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SUMMARY:Colloids and coatings for colours - Dr Andrew M. Howe\, Kodak Euro
 pean Research\, Cambridge
DTSTART:20060505T100000Z
DTEND:20060505T110000Z
UID:TALK4954@talks.cam.ac.uk
CONTACT:Dr C. P.  Caulfield
DESCRIPTION:For over a century\, sub-micron colloidal particles\, now ofte
 n referred to as nanoparticles\, have been formulated into water-based sus
 pensions and then coated and dried for use as a medium to preserve and dis
 play images.  For the majority of that time\, the dominant technology for 
 both capture and display of images was silver halide photography.  Followi
 ng the recent rise of digital photography\, image generation by inkjet and
  thermal dye transfer printing have become increasingly popular.  This pre
 sentation will describe some ways in which colloid and interface science h
 as contributed to both silver halide and inkjet coatings.  \nSilver halide
  crystals and liquid-crystalline dye assemblies capture light\, while the 
 colours are produced by interfacial reaction of developer organic molecule
 s that have been coated as an oil-in-water emulsion.  Naturally\, the role
 s of surfactants in emulsion formation and coating control are crucial.  P
 olymers too have many functions\, providing colloidal stabilisation\, rheo
 logy control\, physical and chemical gelation\, and a reversibly swellable
  medium that protects the image.\nIn contrast\, the colours in inkjet prin
 ting are not created from the coated layer but are delivered separately in
  the form of liquid microdroplets.  Here\, one of the major role of colloi
 dal particles is to provide a quick-drying layer that gives sharp\, glossy
  images.  The processing of colloidal materials that are well suited to gi
 ve glossy\, porous layers can be challenging\, as illustrated by the extre
 mely unusual behaviour exhibited by a commercially available boehmite.  Th
 is material disperses readily in water to give aggregates of\, apparently 
 inter-grown\, crystallites.  The dispersions are colloidally stable at low
  pH (optimally\, 2  4)\, where they have a strong surface charge.  However
 \, concentrated suspensions of this material undergo irreversible shear-th
 ickening and subsequent reversible switching between jammed and high-visco
 sity states.\n
LOCATION:Open Plan Area\, BP Institute\, Madingley Rise CB3 0EZ
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