The good dispersion of nano-fillers within a polymer and strong interfacial bonding are two key factors that can increase the viscosity of a nanocomposite.

1. Good dispersion of nano-fillers: Nano-fillers are typically solid particles with nanoscale dimensions that are dispersed within the polymer matrix. When these nano-fillers are well-dispersed throughout the polymer, it means that they are evenly distributed and separated from each other at the nanoscale level. This dispersion has a significant impact on the viscosity of the nanocomposite due to the following reasons:

a. Hindered molecular movement: The presence of dispersed nano-fillers creates barriers that hinder the movement of polymer chains. The polymer chains have to navigate around or through the nano-fillers, which increases the resistance to flow and results in higher viscosity.

b. Enhanced chain entanglement: The nano-fillers can act as physical obstructions, causing the polymer chains to entangle more effectively. As a result, the polymer chains become more interlocked, further increasing the viscosity of the nanocomposite.

c. Reduction of free volume: The presence of nano-fillers reduces the available free volume within the polymer matrix. Free volume refers to the space between polymer chains, which allows them to move more freely. By reducing the free volume, the mobility of polymer chains is restricted, leading to higher viscosity.

2. Strong interfacial bonding: The interfacial bonding refers to the interaction between the nano-fillers and the polymer matrix. A strong interfacial bonding between the nano-fillers and the polymer matrix is essential for creating a structurally robust nanocomposite. The strong interfacial bonding can impact viscosity in the following ways:

a. Load transfer efficiency: When there is a strong bond between the nano-fillers and the polymer matrix, stress can be efficiently transferred from the polymer to the nano-fillers during flow or deformation. This load transfer mechanism increases the resistance to flow and results in higher viscosity.

b. Reduced segmental mobility: A strong interfacial bonding can restrict the segmental mobility of polymer chains near the filler-polymer interface. This restricted mobility contributes to a higher viscosity since the polymer chains are less able to move past each other easily.

Overall, the good dispersion of nano-fillers and strong interfacial bonding in a nanocomposite lead to increased resistance to flow and reduced mobility of the polymer chains, resulting in higher viscosity compared to the pure polymer matrix. These properties can have significant implications for the mechanical, thermal, and rheological behavior of the nanocomposite material.

Hi,

it depends on whether you mean nanocomposite melts or solution.

Haresh Bhanushali is right regarding the melts. The reduced mobility has two categories - an almost completely immobilized layer around the particles (about 1-3 nm) thick and a much wider (several tens of nm) frustrated layer with only partially reduced mobility. Considering aggregates and clusters as one big particle, the universal scaling parameter is the surface area over the average interparticle distance. The "good dispersion" is characterized by a higher number of smaller species found around the matter. Therefore, it has a high surface area and a small interparticle distance, causing the highest increase in viscosity. See Figure 2 in our paper:

Article Effect of Nanoparticle Organization on Molecular Mobility an...

The fundamental explanation of this effect is found in nanoconfinement.

Article Nature of dynamic gradients, glass formation, and collective...

The viscosity increase in solutions is caused by the enlarged hydrodynamic volume caused by adsorbed polymer layer. In some specific cases, it may also decrease the viscosity due to depletion attraction.

Article Bulk Polymer Nanocomposites with Preparation Protocol Govern...

Either way, the strength of particle-polymer interaction is crucial.

Thank you very much Haresh Bhanushali and Petr Lepcio for the valuable answers and information provided. That's greatly appreciated!