Having highly tunable molecular topology is one of the most important characteristics of polymers that provides these materials with a wide range of interesting and unique properties.In particular,ring polymers exhibi...Having highly tunable molecular topology is one of the most important characteristics of polymers that provides these materials with a wide range of interesting and unique properties.In particular,ring polymers exhibit a number of properties that are markedly distinct from their linear counterparts.Here,we compare and contrast the glass formation of unknotted,nonconcatenated ring and linear polymer melts having variable molecular mass based on molecular dynamics simulations of a coarse-grained model.After revealing an unusual property in the structure of small rings,we discuss the mass dependence of the structural relaxation time determined from the self-intermediate scattering function over a wide range of temperatures in both ring and linear polymers.As a general trend,we find that the characteristic temperatures(e.g.,the glass transition temperature)and fragility of glass formation increase with increasing molecular mass in linear polymers,but the mass dependences of these properties are rather weak in the family of ring polymer models considered,in broad accord with experimental measurements.Importantly,we show that the glass formation of ring polymers can quantitatively be described by the string model,a model that is broadly consistent with the entropy theory of glass formation and that takes the mass of string-like clusters as a molecular realization of the abstract cooperatively rearranging regions.This opens the possibility of applying the configurational entropy-based theories to describe the glass formation of ring polymers,once the ring topology is taken into account.展开更多
Stretching polymer in fluid flow is a vital process for studying and utilizing the physical properties of these molecules,such as DNA linearization in nanofluidic channels.We studied the role of hydrodynamic interacti...Stretching polymer in fluid flow is a vital process for studying and utilizing the physical properties of these molecules,such as DNA linearization in nanofluidic channels.We studied the role of hydrodynamic interactions(His)in stretching a free star polymer in Poiseuille flow through a tube using mesoscale hydrodynamic simulations.As increasing the flow strength,star polymers migrate toward the centerline of tube due to His,whereas toward the tube wall in the absence of His.By analyzing the end monomer distribution and the perturbed flow around the star polymer,we found that the polymer acts like a shield against the flow,leading to additional hydrodynamic drag forces that compress the arm chains in the front of the star center toward the tube axis and lift the arm chai ns at the back toward the tube wall.The balanced hydrodynamic forces freeze the polymer into a trumpet structure,where the arm chains maintain a steady strongly stretched state at high flow strength.In contrast,the polymer displays remarkably large conformational change when switching off His.Our simulation results explained the coupling between His and the structure of star polymers in Poiseuille flow.展开更多
基金financially supported by the National Natural Science Foundation of China(Nos.22222307 and 21973089)。
文摘Having highly tunable molecular topology is one of the most important characteristics of polymers that provides these materials with a wide range of interesting and unique properties.In particular,ring polymers exhibit a number of properties that are markedly distinct from their linear counterparts.Here,we compare and contrast the glass formation of unknotted,nonconcatenated ring and linear polymer melts having variable molecular mass based on molecular dynamics simulations of a coarse-grained model.After revealing an unusual property in the structure of small rings,we discuss the mass dependence of the structural relaxation time determined from the self-intermediate scattering function over a wide range of temperatures in both ring and linear polymers.As a general trend,we find that the characteristic temperatures(e.g.,the glass transition temperature)and fragility of glass formation increase with increasing molecular mass in linear polymers,but the mass dependences of these properties are rather weak in the family of ring polymer models considered,in broad accord with experimental measurements.Importantly,we show that the glass formation of ring polymers can quantitatively be described by the string model,a model that is broadly consistent with the entropy theory of glass formation and that takes the mass of string-like clusters as a molecular realization of the abstract cooperatively rearranging regions.This opens the possibility of applying the configurational entropy-based theories to describe the glass formation of ring polymers,once the ring topology is taken into account.
基金supported by the National Natural Science Foundation of China(Nos.21574134,21774127,21790342,and 21504093)the Key Research Program of Frontier Sciences,CAS(No.QYZDY-SSW-SLH027).
文摘Stretching polymer in fluid flow is a vital process for studying and utilizing the physical properties of these molecules,such as DNA linearization in nanofluidic channels.We studied the role of hydrodynamic interactions(His)in stretching a free star polymer in Poiseuille flow through a tube using mesoscale hydrodynamic simulations.As increasing the flow strength,star polymers migrate toward the centerline of tube due to His,whereas toward the tube wall in the absence of His.By analyzing the end monomer distribution and the perturbed flow around the star polymer,we found that the polymer acts like a shield against the flow,leading to additional hydrodynamic drag forces that compress the arm chains in the front of the star center toward the tube axis and lift the arm chai ns at the back toward the tube wall.The balanced hydrodynamic forces freeze the polymer into a trumpet structure,where the arm chains maintain a steady strongly stretched state at high flow strength.In contrast,the polymer displays remarkably large conformational change when switching off His.Our simulation results explained the coupling between His and the structure of star polymers in Poiseuille flow.
