Homogeneous blends, critical

Fig. 16 Forced demixing of an initially homogeneous off-critical PDMS/PEMS blend for c = 0.3 (upper row) and c = 0.9 (lower row)...

With changing temperature the curves change for spinodals and binodals (the points of contact with the common tangent), plotted as T against q>, a picture as shown in Figure 9.3 may be obtained. In this case a lower critical solution temperature , LCST, exists, which is a maximum temperature at which, for every blending ratio, a stable homogeneous blend is possible. An upper critical solution temperature (UCST) may also exist in that case the curves are upside down. Besides, more complicated cases are possible (see also Qu. 9.4 tu. 9.7). 

The polyethylenes with higher functionality were soluble in epoxy resin and required lower temperamre and time for forming homogeneous blend systems. The miscibility of the polymers was dependent on the type of epoxy resin also. Cycloaliphatic epoxy resin showed more miscibility with the polymers compared to DGEBA resin and phase separation occurred in these blend systems as a result of crystallization of PE. Upper critical solution temperature (UCST) behavior was... 

Now about an LCST (lower critical solution temperature, see MT Figure 9.3). If we blend below this temperature, we can obtain a homogeneous mixture. Subsequent heating to above the LCST can resnlt in segregation the rapid cooling in an injection monlding machine does not allow to nndo this. 

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