Glass transition temperature interactions

Other theories proposed dissipation of energy through crack interaction localised heating causing the material to be raised to above the glass transition temperature in the layers of resin between the rubber droplets and a proposal that extension causes dilation so that the free volume is increased and the glass transition temperature drops to below the temperature of the polyblend. 

In particular, blends of PVDF with a series of different polymers (polymethylmethacrylate [100-102], polyethylmethacrylate [101], polyvinyl acetate [101]), for suitable compositions, if quenched from the melt and then annealed above the glass transition temperature, yield the piezoelectric [3 form, rather than the normally obtained a form. The change in the location of the glass transition temperature due to the blending, which would produce changes in the nucleation rates, has been suggested as responsible for this behavior. A second factor which was identified as controlling this behavior is the increase of local /rans-planar conformations in the mixed amorphous phase, due to specific interactions between the polymers [102]. 

The argument assumes that the forces act only at the crosslinked ends of the strands. No interactions between the strands exist in this simplistic picture. The interaction of molecular segments, well above the glass transition temperature is usually rather small. 

As a consequence, the overall penetrant uptake cannot be used to get direct informations on the degree of plasticization, due to the multiplicity of the polymer-diluent interactions. The same amount of sorbed water may differently depress the glass transition temperature of systems having different thermal expansion coefficients, hydrogen bond capacity or characterized by a nodular structure that can be easily crazed in presence of sorbed water. The sorption modes, the models used to describe them and the mechanisms of plasticization are presented in the following discussion. 

Based on the behaviour of the glass transition temperature of the VIII/Li-Cl04/additives systems, it was suggested that the Li" ions interact preferentially with the CH3-(0CH2CH2)3- chains in the first case (crown ethers), and with azacrown in the second. This result also suggests that in case of azacrown, the anions are mainly responsible for conduction. 

Since the Lindemann ratio dija 0.1 is empirically roughly the same for all substances, one expects the g value, as measured by sound attenuation, to be correlated with the glass transition temperature. Note that this relationship is independent of the details of the bead assignment. Equation (20), if rewritten as Tg di/a) g, is almost obvious, given the interaction of the form in Eq. (17) The typical lattice displacement, at Tg, is roughly A< ) j- dija. On the other hand, the typical structural excitations have the energy of about Tg, at the glass transition. 

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