title: Making and breaking bridges in a Pickering emulsion.
abstract: OBJECTIVE
  Particle bridges form in Pickering emulsions when the oil-water interfacial area generated by an applied shear is greater than that which can be stabilised by the available particles and the particles have a slight preference for the continuous phase. They can subsequently be broken by low shear or by modifying the particle wettability.
  
  
  METHODS
  We have developed a model oil-in-water system for studying particle bridging in Pickering emulsions stabilised by fluorescent Stöber silica. A mixture of dodecane and isopropyl myristate was used as the oil phase. We have used light scattering and microscopy to study the degree to which emulsions are bridged, and how this is affected by parameters including particle volume fraction, particle wettability and shear rate. We have looked for direct evidence of droplets sharing particles using freeze fracture scanning electron microscopy.
  
  
  RESULTS
  We have created strongly aggregating Pickering emulsions using our model system. This aggregating state can be accessed by varying several different parameters, including particle wettability and particle volume fraction. Particles with a slight preference for the continuous phase are required for bridging to occur, and the degree of bridging increases with increasing shear rate but decreases with increasing particle volume fraction. Particle bridges can subsequently be removed by applying low shear or by modifying the particle wettability.
authors.affiliation: School of Physics & Astronomy, The University of Edinburgh, Peter Guthrie Tait Road, Edinburgh EH9 3FD, UK. Electronic address: David.French@ed.ac.uk.
authors.forename: David J
authors.initials: DJ
authors.lastname: French
authors.affiliation: Formulation Technology Group, Syngenta Crop Sciences, Jealott's Hill International Research Centre, UK.
authors.forename: Phil
authors.initials: P
authors.lastname: Taylor
authors.affiliation: Syngenta Inc., 410 Swing Rd, P.O. Box 183000, Greensboro, NC 27419-8300, USA.
authors.forename: Jeff
authors.initials: J
authors.lastname: Fowler
authors.affiliation: School of Physics & Astronomy, The University of Edinburgh, Peter Guthrie Tait Road, Edinburgh EH9 3FD, UK.
authors.forename: Paul S
authors.initials: PS
authors.lastname: Clegg
keywords: Aggregating droplets; Aggregating emulsion; Droplet adhesion; Particle bridging; Particle-stabilized emulsions; Pickering emulsions; Process conditions; Shear history