Observation of the collapse of a polymer chain in poor solvent by small angle neutron scattering

The variation of the radius of gyration R of a polymer chain in an extremely dilute solution is measured as a function of the temperature T below the Flory temperature ϑ. The data are deduced from small angle neutron scattering experiments. In the temperature range studied two domains appear: In the first one (the ϑ region) R is rather independent of the reduced temperature τ[τ= (T−ϑ)/ϑ]. In the second one the collapse of the chain is observed and the τ dependence of R is R∼‖τ‖−0.32±0.05. The temperature variation of the second virial coefficient is also given. These results are discussed with regards to a possible demixion of the solution.