Incorporation of nanoparticles in the formulation of new products

Paul Boughton

Incorporation of nanoparticles into the formulation of high tech and everyday products is becoming increasingly prevalent with an expected exponential growth as new sectors adopt this technology. Dr Gul Ozcan-Taskin reports.

The UK’s Royal Society of Chemistry cited healthcare, energy, security, electronics and computing as notable areas for nanotechnology development, for example, targetted drug and gene therapy, solar cells using nanotechnology, nano barcoding, carbon nanotube electronic components.  

The process engineering challenge and objective, in terms of the manufacture of products with nanoparticles in their formulation, is to obtain a final product which is highly dispersed, functional and stable with defined properties and one that can be achieved in sufficiently large quantities to take this product to market. This is one of the areas that BHR Group has been active in, working closely with industry, enhancing and diversifying the application of current expertise and knowledge to wider industrial segments.[Page Break]
BHR Group is an independent industrial research and technology organisation specialising in the application of fluid engineering to nanotechnology and other industrial sectors. Established for over 65 years, BHR Group helps international companies maintain their competitive edge by providing independent and impartial expert advice, specialising in technical services and knowledge transfer.
One of the ways to achieve this has been through industrial research consortia. DOMINO, established in 2007, is a recently established consortium and investigates the dispersion of nanoparticles, microparticles and nanoclays in liquids.  Like other consortia at BHR Group, it is solely sponsored by a club of industrial companies ranging from end-users from different industrial segments to equipment manufacturers. The research programme, steered by the members, is undertaken at BHR Group and comprises both experimental studies and numerical modelling. The objective of the DOMINO project is to enable its member companies to increase the profitability of their processes involving the dispersion of nano and microparticles in liquids based on the findings from this programme.
Typically, feed materials are put in contact using an incorporation device and thus a pre-dispersion is prepared.  This is then passed through a more energy intensive device to achieve a fine dispersion with stable and desired product properties.[Page Break]
The process studied consists of different steps as schematically shown in Fig. 1.
However, the behaviour of dry nanoparticle powders in fluid can take various paths, but typically attractive forces cause these primary particles to clump together to form aggregates, which in turn can form agglomerates.
The final dispersion stage is therefore needed to de-agglomerate the nanoparticles back to a suspension unclogged by relatively large agglomerates. For the manufacturer there are at least five equipment options or combinations of equipment for the final dispersion device (valve homogeniser, rotor-stator, the popular stirred bead mill, etc). Each has its own pros and cons in terms of effectiveness, energy usage, operating time and capital cost (Fig 2).[Page Break]
Using specialist equipment, DOMINO is able to assess the nanoparticle suspension and the degree of agglomeration pre- and post-final dispersion.
Results would typically resemble Fig. 3 with the crucial 1 micron cut-off point between coarse particle clumps and the desired sub-micron particles.  As the suspension is processed by the final device(s) the number and average size of coarse agglomerates decreases, whereas the number of “fines” increases.
DOMINO has been working on these processes to prepare design procedures and recommendations relevant to industrial applications.  In parallel to the experimental programme, numerical modelling is performed to provide a better insight in terms of the flow through various process devices and also to develop a predictive tool for the deagglomeration process. Fig. 4 gives an overview of the scope of work undertaken within DOMINO. The evolution of particle size distribution, dispersion rheology, and morphology of nanoparticle clusters provide information in terms of the mechanisms and kinetics of break up or delamination with different process devices and under different operating conditions. These are complemented with information obtained from numerical modelling and recommendations for design and equipment selection.
This collaborative model practiced within BHR Group for decades has allowed research findings find their way quickly to industrial practice rather than being confined to reports and other publications.

Dr Gul Ozcan-Taskin is with VirtualPiE Ltd (trading as BHR Group) The Fluid Engineering Centre Cranfield, Bedfordshire, UK.
Reference: Özcan-Taskin, N. G., et al., Effect of particle type on the mechanisms of break up of nanoscale particle clusters, Chem Eng Res Des (2009), doi:10.1016/j.cherd.2008.12.012

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