Experimental Observation of the Coil-Globule Transition

There have been a fair nmnber of experiments on the coil-globule transition with decreasing temperature. The most detailed studies were carried out by scientists from three laboratories. One was the group of E. Anufrieva at the Institute of High Polymers in St. Petersburg where they used a polarized 

Some other methods have also been employed to observe the coil-globule transition for isolated polymer molecules (e.g., ordinary light scattering, viscosity and osmotic pressure measurements, and elastic neutron scattering off polymer solutions). However, the two techniques we mentioned before are the best for this purpose. They are very sensitive and allow measurements of solutions at extremely low concentrations. 

Despite various tricks, the problem of chain aggregation has not quite been solved. The experts still argue. Research continues, and experimentalists have now reached remarkably low concentrations. In fact, at these concentrations averaged macromolecule has to diffuse for almost ten minutes before it meets another macromolecule. It seems then that the most promising direction for further studies is to try making all measurements within these ten minutes, before macromolecules can aggregate 

Very interesting experimental results on the coil-globule transition were obtained by the group of K. Yoshikawa in Kyoto by taking DNA instead of a synthetic polymer. We will discuss this a little further in the Section 9.12. 

---

The literature reports failure in experimental observation of the coil-globule transition as well. Kg. Hauer and Ullman (1980) measured R// of polystyrene macromolccules in cyclohexane (iVf =510. .. 4.4 lO with a narrow MWD, within a concentration range 0.150... 0.001%) by means of photon correlation spectroscopy (dynamic light scattering). When T < 9. Ru linearly diminishes with lowering temperature, and no coil-globule transition was detected. 

---