In Chem. Commun., 2012, 48, 1860-1862, Dionysios D. Dionysiou with colleagues report an attractive approach to size control of titania aggregates prepared by alkoxide sol-gel. They have used ionic strength in salt solutions to control surface charge of the particles and demonstrated possibility to isolate well defined fractions exploiting this approach.
http://pubs.rsc.org/en/content/articlelanding/2012/cc/c1cc16050h