Understanding The Effect Of Rigidity On The Conformation And Dynamical Evolution Of Polymer In Shear Flow

The analysis of the conformation and dynamic evolution of polymer chains in simple shear flow at micro scale provide a theoretical basis for a deep understanding of microfluidic separation and macro rheological behavior and also have a guiding significance for the "customized" properties of polymer materials.Besides,the rigidity of polymer is one of the basic factors in affecting the conformation and dynamic behaviors of polymer chains.Therefore,it remains an important research topic of polymer science to clarify the influence of chain rigidity.Although it is possible to observe the deformation of single polymer with the rapid development of micro technology nowadays,the role of a single atom of a chain and the influence of chain rigidity on the conformational change and dynamics are still difficult to be obtained by experimental measures.However,the dynamic trajectories of polymer chains can be obtained by means of computational simulation,which makes it possible to establish appropriate models in understanding these problems.In this paper,the molecular dynamics(MD)coupled with multiparticle collision dynamics(MPCD)are introduced in the study of conformation and dynamics of polymer chains with graph theory analysis.??The conformational and dynamical evolution for semiflexible polymer chains in shear flow.(1)The conformation of linear polymer chain in shear flow will express obvious periodic behavior,including collapse,tumble,stretch and align&flip.All semiflexible chains experience quasi-periodic tumbling motions when the shear strain overwhelms the U-shape(or S-shape)deformation energy barrier(Wi>1).(2)The scaling relationship between the critical orientation angle and Wi is ?C?Wi-1/3,slightly depending on chain rigidity;the scaling relationship between the characteristic tumbling time is ?tb?Wi-0.65,independent on rigidity.(3)By analyzing the differential contact map,at high shear flow,the collapse prefers to relax from chain ends,and the stretching starts from the center of the chain,followed by a dumbbell-or half dumbbell-like extension.At the intermediate shear rate flow,flexible polymer presents a quasi-affine deformation followed by the extension of dumbbell-like ends while semiflexible ones exhibit significantly different deformation process to relax shear stress in flow.??The conformation evolution and dynamics of block copolymers in simple shear flow.(1)Compared with the proportion between rigid and flexible blocks,the type of the central blocks plays a more important role in the conformational and dynamical evolution of copolymers.If the central block is a coil,the copolymer chain takes end-over-end tumbling motion,while if the central block is a rod,the copolymer chain undergoes U-shape or S-shape deformation at mid shear rate.(2)As the shear strength increases,all copolymers behave more and more like flexible polymers at high shear rate.This can be attribute to that shear flow is strong enough to overcome the buckling force of the rigid blocks.??The conformation evolution of polyurethane chain in shear flow.(1)Under low shear rate or equilibrium state,the PU chains remain to be compression sphere due to the hydrogen bond adsorption inner.And the mean square radius of gyration will be smaller with the increase of hydrogen strength and the ratios of rigid block nearly have no effect on in.(2)With the shear rate increase,the PU chains with lower hydrogen strength are easily to be stretch and become a chain-spherical deformation,which means the aggregation happened between rigid block and flexible block keeps straight to relax shear strength.In this situation,the out coming and stability of chain-spherical conformation will be improved by increasing the proportion of rigid block or raising the hydrogen bond strength.(3)When the shear rate keeps increasing,the shear strength is strong enough to overcome the hydrogen energy inner PU chain,the PU chain will undergo periodic rolling similar with flexible chain.However,due to the existence of hydrogen bonds,the complete stretching state is not stable and will collapse rapidly.And the PU chains with a higher ratio of rigid block need higher shear strength to stretch their conformation.