Rod-like particles growing in sol–gel processing of 1:1 molar mixtures of 3-glycidoxypropyl­tri­meth­oxy­silane and tetra­eth­oxy­silane

The growth kinetics and the structure of organic/silica hybrids prepared from acid hydrolysis of 1:1 molar mixtures of 3-glycidoxypropyl­tri­meth­oxy­silane and tetra­eth­oxy­silane were studied by small-angle X-ray scattering (SAXS) at 315, 325 and 335 K. The evolution of the SAXS intensity is compatible with the growth of silica-rich domains by aggregation from a fixed number of primary particles. Two distinct growth regimes could be identified by analyzing the relation I(0) ∝ R_g^D between the intensity extrapolated to zero I(0), the radius of gyration R_g of the aggregates and the exponent D, which gives information on the geometry and the mechanism of growth of the aggregates. An initial period was attributed to the growth of rod-like particles with approximately the same radius and variable length. At more advanced degrees of aggregation the process was controlled by the growth of larger aggregates with higher-order dimensionality. A narrow distribution of cylinder lengths given by the Schulz function fitted the experimental SAXS data well during the most part of the initial regime of cylindrical particle growth. These particles were later found as rod-like subunits of the larger aggregates grown at more advanced degrees of aggregation. Some condensation possibilities yielding the formation of structures compatible with those inferred from the present study are discussed.