Florent Dalmas

Tuning the mechanical properties in model nanocomposites: Influence of the polymer‐filler interfacial interactions

This paper presents a study of the polymer-filler interfacial effects on filler dispersion and mechanical reinforcement in Polystyrene (PS) / silica nanocomposites by direct comparison of two model systems: un-grafted and PS-grafted silica dispersed in PS matrix. The structure of nanoparticles has been investigated by combining Small Angle Neutron Scattering (SANS) measurements and Transmission Electronic Microscopic (TEM) images. The mechanical properties were studied over a wide range of deformation by plate/plate rheology and uni-axial stretching. At low silica volume fraction, the particles arrange, for both systems, in small finite size non-connected aggregates and the materials exhibit a solid-like behavior independent of the local polymer/fillers interactions suggesting that reinforcement is dominated by additional long range effects. At high silica volume fraction, a continuous connected network is created leading to a fast increase of reinforcement whose amplitude is then directly dependent on the strength of the local particle/particle interactions and lower with grafting likely due to deformation of grafted polymer.

Low dipolar interactions in dense aggregates of aligned magnetic nanowires

Magnetic interactions in aggregates of polyol-synthesized cobalt nanowires are studied by δM plots. Negative δM values are obtained as expected for magnetostatic coupling between physically isolated nanowires, without exchange interactions. Very weak interactions (down to δM = −0.05) are achieved by alignment and dispersion into polymeric matrices. We attribute this to the fact that during the fabrication of the composite materials, the nanowires reorganize so as to minimize the dipolar interactions. Since the δM-plots are sensitive to the nature of the demagnetized state, it is shown by micromagnetic simulations that the ac demagnetized state provides the best choice of a starting point since it ensures that macroscopic configurations consisting of single domain states of each wire are compared. The low interactions observed in these materials suggest that these composite materials are candidates for rare-earth free permanent magnets since demagnetization phenomena are minimized.