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SUMMARY:A TEM and SAXS/USAXS study of particle growth of a mesoporous sili
 ca - Viveka Alfredsson\, Lund University\, Sweden
DTSTART:20080512T140000Z
DTEND:20080512T150000Z
UID:TALK11052@talks.cam.ac.uk
CONTACT:Dr Jonathan Barnard
DESCRIPTION:Mesoporous silica particles SBA-15 (p6mm) have been studied wi
 th TEM and the growth has been followed by in-situ small x-ray angle scatt
 ering (SAXS) and ultrasmall angle x-ray scattering (USAXS). A difference i
 n synthesis temperature of only 5 degrees dramatically changes the morphol
 ogy of the mesoporous silica particles. The shape of the particles suggest
 s a difference in growth mechanism between these two temperatures. In our 
 previous work\, we concluded that the embryonic particle is a floc consist
 ing of micelles of the structure-directing amphiphilic polymer in a matrix
  of silica. With time\, as silica condenses\, the micelles rearrange and e
 ventually the ordered\, in this case p6mm\, structure is generated. Based 
 on the particulate shape at the lower synthesis temperature\, a model is p
 roposed to explain the growth behaviour. Once the flocs have started to or
 ganise into the ordered phase they will go through a second aggregation st
 ep with seven smaller particles/flocs joining into one larger. This appear
 s to be an oriented aggregation with crystallographic equivalent faces joi
 ning. Due to the liquid nature of the material at this point of the synthe
 sis the joining interface will almost “heal” forming a more or less pe
 rfect structure. However there is some reminiscence of the primary particl
 es. The electron micrographs show particles with holes within and low cont
 rast at the interface where the particles have joined. If the synthesis is
  performed at the higher temperature this oriented aggregation step does n
 ot occur and the particles have a very different morphology. The combined 
 SAXS and USAXS measurements provide information regarding micellar evoluti
 on\, formation of the ordered structure and formation of larger particles.
  
LOCATION:T001 [Tower Seminar Room]\, Materials Science and Metallurgy\, De
 partment of
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