| Because of their unique cyclic structure,ring polymers exhibit remarkable difference in size and dynamic properties.Therefore,ring polymers have been widely concerned by scholars in the fields of polymer physics,polymer materials,biophysics,and chemistry and chemical engineering.The rheological characteristics of linear polymer melts could be improved greatly by adding a small amount of ring polymers,such as the significant increase of the viscosity.As a result,the blends system containing ring polymers is one of the most promising functional composite systems.However,there are still many basic problems unsolved in the static and dynamic properties of ring polymers in monodisperse polymer melts,ring-linear polymer blends melts,and bidisperse polymer melts,which seriously limits the precise regulation and diversified application of the systems containing ring polymers.From the perspective of theories,the solution of the conformational problem for ring melts is hampered because the Hamiltonian representation of the topological constraints has not been found.From the experimental point of view,although the techniques fo synthesis,characterization,and purification of ring polymers(i.e.,size exclusion chromatography,liquid chromatography under critical conditions,and small angle neutron scattering experiments)has made long-term progress,there are inevitably some impurities in the ring melts.Therefore,employing the dynamic Monte Carlo simulations based on the bond-fluctuation model and combining primitive path analysis and the geometric methodology,we systematically investigate the static and dynamic properties of the ring polymer in monodisperse polymer melts,ring-linear polymer blends melts,and bidisperse ring polymer melts.And we elucidate the molecular mechanism of the dynamic properties of the ring polymer in different melts.The primary results are summarized as follows:1.Size and dynamics of ring polymers under different topological constraints.The scaling exponent of the chain length for the mean-square radius of gyration decreases with the increasing chain length for ring polymer in melts,which is totally different from that for linear polymers.The distinctive closing structure of ring polymers also results in the unusual dynamic characteristics.However,there are still many discrepancies in these features and the physical mechanisms behind these phenomena are urged to be further studied.Using dynamic Monte Carlo simulaiton model,we obtained a series of results.(1)The structural relaxation time of ring polymers in melts is affected by both the intermolecular and intramolecular topological constraints.The scaling relationship between self-diffusion coefficient and chain length is dominated by the intermolecular constraints and the intramolecular constraints affect only the value of self-diffusion coefficient and have little influence on the scaling relationship.(2)Because of the different effects of intermolecular and intramolecular topological constraints on the structural relaxation time and self-diffusion coefficient,the translational diffusion and rotational relaxation of are decoupled over a long time scale,which results in the breakdown of the extended Stokes-Einstein relation(Dτ～N).(3)There is a long-time non-Fickian diffusion for long ring polymers in melts,and the time scale is 10 times larger than the time that ring polymers diffuse to the distance of their own size.The intermolecular interaction is the reason for the long-time nonFickian diffusion and the main mode of the interaction is ring-ring threading rather than"cage" effect.2.Size and dynamics of a tracer ring polymer in linear polymer chain melts.The ring-linear polymers blends system is one of the most promising functional composite systems.However,the existing theories cannot describe the size,structural relaxation time,and self-diffusion coefficient of ring polymers in the belnds perfectly.By employing the dynamic Monte Carlo simulations of the bond-fluctuation model along with the primitive path analysis and the geometric methodology,we systematically investigated the static and dynamic properties of a tracer ring in a linear melt and clarified several disputes of previous studies.(1)The topological constraints between the tracer ring and linear matrix chains do not change the size of the tracer ring polymer.The scaling exponent of the ring polymer length for its mean-square radius of gyration decrease to 0.5 from 0.6 with the increase of the linear chain length.This occurs because the ring-linear threading contributes to the swell of the ring chain;meanwhile,the screening effect from the linear matrix on the ring chain becomes stronger with increasing linear chain length.(2)Ring-linear threading is an important factor affecting the dynamic properties of ring polymers.However,there are many discrepancies between the scaling relationship and the physical picture depicted by the existing theories(the Restraint Reptation mechanism,the Once-Threaded mechanism,and the Constraint Release mechanism),i.e.,these theories can not explain the dynamics of the tracer ring polymer in a linear chain melt.Therefore,we propose the"touch-threading" mechanism,which could be regarded as an important supplement to the above mechanisms,to describe the structural relaxation and translational diffusion of a tracer ring in a linear chain melt.(3)For a tracer ring polymer in a long linear chain melt,the extended Stokes-Einstein relation breaks down.This is because the strong topological constraints of the ring-linear threading slows down the diffusion of the tracer ring polymer,resulting in the structural relaxation and translational diffusion.3.Size and dynamics of a tracer ring polymer in ring polymer melts matrix.Besides the influence of the ring polymers in melts and the linear matrix chains on the tracer ring polymer,we have also studied the impact of the ring polymers with different lengths on the size and dynamics of a tracer ring polymer.Using dynamic Monte Carlo simulaiton model,the following results are obtained.(1)When the chain length of the the ring polymer melts matrix is larger than that of the tracer ring polymer,the scaling exponent of the tracer ring chain length for the length of the the ring polymer melts matrix is-0.1,which is larger than the result of theoretical prediction.(2)The influence of the ring polymer melts matrix on the structural relaxation time of the tracer ring polymer can be neglected but is quite important on the self-diffusion coefficient of the tracer ring polymer.Compared with the linear polymer melts,the ring polymer melts matrix hinders the translational diffusion of the tracer ring polymer more slightly.Because the topological constraints of the ring-ring threading are much weaker than thoes of the ring-linear threading.(3)The extended Stokes-Einstein relation holds for the tracer ring polymer in a short ring polymer melts matrix but breaks down for that in a long ring polymer melts matrix. |
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