Early stages of homopolymer collapse

Interest in the protein folding problem has motivated a wide range of theor etical and experimental studies of the kinetics of the collapse of flexible homopolymers. In this paper, a phenomenological model is proposed for the kinetics of the early stages of homopolymer collapse following a quench fro m temperatures above to below the theta temperature. In the first stage, na scent droplets of the dense phase are formed, with little effect on the con figurations of the bridges that join them. The droplets then grow by accret ing monomers from the bridges, thus causing the bridges to stretch. During these two stages, the overall dimensions of the chain decrease only weakly. Further growth of the droplets is accomplished by the shortening of the br idges, which causes the shrinking of the overall dimensions of the chain. T he characteristic times of the three stages scale as N-0, N-1/5, and N-6/5, respectively, where N is the degree of polymerization of the chain. PACS n umber(s): 36.20.-r, 61.25.Hq, 83.10.Nn, 87.15.-v.