Glass-Rubber Transition and Melt Flow

J t) has a characteristic shape composed of several parts. Subsequent to the glassy range with a sohd-like compliance in the order of 10 N m, an additional anelastic deformation emerges and eventually leads to a shear compliance in the order of 10 m. The latter value is typical for a rub- 

These are the basic ingredients determining the mechanical properties of amorphous polymers and we now discuss them in a brief overview. 

A first important conclusion can be drawn immediately it concerns the nature of the main part, the glass-rubber transition. As we find a systematic shift of the time range of the transition with temperature, it is obvious that we are dealing here with a purely kinetical phenomenon rather than with a structural transition like the melting process or a solid-solid phase change. Curves demonstrate that whether a sample reacts like a glass or a rubber is just a question of time. Temperature enters only indirectly, in that it determines the characteristic time that separates glassy from rubbery behavior. 

The measurements at high temperatures in Fig. 6.11 indicate a viscous flow with a constant creep rate, determined by a viscosity r/o 

The KWW function employs two parameters t sets the time scale and / determines the extension in time of the decay process. For values / 1 a broadening results, as is always observed for the glass-rubber transition. Typical values are in the order / 0.5. The KWW function holds only at the beginning, i.e., in the short-time range of the glass-rubber transition. Subsequently, there often follows a power law 

J(t) has a characteristic shape composed of several parts. Subsequent to the glassy range with a solid-like compliance in the order of 10 N m, an additional anelastic deformation emerges and eventually leads to a shear compliance in the order of 10 N m. The latter value is typical for a rubber. For a certain time a plateau is maintained but then there finally follows a steady linear increase of J, as is indicative for viscous flow. The displayed creep curve of polystyrene is really not a peculiar one and may be regarded as representative for all amorphous, i.e. noncrystalline polymers. One always finds these four parts 

In chapter 7, we will discuss the properties of rubbers. These are networks, composed of chemically cross-linked macromolecules. Owing to the weak restoring forces, application of stress here induces a deformation which is very large compared to solids. The observation of a plateau in the creep compliance at a height comparable to the compliance of rubbers indicates 

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