — 17°C as shown by dilatometry (70). Glass-transition temperature values of —19 to — 11°C, depending on both method of measurement and sample preparation, have been determined. 

The ability of XPD and AED to measure the short-range order of materials on a very short time scale opens the door for surface order—disorder transition studies, such as the surface solid-to- liquid transition temperature, as has already been done for Pb and Ge. In the caseofbulkGe, a melting temperature of 1210 K was found. While monitoring core-level XPD photoelectron azimuthal scans as a function of increasing temperature, the surface was found to show an order—disorder temperature 160° below that of the bulk. 

The glass transition temperatures of the nylons appear to be below room temperature so that the materials have a measure of flexibility in spite of their high crystallinity under general conditions of service. The polymers have fairly sharply defined melting points and above this temperature the homopolymers have low melt viscosities. Some thermal properties of the nylons are given in Table 18.4. 

Two crystalline forms have been observed.One is formed by slow cooling from the melt and the other by slow heating of the amorphous polymer. The properties of the commercial products were therefore to some extent dependent on their heat history. Glass transition temperatures observed range from 7 to 32°C and depend on the time scale of the method of measurement. ... 

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