Gaussian-stretched coil transition

Fig. 7.36. Gaussian-stretched coil transition for PEP-PEE block copolymers as a function of the polymerization index. (Reproduced with permission from [213]. Copyright 1990 American Physical Society.)...

Fig. 7.36) indicate that departures from Gaussian statistics (8 = 0.5) are observed both in the ordered phase and in the disordered phase. This is consistent with the shift in position of the peak as the ODT is approached [212] and shows that the coils undergo a Gaussian-stretched coil transition in the disordered state, where 8 = 0.8=b 0.04. Such data have indicated the deficiencies of the original theory [208] and have subsequently been used as the basis for new theoretical developments [214-218]. This study indicates the close interaction between theory and experiment which has often been stimulated by the information provided by SANS over the past two decades. The possibility of measuring previously inaccessible parameters has stimulated theoretical developments, which have led to new experiments (e.g. Fig. 7.36), which have in turn prompted improvements in theory. 

K. Almdal, J. H. Rosedale, F. S. Bates, G. D. Wignall, and G. H. Fredrickson, Gaussian-to stretch-coil transition in block copolymer melts, Phys. Rev. Lett., 65, 1112 (1990). 

The conformational transition of the flexible macromolecules from a gaussian (or almost gaussian) coil to a stretched thread has often been employed as a convincing explanation of behaviours which were not predictable by more classical theories. 

As will be discussed in the next section, the shift of tf with increasing eN (Fig. 7.20) can be interpreted as resulting from an onset of chain stretching. While experimentally it was suggested that the transition from Gaussian coils to stretched chains that occurs at a temperature T above Tc is rather sharp, the more complete simulation data on this point show that this stretching of the chains sets in very gradually. 

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