It is of upmost importance to the food industry to design foods which efficiently deliver nutrients for the consumer’s well-being. However, this is an extraordinarily complex task which includes knowing the food’s composition, its structure at multiple length scales and the structure’s response to different environments. In order to understand food structure to this detail new techniques must be developed in order to gain a complete quantitative understanding.
In this study a collection of novel techniques have been used to quantify droplet interactions in different biological environments in order to determine the relationship between droplet interactions and destabilization mechanisms. Holographic optical tweezers were used to trap, visualise and measure the forces between droplets – without any mechanical contact. The optical tweezers were coupled with a stop-flow microfluidic device that provides the ability to control the aqueous environment and a series of experiments were carried out with the same pair of droplets in a multitude of environments. To determine the destabilisation mechanism the particle size distribution was measured over time using a combination of light scattering techniques and resistive pulse sensing which carries out droplet-by-droplet measurements to give a detailed understanding of the particle size distribution.1
Droplet-droplet interactions as small as pico-Newtons were experimentally measured as a function of electrolyte screening by exchanging the aqueous phase to increase the ionic strength. At the bulk level we probed environments including changes in pH, ionic strength and the presence of digestive enzymes. This is the first study to probe droplet interactions non-invasively with such precision, and represents a huge step towards understanding how emulsion droplets assemble in a bulk sample and define their macroscopic properties.
1 Somerville, J. A., Willmott, G. R., Eldridge, J., Griffiths, M., and McGrath, K. M.. Size and charge characterisation of a submicrometre oil-in-water emulsion using resistive pulse sensing with tunable pores. J. Colloid Interface Sci., Volume 394, p.243-251, (2013).
School of Chemical and Physical Sciences, Victoria University of Wellington, PO Box 600, Wellington, New Zealand;
Prof. Kathryn McGrath Kathryn.McGrath@vuw.ac.nz.
