Effect of Incorporation of Multiwalled Carbon Nanotubes on the Microstructure and Flow Behavior of Highly Concentrated Emulsions

Abstract

Multiwalled carbon nanotubes (MWCNTs) were incorporated into highly concentrated water-in-oil emulsions with the ultimate aim of achieving a uniform and effective dispersion of MWCNTs within the emulsion matrix. The emulsion was formulated in such a way, wherein the internal phase consists of higher than 90 wt %. By keeping the same aqueous-to-oil phase ratio, the amount of MWCNTs in the oil phase was systematically adjusted to investigate their effects on the microstructure development and rheological behavior of the emulsion. The addition of MWCNTs led to a reduced droplet size and also resulted in a narrower distribution of the droplet size. The rheological behavior of nanotube-incorporated emulsions was characterized with varying MWCNT concentrations and also as a function of the emulsification time. The rheological characteristics of the nanotube-incorporated emulsions were identical to those of the neat emulsion and were primarily governed by the variation in the droplet size and droplet-size distribution. However, the yield strain and cross-over strain were independent of the mean droplet size and polydispersity of the emulsion. Emulsions that have smaller droplets exhibited higher storage modulus ( G ′), yield stress (τ Y ), and apparent viscosity (η). For all refining times investigated, nanotube-incorporated emulsions have higher G ′, τ Y , and η values when compared to the neat emulsion, and these values further increased with the MWCNT concentration. This was primarily due to the decrease in the droplet size with MWCNT addition. Furthermore, our findings suggest that the incorporated MWCNTs did not induce any significant change in the rheological behavior of emulsions with identical droplet sizes, and it remained essentially unchanged with the concentration of MWCNTs. However, the nanotube-incorporated emulsions possessed solidlike behavior up to a higher applied stress when compared to a neat emulsion of identical droplet size.

Basic Principles of Emulsion Templating and Its Use as an Emerging Manufacturing Method of Tissue Engineering Scaffolds

“…HIPEs are viscous emulsions, and they have a mayonnaise-like consistency with yellowish-white colour due to the difference in light refraction between the oil and water phases. They exhibit shear-thinning behaviour (Sears et al, 2016;Bhagavathi Kandy et al, 2018;Aldemir Dikici et al, 2020). The viscosity of HIPEs depends on the viscosities of the internal and continuous phases, droplet size, and the internal phase volume (Ford and Furmidge, 1967;Das et al, 1992;Borwankar and Case, 1997;Welch et al, 2006;Ilia Anisa and Nour, 2010).…”

Effect of Organic Modification on Multiwalled Carbon Nanotube Dispersions in Highly Concentrated Emulsions

“…However, developing a homogeneous dispersion involving “individualized” MWCNTs in the oil blend (which forms the continuous phase of the HCE) remains a difficult task. It was noticed earlier that a fraction of MWCNTs remained in the agglomerated-state in the emulsion matrix . Moreover, the fraction of remaining MWCNT agglomerates increased with the increase in MWCNT concentration in the HCE.…”

“…Further details of the PIBSA-derivative emulsifier can be found elsewhere. 16 The constituents of the aqueous phase, such as ammonium sulfate, ammonium chloride, and other trace additives, were procured from Sigma-Aldrich. Deionized water was used to prepare the aqueous phase, and the trace additives were added to adjust the pH of the salt solution.…”

“…Several studies were reported on HCEs incorporating nanoparticles, including multiwalled carbon nanotubes (MWCNTs), either as Pickering stabilizers or co-stabilizers. 12−16 CNTs with various surface functionalities were incorporated into HCEs to prepare conductive polyHIPE foams with a low electrical percolation threshold. 17−21 A significant level of understanding about the formation of electrically percolating MWCNT networks in HCEs has been gained from these studies on polyHIPE composite foams.…”

“…Carbon nanotubes (CNTs) are being widely used to improve the thermal, electrical, and mechanical properties of a variety of materials, including ceramics, metals, and polymers. Several studies were reported on HCEs incorporating nanoparticles, including multiwalled carbon nanotubes (MWCNTs), either as Pickering stabilizers or co-stabilizers. − CNTs with various surface functionalities were incorporated into HCEs to prepare conductive polyHIPE foams with a low electrical percolation threshold. − A significant level of understanding about the formation of electrically percolating MWCNT networks in HCEs has been gained from these studies on polyHIPE composite foams. Kim et al have reported a percolation threshold of less than 1 wt % in polyHIPE foams …”