Dynamic scaling in an aggregating 2D Lennard-Jones system.

The evolution of a 2D Lennard-Jones system, quenched from the fluid to below the triple point, is simulated by molecular dynamics. We show that the structure factor obeys the scaling relation {ital S}{bold (}{ital q}/{ital q}{sub {ital m}}({ital t}){bold )} {similar_to}{ital q}{sub {ital m}}({ital t}){sup {minus}{ital d}{sub {ital f}}}{ital {tilde S}}({ital q}/{ital {tilde q}}{sub {ital m}}). Here {ital q}{sub {ital m}} is the location of the low angle peak in {ital S}({ital q}), {ital d}{sub {ital f}}=1.85{plus_minus}0.05 is a fractal dimension, and {ital {tilde S}}({ital q}/{ital {tilde q}}{sub {ital m}}) is a time-independent characteristic function which peaks at {ital {tilde q}}{sub {ital m}}. The quenching process is thermodynamically similar to the formation of a gel from a sol. Hence the relation suggests that a characteristic fractal dimension of even a dense gel can be derived from measurements of the time evolution of {ital S}({ital q}).