  We study a chemical gelation model in two dimensions which includes both
monomer aggregations and bond fluctuations. Our numerical simulation shows that
a sol-gel transition occurs when an initial monomer concentration is above a
critical concentration. Fractal aggregates grow until the sol-gel transition
occurs. After the gelation, however, bond fluctuations break the fractal
structure and a novel inhomogeneous gel fibre network appears instead. A pore
size distribution of the inhomogeneous structure shows the existence of
hierarchical structures in the gel phase. It is also found that slow dynamics
appear near the critical concentration.
