Caractérisation des Propriétés Structurales des Polymères par Diffusion de Neutrons aux Petits Angles.

Abstract

Characterizing the properties of macromolecules in solution is one of the fundamental means to assess the relationship between structural parameters and conformation, which in turn controls properties ranging from self-assembly to rheology. Small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS) are the reference methods for performing this characterization. On the other hand, the use of theoretical models helps researchers interpret their scattering data by allowing them to identify the physicochemical parameters of the studied polymeric system. Indeed, based on the random phase approximation (RPA), we have studied the structural behavior of solutions of branched polymers, binary blends of branched polymers, and ternary blends consisting of two chemically different branched polymers immersed in a good solvent. For this study, we considered linear polymers, cyclic polymers, star-branched polymers formed by f linear branches, as well as f branches of cyclic shape. Initially, we expressed their form factors and plotted their angular dependence for different values of the Flory exponent, ν. The curves obtained revealed a structural behavior that varied depending on the polymer architecture. Additionally, we determined the power laws for the different polymers in various regions of the wave vector Q. Next, we expressed and represented the angular variations of the structure factors for the aforementioned polymeric systems for different values of the branch number f. Through this study, we demonstrated that the scattering intensity is a monotonically decreasing function of the wave vector Q. At the thermodynamic limit corresponding to Q=0, it remains finite, implying a tendency towards macrophase separation in the studied systems and an asymptotic form at large Q values. Furthermore, the diffusion behavior of the aforementioned systems was compared to that of their linear and cyclic counterparts. The analysis of the different curves revealed that the scattering intensity of star-branched polymers is higher than that of cyclic and linear polymers due to the reduction in entanglements, the large number of chain ends, and the more compact architecture.