THE ZERO AVERAGE CONTRAST CONDITION - THEORETICAL PREDICTIONS AND EXPERIMENTAL EXAMPLES

This paper deals with mixtures of homopolymers and copolymers in solve nts under the zero average contrast condition. This condition is chose n in order to decouple the correlations due to polymer composition flu ctuations from those due to polymer concentration fluctuations. This m akes the measurement of these correlations much easier using technique s based on static light scattering, photoncorrelation spectroscopy, sm all angle neutron scattering, neutron spin echo or X-ray scattering. I n the first part of the paper, a simple theoretical framework is devel oped to present the guidelines for the interpretation of the scatterin g data. In the second part, some experimental examples are discussed u sing the scattering techniques mentioned above. Data obtained from var ious systems involving alike (deuterated and ordinary) homopolymers an d diblock copolymers as well as unalike species are considered. An exa mple of mixtures of polyelectrolytes in aqueous solutions is also disc ussed within the framework of the zero average contrast condition. (C) 1997 Elsevier Science Ltd.