T. Sintes, R. Toral and A. Chakrabarti
The silica polymerization proceeds in two steps:
(1) Hydrolysis
(2) Condensation
It is possible to vary the functionality number distribution of
hydrolyzed sites by chanching the 
molecular concentration ratio and, as a consequence,
morphologically different structures are generated.
We present here a systematic study for a whole set of tetra-, tri-, di-, and
mono-functional monomer distribution, denoted as 
,
with 
for n=1,2,3,4.
Figure 1: Silica aggregates containing 50000 sites grown on a tetragonal lattice.
Picture (a) corresponds to a functionality distribution of (1:0:0:0);
picture (b) to (3:3:3:1) and picture (c) to (0:1:1:0).
The large k behavior of 
has the form:
correspond to mass fractals with 
,
characterize a surface fractal with 
.
Figure 2: Log-log plot of the static structure factor, 
,
for large k values for different
functionality distributions. The straight lines are the best fit to
the data. The slopes of the lines yield the 
value characterizing the
and surface fractals. 
, 
, and 
correspond to the pictures
shown in the color plate. Each plot has been shifted by an arbitrary
amount in the vertical axis for the sake of clarity.