Polymer-Grafted-Nanoparticles Nanocomposites: Dispersion, Grafted Chain Conformation, and Rheological Behavior

Abstract

International audienceWe investigate the dispersion mechanisms of nanocomposites made of well-defined polymer (polystyrene, PS) grafted-nanoparticles (silica) mixed with free chains of the same polymer using a combination of scattering (SAXS/USAXS) and imaging (TEM) techniques. We show that the relevant parameter of the dispersion, the grafted/free chains mass ratio R tuned with specific synthesis process, enables to manage the arrangement of the grafted nanoparticles inside the matrix either as large and compact aggregates (R \textless 0.24) or as individual nanoparticles dispersion (R \textgreater 0.24). From the analysis of the interparticles structure factor, we can extract the thickness of the spherical corona of grafted brushes and correlate it with the dispersion: aggregation of the particles is associated with a significant collapse of the grafted chains, in agreement with the theoretical models describing the free energy as a combination of a mixing entropy term between the free and the grafted chains and an elastic term of deformation of the grafted brushes. At fixed grafting density, the individual dispersion of particles below the theoretical limit of R = 1 can be observed, due to interdiffusion between the grafted and the free chains but also to processing kinetics effects, surface curvature and chains poly dispersity. Mechanical analysis of nanocomposites show the appearance of a longer relaxation time at low frequencies, more pronounced in the aggregated case even without direct connectivity between the aggregates. Correlation between the local structure and the rheological behavior suggests that the macroscopic elastic modulus of the nanocomposite could be described mainly by a short-range contribution, at the scale of the interactions between grafted particles, without significant effect of larger scale organizations

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

“…For the un-grafted system, this process would be provided by a "glassy layer" surrounding the filler [6,21,37], while for the grafted system it is given by contact between grafted layers [16,17,19,38]. These grafted layers could also be glassy, as mobility of grafted chains in the interface could be reduced [18].…”

“…These grafted layers could also be glassy, as mobility of grafted chains in the interface could be reduced [18]. In this view, the morphology of the aggregates (a dispersion of individual particles does not give comparable solidlike effect amplitudes [16,17,18]) is also supposed to play a role especially in the quantity of polymer chains involved [39]. However, our results show that a strong modification of the polymer-filler interface with grafting (associated with a small modification of the aggregates morphology) does not influence the solid-like response of the materials.…”

Interfacial relaxation mechanisms in polymer nanocomposites through the rheological study on polymer/grafted nanoparticles

“…By using the transmission electron tomography (TEMT) technology, Dalmas et al find that either densely packed or isolated NPs could be obtained by changing the ratio of the grafted chains and matrix chains [17]. It is obvious that the dispersion state of the NPs could be controlled by the surface decoration, either by grafting with silane molecules [18] or the matrix-like polymer chains [19], or other simple approach to prepare the hybrid organic/inorganic particles in-situ [20e22]; after the NPs are surface modified, especially grafted with polymer chains, the polymer-filler interfaces have also been grandly changed [23,24]. Therefore, the investigation about the effect of the topology of the grafted NPs on the properties of PNC is interesting and necessary.…”

POSS Grafting on Polyethylene and Maleic Anhydride‐Grafted Polyethylene by One‐Step Reactive Melt Mixing

“…Recently, grafting of POSS into the polymeric matrix by reactive processing, that is a solvent-free method for the chemical modification of existing polymers, has been thought as an advisable solution to solve issues related to the nanofillers' incorporation into polymer systems, maintaining ease of processing, versatility, and costeffectiveness. [18][19][20] In particular, the dispersion of the nanoparticles in the polymeric matrix as well as polymer/nanofiller interactions is expected to be improved by the use of POSS molecules bearing functional groups that can interact with reactive groups grafted on the polymeric backbone during a one-step melt blending 21,22 or introducing reactive groups onto the POSS molecules that can be properly activated during processing to attach them in the polyolefin chains. 23 Therefore, inorganic POSS molecules containing a reactive monofunctionality may be the ideal nanofiller for use in the construction of organic-inorganic hybrid nanomaterials by one-step reactive melt mixing.…”