Deformation calorimetry

The only review which dealt with the polymer thermomechanics both in solid and rubbery state as inferred from deformation calorimetry was published in 1969 1). Our paper gives a review of further advances in this field. 

The above-mentioned method of deformation calorimetry has found a rather wide application. Modifications of the original design were constructed 72-75) and applied for investigating the thermomechanical behaviour of polymers and polymer composites. At the same time, the commercial Calvet-type calorimeters has been used in thermomechanical experiments on rubbers not only in the uniaxial mode 76-78 but also in torsion 79 80). Thus, deformation calorimetry has proved to be quite adequate in terms of sensitivity, specificity, rapidity and reliability and therefore seems to be the most promising experimental method of thermomechanical type. 

The thermomechanical data accumulated during the last years as a consequence of the improvement of the technique of deformation calorimetry contributed significantly to the understanding of thermodynamics and mechanisms of the reversible deformation of polymers in the glassy, semicrystalline and rubbery state. 

As with all other forms of plastic deformation in amorphous solids, we expect that in glassy polymers too the plastic deformation will consist of a series of discrete thermally assisted unit relaxation events on the atomic scale. Features of such discrete behavior have, e.g., been observed in deformation calorimetry by Oleinik (1991), who detected discrete unit inelastic events already in the pre-yield region in some glassy polymers. 

Adams, G. W., Farris, J. (1989). Latent Energy of Deformation of Amorpous Polymers. 1. Deformation Calorimetry. Polymer, i0(P), 1824-1828. 

Figure 6.11 shows a famous example of the application of isothermal calorimetry. Gordon (1955) deformed high-purity copper and annealed samples in his precision calorimeter and measured heat output as a function of time. In this metal, the heat output is strictly proportional to the fraction of metal recrystallised. 

The linear dependence on ks is a strong advantage compared to the force-modulation SFM. Due to the inertia of the cantilever mass at high frequencies, the tip cannot follow completely the displacement of the sample. This results in smaller elastic deformations and low forces in the pN range, which are measured by accelerated mass md2zldt2. Recently, the SLAM technique has been advanced toward variable temperature experiments [138]. Before this development, temperature ramps have been used to perform local calorimetry [139]. 

Empirical Relationship - Empirical relationships correlating glass transition temperature of an amorphous viscoelastic material with measurement temperature and frequency, such as the William Landel Ferry equation (17) and the form of Arrhenius equation as discussed, assume an affine relationship between stress and strain, at least for small deformations. These relationships cover finite but small strains but do not include zero strain, as is the case for the static methods such as differential scanning calorimetry. However, an infinitely small strain can be assumed in order to extend these relationships to cover the glass transition temperature determined by the static methods (DSC, DTA, dilatometry). Such a correlation which uses a form of the Arrhenius equation was suggested by W. Sichina of DuPont (18). 

It is important to select the components of the substrates with care and particularly to pay attention to the physical parameters they act upon, in particular the vitreous transition temperature (7g ) of the deep-frozen vaccine [20-25,30]. This temperature, also referred to as vitreous eutectic temperature, does indeed play a critical role in the deformation and collapsing of freeze-dried pellets [20,25], and possibly in the loss of infectivity titers. This temperature is dependent on the nature and concentration of the substrate molecules and may be determined in several ways [20,29,35,36]. In industrial practice, the most commonly utilized techniques are differential scanning calorimetry (DSC) as well as resistance and/or dielectric constant measurements. 

Similar changes can be found on the equatorial WAXS scans of drawn and annealed PEE (PBT/PEO = 57/43 wt%) taken at various tensile deformations (see Fig. 6.6). Once again, drastic changes, both with respect to the peak shape and peak angular position, can be detected at = 28.8 and 58.8%. The relative crystallinity Wc (for these drawn samples) from WAXS at various stages of sample deformation is presented in Table 6.3 since calorimetry or density measurements cannot be used for strained samples. 

After following the microhardness behaviour during the stress-induced polymorphic transition of homo-PBT and its multiblock copolymers attention is now focused on the deformation behaviour of a blend of PBT and a PEE thermoplastic elastomer, the latter being a copolymer of PBT and PEO. This system is attractive not only because the two polymers have the same crystallizable component but also because the copolymer, being an elastomer, strongly affects the mechanical properties of the blend. It should be mentioned that these blends have been well characterized by differential scanning calorimetry, SAXS, dynamic mechanical thermal analysis and static mechanical measurements (Apostolov et al, 1994). 

Dynamic mechanical analysis is routinely used to investigate the morphology of polymers, composites and other materials. The technique can be particularly sensitive to low energy transitions which are not readily observed by differential scanning calorimetry. Many of these processes are time-dependent, and by using a range of mechanical deformation frequencies the kinetic nature of these processes can be investigated. 

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