Neutron scattering from a series of compatible polymer blends: Significance of the Flory χF parameter

Abstract

In polymer blends the Flory χ F parameter, describing the short range interactions between chain segments, is frequently represented by a structureless point‐like interaction. However, in the mean field approximation, the influence of this parameter is directly enhanced by the degree of polymerization of the chains. This large enhancement is also effective with regard to the short range spatialstructure of χ F (r) and makes it possible to detect these structural details from a small angle neutron scattering experiment. We present a new way of representing the neutron data so as to explicitly determine these details and we demonstrate the method for the system polytetramethyl carbonate/deuterated polystyrene. The temperature dependence displayed by this system appears to be anomalous within the mean field approximation. However, we show that it can be successfully interpreted in terms of a structural model for χ F (r) which consists of spatially separated positive and negative contributions within a 1–10 Å range. This form is supported by examining the relation of χ F to the pseudopotential interactions between the segments. In the experimental part of this work we also compare our model with SANS data from two other systems (a) polyvinylmethyl ether/deuterated polystyrene, and (b) polyparamethyl styrene/deuterated polystyrene. The last two show a ‘‘normal’’ behavior and are consistent with a relatively structureless χ F parameter.