Universal features of the melt elasticity of interacting polymer nanocomposites

Reconsideration of the Rheology of Silica Filled Natural Rubber Compounds

There is substantial progress along with giant debate in reinforcement mechanisms in relation to structured filler network and heterogeneously retarded polymer dynamics, while the dissipation behaviors have never been clarified for nanoparticle filled polymers. Herein dynamic rheological behaviors of silica filled natural rubber were investigated. Master curves of linear rheology in the hydrodynamic regime and those of the nonlinear Payne effect at a predetermined frequency were created, disclosing a leading role of dynamically retarded bulk rubbery phase to the hydrodynamic regime and a leading role of molecular disentanglement in the bulk phase to the Payne effect. The methodology is able to account for both reinforcement and dissipation of the compounds as a function of filler content. Furthermore, a frequency-dependent hydrodynamic to non-hydrodynamic transition is revealed, revealing the importance of the relaxation of chains in the bulk phase to both reinforcement and dissipation of the compounds. It is suggested that the dynamics of the bulk phase play a critical role for the rheology in the hydrodynamic regime while the fractal filler aggregates become dominative only in the terminal non-hydrodynamic regime where the bulk phase relaxes sufficiently.

Revealing nanocomposite filler structures by swelling and small-angle X-ray scattering

Polymer nanocomposites are used widely, mainly for the industrial application of car tyres. The rheological behavior of such nanocomposites depends in a crucial way on the dispersion of the hard filler particles – typically silica nanoparticles embedded in a soft polymer matrix. It is thus important to assess the filler structure, which may be quite difficult for aggregates of nanoparticles of high polydispersity, and with strong interactions at high loading. This has been achieved recently using a coupled TEM/SAXS structural model describing the filler microstructure of simplified industrial nanocomposites with grafted or ungrafted silica of high structural disorder. Here, we present an original method capable of reducing inter-aggregate interactions by swelling of nanocomposites, diluting the filler to low-volume fractions. Note that this is impossible to reach by solid mixing due to the large differences in viscoelasticity between the composite and the pure polymer. By combining matrix crosslinking, swelling in a good monomer solvent, and post-polymerization of these monomers, it is shown that it is possible to separate the filler into small aggregates. The latter have then been characterized by electron microscopy and small-angle X-ray scattering, confirming the conclusions of the above mentioned TEM-SAXS structural model applied directly to the highly loaded cases.

New insights into the elasticity and multi-level relaxation of filler network with studies on the rheology of isotactic polypropylene/carbon black nanocomposite

The elasticity and multi-level relaxation behavior of filler network in isotactic polypropylene/carbon black nanocomposites were systematically studied, which was instructive for the development and application of viscoelastic materials.

Mechanism of aggregate formation in simplified industrial silica styrene-butadiene nanocomposites: effect of chain mass and grafting on rheology and structure

The formation of aggregates in simplified industrial styrene-butadiene nanocomposites with silica filler has been studied using a recent model based on a combination of electron microscopy, computer simulations, and small-angle X-ray scattering. The influence of the chain mass (40 to 280 kg mol(-1), PI < 1.1), which sets the linear rheology of the samples, was investigated for a low (9.5 vol%) and high (19 vol%) silica volume fraction. 50% of the chains bear a single graftable end-group, and it is shown that the (chain-mass dependent) grafting density is the structure-determining parameter. A model unifying all available data on this system is proposed and used to determine a critical aggregate grafting density. The latter is found to be closely related to the mushroom-to-brush transition of the grafted layer. To our best knowledge, this is the first comprehensive evidence for the control of the complex nanoparticle aggregate structure in nanocomposites of industrial relevance by the physical parameters of the grafted layer.

Network evolutions in both pure and silica-filled natural rubbers during cyclic shear loading

During the fatigue process, the loose silica agglomerates are disrupted and then the closed ones can also be gradually broken down, and the filler particles become more and more homogeneous.

Computational study of nanoparticle dispersion and spatial distribution in polymer matrix under oscillatory shear flow

In this work, nonequilibrium molecular dynamics simulations were performed to investigate the dispersion and spatial distribution of spherical nanoparticles (NPs) in polymer matrix under oscillatory shear flow. We systematically analyzed the influences of four important factors that consist of NP-polymer interfacial strength, volume fraction of NPs, shear conditions, and polymer chain length. The simulation results showed that the oscillatory shear can greatly improve the dispersion of NPs, especially for the polymer nanocomposites (PNCs) with high NP-polymer interfacial strength. Under specific shear conditions, the NPs can exhibit three different spatial distribution states with increasing the NP-polymer interfacial strength. Interestingly, at high interfacial strength, we observed that the NPs can be distributed on several layers in the polymer matrix, forming the PNCs with sandwich-like structures. Such well-ordered nanocomposites can exhibit a higher tensile strength than those with the NPs dispersed randomly. It may be expected that the information derived in present study provides a useful foundation for guiding the design and preparation of high-performance PNCs.