Molecular Simulation On The Dynamics Of ? State In Polymer Solutions

How to define the ? point of polymer solutions from dynamic behaviors remains one of the open problems in polymer physics.We study the dynamic behavior of ideal state in dilute polymer solutions by dissipative particle dynamics simulation.We find that the fluctuation of gyration radius is large for short chains(N-100),due to the strong inter-chain interaction.It becomes unreasonable to identify the transition state by the traditional method of using the gyration radius.Results show that dynamic structure factor could well quantify the transition point.We find several modes related to internal motions of intrachain interaction.As approaching the ? point,all the slow mode at the spectrum ?>l(ns)-1 vanish,leaving only the fast mode at ??0.66(ns)-1.Moreover,the spectral density at the fast mode reaches a maximum value nearby the ? point.We suggest that,at the ? point,the chain conformation relaxes to its most probable distribution only by the slow mode.We can give a new definition of the dynamics of the ? point from these results.