Assessment of the Dispersion Quality in Polymer Nanocomposites by Rheological Methods

Abstract

The properties of filled polymers and nanocomposites are strongly linked to the adequate dispersion of the solid phase into a polymeric matrix. However, obtaining the degree of dispersion within a polymer composite system is far from trivial. Typical methods for microstructural analysis such as electron and optical microscopy or scattering methods only investigate the local microstructure. In addition they are either labor intensive or may yield data that are difficult to analyze. Methods that focus more strongly on the end‐use properties, such as conductivity or bulk moduli, offer a global view of the material performance, but are of course post factum. The rheological properties of (nano)particle filled matrices in the molten state offer a cost‐effective alternative to evaluate the dispersion quality and can even be used during a production process. Moreover, it does not necessitate optical transparency, adequate scattering contrast, or conductivity. Typically, rheological data have been mainly used in qualitative terms and it is as yet unclear if the quality of dispersion can be quantified. The present work contains a systematic evaluation of methods to characterize the dispersion quality from rheology. Using a well‐defined model sample it is shown how the dispersion quality can be assessed quantitatively by studying the viscoelastic properties as a function of volume fraction. Moreover, a novel method is proposed, where the time evolution of the linear and nonlinear rheological properties at a fixed volume fraction is studied and analyzed. magnified image

Evolution of carbon nanotube dispersion in preparation of epoxy-based composites: From a masterbatch to a nanocomposite

“…This, together with a loss modulus (G&) remaining lower than G" all over the swept frequency range, indicates the presence of a network of entangled CNT clusters with a pseudo-solid-like behaviour. This situation is quite comparable to the cases where a solid-like gel network is emerged following an increase in the nanofiller content as observed in [21,30]. In contrast, the diluted 'N' resin system represents the typical hallmarks of a liquid-like material with a perfectly linear G&(!)…”

“…Furthermore, the storage modulus (G") of the resin system 'A' (solid circles) develops a plateau at low frequencies (!'0). A frequency independent rubbery plateau of G" is caused by highly interacting nanotubes, and is a well-known characteristic of a network or a structured entanglement in the suspending medium [21,30,31]. This, together with a loss modulus (G&) remaining lower than G" all over the swept frequency range, indicates the presence of a network of entangled CNT clusters with a pseudo-solid-like behaviour.…”

“…In the present work we take advantage of the accuracy and sensitivity of the rheological analysis to characterize the dispersion/ agglomeration state of CNTs. Characteristics of the microstructure and dispersion state of a suspension can be revealed by measuring the low and high frequency viscoelastic moduli [21,22]. Figure 4a presents linear viscoelastic storage and loss shear moduli of the diluted samples as a function of frequency.…”

“…However, microscopic techniques could not be efficiently employed at liquid state (especially in high concentration dispersions) and could merely provide a qualitative measure of the dispersion state over a small field of view. Indirect methods based on static or dynamic rheological analyses could efficiently be employed to obtain quantitative measures of the nanoparticle dispersion in liquid resins [4,[19][20][21][22]. This is mainly based on the fact that the dispersion quality of the nanoparticles often affects the viscosity and viscoelastic properties of liquid suspensions in different ways.…”

Dispersing hydrophilic nanoparticles in hydrophobic polymers: HDPE/ZnO nanocomposites by a novel template-based approach

“…A more conclusive insight on the state of dispersion of the filler can be obtained through rheological measurements. In particular, linear viscoelastic analysis is an extremely sensitive tool to probe the material structure over various length scales, offering an integrated picture of composite samples with higher reliability of the results compared to other methods, based on the analysis of the mechanical and barrier properties, which are too sensitive to micron-scale inhomogeneity [16]. The time evolution of G$ at % = 10 -1 rad/s and the frequency-dependent moduli of neat polymer and nanocomposites at different filler content are shown in Figure 4.…”