Ideal chains Debye-structure function

Fig. 2.9. Debye-structure function of an ideal chain with size Ro...

Sd is known as the Debye-structure function of an ideal chain, and a plot is shown in Fig. 2.9. In correspondence to the pair distribution function, the Debye-structure function can also be expressed in a reduced form, with v as general variable. Both the equations for the pair distribution function and for the scattering law indicate that all ideal chains are similar to each other, differing only in the length scale as expressed by Rq. 

Figure 2.13 shows the result of a light scattering experiment on the same system, a dilute solution of polystyrene (Mn = 8.79 10 ) in cyclohexane. The measurement was conducted exactly at the theta-point. As we have learned, ideal chains scatter according to the Debye-structure function, with the asymptotic limit Sd The data display the product... 

On the other hand, for this case the exact form of 5c is known. Since in melts polymer chains are ideal, Sc is given by the Debye-structure function (Eqs. (2.60) and (2.61)), multiplied by the volume fraction in order to account for the dilution... 

The continuous lines, which give perfect data fits, represent Debye structure functions (with minor corrections to account for polydispersity effects), thus proving the ideal behavior of chains. In addition, intensities were found to be proportional to the weight fraction of deuterated chains... 

The structure of g(q) for ideal chains was discussed first by Debye,and thus we call g(q) the Debye function gi>(q). 

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