Dilatometric detection

The dilatometric methods for detecting phase changes utilize volume changes in the same way as the calorimetric methods utilize thermal effects. Dilatometry is widely used in the analysis of melts and particularly of fats and waxes (Bailey, 1950 Swern, 1979). The techniques and equipment are usually quite simple. 

Employing a dilatometric technique, Booth and coworkers determined the melt behavior of fractionated PPO as a function of crystallization temperature and by this technique found the thermodynamic melting point for PPO to be near 82° (Fig. 31), surprisingly 100° C lower than that of POM. These authors also detected three dilatometric transitions for partially isotactic material. The first below 60° was ascribed to the melting of lamellar crystals of limited thickness arising from the isotactic sequence. The other two transitions which depended on Tf- were attributed to the melting of lamellae with thicknesses determined by primary nudeation. 

If the pressure coefficient and the enthalpy of the transition are known, the volume change of the transition can be calculated. From the value obtained above for the latent heat, Equation (1) predicts a volume increase, SV/V, of order 0.1 % at the LCOT for the Mw=85K P(rf-S-Ii-nBMA) at atmospheric pressure. To confirm the volume change experimentally, dilatometric techniques are usually employed, where mercury displacement in a fine bore capillary provides the high precision necessary to detect such small changes. Although dilatometry studies are in progress, x-ray reflectivity was employed as an altmiative route to access bV/V experimentally where a high precision in the measurement of thickness can be achieved. 

The monitoring of any property that is sensitive to the glass transition phenomenon can be used to measure Tg however, the variations of these properties are generally very difficult to detect, and only techniques based on dilatometric, calorimetric, or... 

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