Experimental conditions required to observe the collapse phenomenon

1 Experimental conditions required to observe the collapse phenomenon 

The demixtion curves (Fig. 16.2) show us that there exists a range of volume fractions q (cp tpc) and of temperatures T(T Tc) in which solutions are dilute and b is negative. Then for a fixed fraction q i, the predicted collapse (Chapter 14, Sections 3, 4, and 6) can be observed by lowering the temperature Tdown to the demixtion temperature T((p1). The process is schematically shown in Fig. 16.10. We can see that the smaller px is, the larger the domain of temperature to be explored will be however, the technical constraints of measurement require cp to be larger than a minimal value cplm below which observations are no longer possible. 

We shall examine here results of scattering experiments which will give us the gyration swelling XQ, extrapolated tQ concentration. 

the parameter S (the equivalent Brownian area of the polymer chains in the sample under study) has to be chosen so as to correspond to the best experimental conditions. In this connection, let us stress the following points  

The intensity increases proportionally to S. From this point of view, it is better to experiment with long chains. 

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