  Irreversible diffusion limited cluster aggregation (DLCA) of hard spheres was
simulated using Brownian cluster dynamics. Bound spheres were allowed to move
freely within a specified range, but no bond breaking was allowed. The
structure and size distribution of the clusters was investigated before
gelation. The pair correlation function and the static structure factor of the
gels were determined as a function of the volume fraction and time. Bond
flexibility led to local densification of the clusters and the gels, with a
certain degree of order. At low volume fractions densification of the clusters
occurred during their growth, but at higher volume fractions it occurred mainly
after gelation. At very low volume fractions, the large scale structure
(fractal dimension), size distribution and growth kinetics of the clusters was
found to be close to that known for DLCA with rigid bonds. Restructuring of the
gels continued for long times, indicating that aging processes in systems with
strong attraction do not necessarily involve bond breaking. The mean square
displacement of particles in the gels was determined. It is shown to be highly
heterogeneous and to increase with decreasing volume fraction.
