Incorporating carbon nanotubes into highly concentrated emulsions: Possibilities & Challenges

Carbon nanotubes (CNTs) are an extremely valuable resource in nanotechnology, electronics, optics and other areas of material science. They are used as additives in order to improve the thermal, electrical, and mechanical properties of various structural materials like ceramics, metals and polymers.

However, the thermodynamic tendency of nanotubes to form 'agglomerates' and the difficulty of dispersing CNTs in highly viscous liquids are identified as key challenges.

Sharu B K, a researcher with the IITB-Monash Research Academy, is working on CNTs incorporated highly concentrated emulsions (HCEs), under the guidance of Prof Arup Bhattacharyya, Prof George Simon, and Prof Wenlong Cheng. Put simply, he plans to ascertain how CNTs can be effectively dispersed in HCEs and elucidate its influence on emulsion microstructure and flow properties.

The IITB-Monash Research Academy is a Joint Venture between IIT Bombay and Monash University, Australia. Opened in 2008, it operates a graduate research programme located in Mumbai that aims at enhancing research collaborations between Australia and India. Students study for a dually-badged PhD from both institutions, spending time during their research in both India and Australia.

Fig. 1: Schematic of single, double and multiwalled carbon nanotubes
(Courtesy: B.P.Grady: "Carbon nanotubes-Polymer Composites: Manufacture,
Properties and Applications", New Jersey, John Wiley and Sons Inc.,2011)

Multi-walled carbon nanotubes (MWNTs) consist of multiple rolled layers (concentric tubes) of graphene. Due to statistical probability and restrictions on the relative diameters of the individual tubes, the whole MWNT is usually a zero-gap metal. The preparation of functional CNTs-based nanocomposite or suspension necessitates the disentanglement of 'bundles' or 'aggregates' of CNTs. Researches have reported various approaches to de-bundle and disperse CNTs in different matrices and solvents.

Emulsions are colloidal dispersions consisting of two immiscible liquids. The dispersed liquid exists as droplets in a continuous liquid medium of another composition. The liquid that forms the droplets is referred to as the "dispersed phase", whereas the liquid which surrounds the dispersed droplets is referred to as the "continuous phase". In general, one of the liquid phases of emulsions is aqueous, while the other phase comprises of hydrocarbons and is referred to as oil.

Emulsions containing a dispersed phase volume fraction of higher than the maximum packing volume fraction of closely packed monodisperse spheres (~0.74) are referred to as HCEs. These emulsions have several applications—including the food industry, pharmaceuticals, cosmetics, petroleum products, and even in the mining industry as commercial explosives, explains Sharu.

As part of his experimental work, Sharu incorporated MWNTs into highly concentrated water-in-oil emulsions. Oil components form the continuous phase in water-in oil emulsions and Sharu is hoping that uniform dispersion of 'debundled' MWNTs in the oil phase of the emulsion could form a 3D network structure within the emulsion. The effective incorporation of MWNTs and its 'network-like' structure formation within the emulsion can be utilized to tune various properties of the emulsion.

To achieve the goal, it is necessary to selectively disperse and localize the MWNTs in the continuous phase of the emulsion. It is crucial that the MWNTs should stay at continuous phase of the emulsion and not move to the oil/water interface because this could lead to deterioration of emulsion stability.

Sharu synthesized two novel noncovalent modifier molecules and expects that these molecules could solubilize individual MWNTs in oil and restrict them in the oil phase. Furthermore, he is also studying how the incorporation of carbon nanotubes affects the structure and flow properties of the emulsions. The knowledge of flow properties of HCEs are extremely important to design and optimize the processing operations, pumping and packaging of the product.

Fig. 2: Highly concentrated emulsions: How does it look through optical and electron microscopes

The expected outcomes of Sharu's research project are:

  • Establishing fundamental understanding of methods for the dispersion CNTs in HCEs, and the role of noncovalent modifier molecules on this process.
  • Investigate the dispersion state of CNTs in HCEs and its influence on emulsion microstructure
  • Assessing the influence of CNTs in the flow characteristics of HCEs

Says Prof Murali Sastry, CEO, IITB-Monash Research Academy, "The Academy is a high-quality research institution that will grow talent, and contribute to solving important research challenges. It seeks to meet the future talent and research challenges of India and Australia by producing a steady supply of highly qualified skilled and trained PhD students; a need in the national innovation systems of both countries."

Sharu, we are confident, will soon join this elite group.

Research scholar: Sharu B K, IITB-Monash Research Academy

Project title: Investigation on morphology, rheology and thermal Conductivity of Carbon Nanotubes Incorporated highly concentrated emulsions

Supervisors: Prof Arup R Bhattacharyya, Prof George P Simon, Prof Wenlong Cheng, Dr Hans Zank

Contact details: bksharu@iitb.ac.in

This story was written by Mr Krishna Warrier based on inputs from the research student and IITB-Monash Research Academy. Copyright IITB-Monash Research Academy.