Differential scanning calorimetry glass-rubber transition

Poly(epichlorohydrin), CO rubber (Hydrin), was chosen for various reasons. The one reason was that CO has been shown to be miscible with PMMA by Anderson based upon differential scanning calorimetry (DSC) which showed only one glass transition temperature (T ) for the blend (9). Since T is very sensitive to the disruption of the local structure that results when two polymers are mixed, the existence of a single glass transition temperature is a good indicator of miscibility (10). 

Many relatively slow or static methods have been used to measure Tg. These include techniques for determining the density or specific volume of the polymer as a function of temperature (cf. Fig. 11-1) as well as measurements of refractive index, elastic modulus, and other properties. Differential thermal analysis and differential scanning calorimetry are widely used for this purpose at present, with simple extrapolative eorrections for the effects of heating or cording rates on the observed values of Tg. These two methods reflect the changes in specific heat of the polymer at the glass-to-rubber transition. Dynamic mechanical measurements, which are described in Section 11.5, are also widely employed for locating Tg. 

Burfield, D. R. and K. L. Ldm, Differential scanning calorimetry analysis of natural rubber and related polyisoprenes. Measurement of the glass transition temperature. Macromolecules, 16, 7, 1170-1175, 1983. 

Figure 2 shows the SVM images for the PS film collected at various temperatures from 200 to 400 K [23]. The surface modulus of the silicon substrate should be invariant with respect to temperature in the employed range, meaning that the contrast enhancement between the PS and Si surfaces with temperature reflects that the modulus of the PS surface starts to decrease. In the case of a lower temperature, the image contrast was trivial, as shown in the top row of Fig. 2. On the other hand, as the temperature went beyond 330 or 340 K, the contrast between the PS and Si surfaces became remarkable with increasing temperature. This makes it clear that the PS surface reached a glass-rubber transition state at around these temperatures. Here, it should be recalled that the T of the PS by differential scanning calorimetry (DSC) was 378 K. Therefore, it can be claimed that surface glass transition temperature (7 ) in the PS film is definitely lower than the corresponding T. ...

Note r , dynamic mechanical peak temperature for glass transition (1 Hz) Tg, calorimetric glass transition temperature Pkww. KWW distribution parameter for glass-rubber relaxation FE V, fractional fiee volume based on density measurements DSC, differential scanning calorimetry. 

Thermal characterization of an emulsion polymer essentially means the measurement of the glass transition temperature Tg, that is the temperature above which the hard, glass-like polymer film becomes viscous or rubber-like. Polymers whose Tg lies well above room temperature are designated as hard , those with a Tg much lower than room temperature as soft . Normally Tg is measured by differential scanning calorimetry (DSC [25]). In this technique, the difference between the heat absorbed per unit time by the polymer film to that absorbed by a thermally inert reference material is recorded during a linear temperature ramp. The sample and the reference are placed on a sensor plate of defined thermal resistance R, and the temperature difference AT between the sample and the reference is then recorded over the temperature ramp. Usually, the heat flow difference, which is the negative quotient of AT and R, is plotted as a function of temperature (Fig. 3-11). 

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