What are the rheological properties of graphene polymers?

What are the rheological properties of graphene polymers?

It has been observed that the degree to which graphene is dispersed in the polymer matrix can affect the flow or rheological properties of polymer composites. As a result, the most important properties of the nanoscale materials are sensitive to the spreading quality. This article aims to highlight the importance of rheological analysis in graphene polymer research.

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The role of graphene in polymer composite

Polymer-based nanocomposites have attracted a significant amount of research attention in recent decades. This is because a very minimal nanofiller enables improved properties compared to their corresponding unfilled counterparts, creating new perspectives for the ongoing demand for advanced polymer composites. In this context, a wide range of nanofillers such as ceramics, metals and carbon-based fillers have been embedded in a polymer matrix to produce high performance materials that can continuously expand polymer markets.

Graphene nanofillers have shown great potential for the framework of new polymer-based nanocomposites due to their low density, exceptional mechanical, electronic properties and high thermal conductivity.

However, the potential of graphene to provide improved properties when loaded into polymers is strongly dependent on its dispersion state in the host matrix; in fact, graphene tends to aggregate when immersed in a viscous medium, and this situation limits the full realization of their theoretically inherent advantages.

Rheological analysis and its significance in graphene / polymer research

A very effective tool for monitoring the state of dispersion of graphene in a polymeric matrix is ​​the evaluation of its rheological properties, such as viscosity and viscoelastic properties. The graphene dispersion state and the degree of polymer-graphene interaction significantly affect the viscoelastic properties of polymer nanocomposites. As a result, the concentration of graphene significantly affects the continuous graphene network throughout the host polymer.

The resulting polymer network becomes increasingly interconnected as the amount of graphene increases. It eventually reaches a critical concentration, known as the rheological percolation threshold, at which a mechanically efficient network is formed between the graphene and the polymer. The concentration and distribution of the graphene filler determine this point.

The rheological behavior of the graphene dispersed in a polymer matrix can generally be divided into three states. At low nanofill load, the incorporation of the graph results in only short-distance interactions; this is known as the dilution regime. The emergence of a percolation network occurs when the nanofill content increases, resulting in a shift from the diluted to the semi-diluted state; in this state, the rheological behavior of the nanocomposite is dependent on the interactions between filler and polymer.

When the graphene content exceeds the percolation threshold, the concentrated state is reached, and the rheological functions approach asymptotic values, with extremely high viscosity and dynamic modulus.

In fact, the rheological behavior of graphene / polymer-based systems reveals basic information about the graphene / polymer interactions established at the interface, as well as further insight into the possible arrangement of graphene-based nanofillers in the polymer host matrix.

Research examples of rheological properties of graphene polymer materials

By using nanofillers with improved dispersion or high aspect ratios, the percolation transition can be achieved at dilute concentrations. In the case of carbon black (CB) -containing polymer composites, for example, the amount of CB required to form a percolating path through the matrix is ​​typically about 10% by weight. percent, but this amount is dramatically reduced to 0.2 weight percent. percent by using graphene-like fillers.

Researchers discovered that the addition of graphene to biodegradable polymers such as polylactic acid can significantly increase the viscosity and dynamic modulus, resulting in increased strength and durability of biodegradable plastics. As a result, the rheological analysis provides a basic understanding of the machining properties of the nanocomposites.

Equipment used in rheological analysis

Rheometers are used to evaluate the rheological properties of molten polymers as shear rates and temperatures vary. Viscosity rheology tests are performed while the polymer is in the melt phase or after it has been dissolved in a solvent.

Thermo fisher ScientificTM is an example of a supplier of a rheometer. Specifically, their HAAKE rheometers are widely recognized for accuracy and ease of use. The instruments are designed to reliably measure the mechanical properties and viscosity properties of polymers in different states.

A comprehensive rheological characterization of polymeric materials can be achieved by applying a variety of test methods. Frequency sweep data provide a direct measure of the viscous and elastic properties of a polymer. These are represented by the storage and the loss modules (G ‘& G’ ‘) measured at different frequencies / time scales. Rotary rheometers can also be used to perform Dynamic Mechanical Thermal Analysis (DMTA), where the data obtained are used to identify characteristic phase transitions from a liquid-like to a solid.

Summary

Evaluating rheological behavior is a very powerful tool for determining the dispersion of graphene nanofillers and their interactions between polymer chains, as it strongly affects the viscoelastic properties of the material. In addition, rheological properties are critical when analyzing the melt flow properties of graphene / polymer nanocomposites. The understanding and design of flow behavior is crucial to its processing and commercial applications.

Definition of nanorheology: techniques and applications.

References and further reading

Das, M. and Dey, A. (2022). Rheological properties of polymer-graphene composites. Polymer nanocomposites containing graphene, 183-210 https://www.sciencedirect.com/science/article/pii/B9780128216392000215

C. Küchenmeister-Lehrheuser, K. Oldörp, F. Meyer, Clamping tool for Dynamic Mechanical Analysis (DMTA) with HAAKE MARS rheometers, Thermo Fisher Scientific Product Information P004 (2016)

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