Minor local disturbances can lead to undesirable by-products due to the inherent chaotic behaviour of the process. It is known that the silica material initially consists of small particles that aggregate into a gel structure. This gelling process has been characterised as a colloidal aggregation leading to ramified aggregate morphologies. These parameters influence the formation of bonds between particles by influencing the properties of the particles. For instance a change in pH influences the charge of the particle surface.
Charged surfaces repel and consequently the interaction between particles is affected.
Similarly, other parameters affect the aggregation process at the molecular level, leading to a complex reaction system which is intrinsically chaotic. The fresh gel morphology is weak and cannot survive harsh treatment like drying. Capillary forces destroy the vulnerable links between particles and lead to the production of a dense amorphous product rather than a porous gel with high surface area. After gelation, ageing processes become dominant. These processes can reinforce the weak gel structure by additional bond formation inside the backbone or by addition of silica particles from the solution to the backbone.