Page 222 - Book Hosokawa Nanoparticle Technology Handbook

FUNDAMENTALS CH. 4 CONTROL OF NANOSTRUCTURE OF MATERIALS

60 25 estimated from the fitting by equation (4.3.1) to the
dependence in Fig. 4.3.12. The maximum film thick-
ness strongly depends on the reaction pH. The hydrol-
50
20 ysis reaction rate increases with decreasing pH, while
the adsorption is related to the charge of the spices in
40 solution and at the particle surface. At a pH below the
15 isoelectric point of silica, there is an electrostatic attrac-
δ M (nm) 30 κ(10 -6 x s -1 ) tion between the silica precursors and the negatively
10 charged PS particles due to the opposite charges.
20 Figure 4.3.14(a) shows that the silica-coated PS
particles can be close-packed by centrifuging. Porous
5
10

0 0
1 2 3 4
pH
Figure 4.3.13
Relationship between reaction pH and maximum silica
film thickness ( ; circle) and rate constant ( ; triangle).
M

Figure 4.3.14 Figure 4.3.15
SEM micrographs of close-packed structures formed by SEM micrographs of ordered porous silica materials
centrifuging silica-coated PS particles (a) prior to sintering produced by sintering silica-coated PS particles: (a) pH 1.5;
and (b) after sintering. (b) pH 2; (c) pH 3.

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