No abstract

Neutron coherent scattering techniques have been used for the determination of the conformation of polymer in bulk and experimental details are given about the application of this method to the study of polymeric systems. Measurements have been made for small and intermediate momentum ranges on a series of eight monodisperse deuterated polystyrenes of molecular weight ranging from 21,000 to 1,100,000. The results lead to the concluson that in amorphous state the conformation of the polymer molecule is indistinguishable from that in solvent and that the Debye scattering function which is valid for unperturbed chains applies for q ~1 as low as 10 Á.

We report simultaneous measurements of the concentration profile and the free energy of the submerged PS blocks of PDMS-PS diblock copolymers spread as monolayers at the air surface of ethyl benzoate as a function of surface concentration. A parabolic concentration profile is found to give the best fit to neutron reflectivity curves among the set of two-parameter models examined. The maximum extension h*/Rf is comparable to previously reported values obtained from a variety of techniques for similar values of the reduced surface density a* and indicates some stretching perpendicular to the surface. As * increases from 1.3 to 4.2, the energy per PS block (obtained from surface tension measurements) increases sharply while the dependence of h* on a* is much weaker than the Vs power law dependence predicted for the strongly stretched regime. Thus, the energy required to stretch the chains for this system appears to be much larger than predicted by current theories.

Using the neutron scattering technique, we have measured the temperature dependences of the characteristic correlation lengths in semidilute polymer solutions in the vicinity of the theta (Θ) point. From the analysis of the data in the Guinier range, with a sample containing a few labeled chains, we find that the radius of gyration Rg has the dependence Rg∼τ0.125±0.005, where τ is the reduced temperature (T−Θ)/Θ. The scattering experiment from unlabeled samples, in the intermediate range of the momentum transfer, shows a decrease of the screening length ξ, ξ∼τ−0.25±0.01. These two dependences are in agreement with a recent calculation [M. Daoud and G. Jannink, J. Phys. (Paris) (to be published)] based on de Gennes’s theory that the theta temperature is in fact a tricritical point. A scaling law in molecular weight and concentration is tested below Θ. A temperature concentration diagram is drawn with the above mentioned experimental results.