Molecular dynamics study on the structure and relaxation of short-chain branched ring polymer melts

Roh, Eun; Kim, Jun Mo; Baig, Chunggi

doi:10.1016/j.polymer.2019.05.002

Cited by 18 publications

(12 citation statements)

References 49 publications

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“…In the community, linear and cyclic polymers with sidechain grafts are generally called linear graft and cyclic graft polymers, respectively. − In particular, the studies on the preparation and application of cyclic graft polymers have attracted increasing interest in the last decade. − Namely, by the grafting-from method, Zhong et al prepared cyclic graft c -PEO- g -PS copolymers, where PEO represents the poly(ethylene oxide) cyclic backbone and PS represents polystyrene sidechain grafts. They found that c -PEO- g -PS with longer sidechains shows a lower critical micelle concentration (CMC) .…”

Section: Introductionmentioning

confidence: 99%

Study of Linear and Cyclic Graft Polystyrenes with Identical Backbone Contour in Dilute Solutions: Preparation, Characterization, and Conformational Properties

et al. 2022

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Exploring the difference in the topology−structure−conformation relationship for linear and cyclic graft polymers is an interesting topic. In this work, two libraries of linear graft (l-PPA-g-PS, with a linear backbone) and cyclic graft (c-PPAg-PS, with a cyclic backbone) polystyrenes with low ratios of the backbone-to-sidechain contour length (r c , from 1.26 to 6.22) and various grafting densities (σ, from 0.16 to 0.86) have been studied as models. Atomic force microscopy (AFM) characterization has indicated ellipsoidal and spherical morphologies for both l-PPA-g-PS and c-PPA-g-PS with no significant difference. By comparing the absolute (M w,abs ) and apparent (M w,app ) molar masses, it is found that M w,abs /M w,app varies from 1.5 to 3.5 and gradually increases with σ. By measuring g h 1/2 (g h 1/2 = R h,graft /R h,linear ), it is found that the two topologies have different compactness of conformation. By following the temperaturedependent interchain aggregation in cyclohexane, it is found that the cyclic backbone feature can suppress the interchain association and be more susceptible to graft density than linear graft polymers. The present study has clearly showed that the cyclic graft topology can potentially display unique structural and conformational properties, which can be attributed to the topological advantages such as more compact conformation and significant isotropic features.

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Section: Introductionmentioning

confidence: 99%

Study of Linear and Cyclic Graft Polystyrenes with Identical Backbone Contour in Dilute Solutions: Preparation, Characterization, and Conformational Properties

et al. 2022

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“…For accurate molecular-level analysis, we conducted atomistic NEMD simulations for each system based on the standard p -SLLOD algorithm implemented with a Nosé–Hoover thermostat under Lees–Edwards boundary conditions. − The pure linear and ring PE systems were simulated with the Siepmann–Karaboni–Smit (SKS) united-atom (UA) potential model, whereas SCB linear and SCB ring systems were simulated using the Transferable Potentials for Phase Equilibria (TraPPE) UA potential model because both models are well known to give accurate predictions of the structural and dynamical properties of alkanes and PE molecules. ,− ,− ,, In these models, CH m ( m = 1, 2, or 3) are typically treated as a UA unit by incorporating the relatively small hydrogen atom(s) into the carbon atom. The set of evolution equations for all PE systems was numerically integrated via the reversible Reference System Propagator Algorithm (r-RESPA) with two distinct time scales: a short time scale (0.47 fs) for bonded (bond-stretching, bond-bending, and bond-torsional) interactions and a long time scale (2.35 fs) for nonbonded Lennard–Jones (LJ) interactions, a thermostat, and an external flow field (see the Supporting Information for details of the simulation method).…”

Section: Systems Studied and Simulation Methodsmentioning

confidence: 99%

“…Another important class of polymeric materials is the short-chain branched (SCB) polymer wherein very short branches [typically below the characteristic Kuhn length, e.g., two, four, or six carbon atoms in polyethylene (PE) molecules] are incorporated along the chain backbone. , Recent numerical studies demonstrated that the fast random thermal Brownian motions of short branches, in association with their very short characteristic relaxation time, generally make the overall chain structure of SCB polymers more compact and less deformable against the applied flow field. − Coarse-grained Brownian dynamics (BD) simulations of SCB linear polymers showed that as the density of short branches along the backbone increased, the structural deformability of the SCB chains under shear flow diminished . More importantly, the rheological characteristics of SCB polymers under shear and elongational flows were found to be drastically changed by altering the spatial distribution of the short branches along the main backbone. , These studies clearly showed the critical role of short branches in the general structural and dynamic behaviors of polymeric materials.…”

Section: Introductionmentioning

confidence: 99%

Melt Rheology of Short-Chain Branched Ring Polymers in Shear Flow

Jeong

Cho

et al. 2021

Macromolecules

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We examined the general rheological characteristics of short-chain branched (SCB) ring polyethylene (PE) melts using atomistic nonequilibrium molecular dynamics (NEMD) simulations under shear in a wide range of flow strengths. To analyze the synergetic influence of the closed-loop ring geometry and short-chain branching on the structural and rheological behavior of polymeric systems, the results for the SCB ring PE melt were directly compared with those of the corresponding linear, ring, and SCB linear analogues. The ring geometry generally induces a more compact chain structure and a lower degree of chain orientation in the flow direction under shear. By means of the intrinsically fast random dynamics of short branches, short-chain branching also leads to a more compact structure and a lower degree of structural deformation against the applied flow. From the observation of their respective roles in the polymer structure and dynamics, the combination of the ring topology and short-chain branching resulted in distinctive synergistic characteristics. Specifically, relative to the rather small difference in shear-thinning behavior between the pure linear and ring PE melt systems, a noticeably large difference was observed between the corresponding SCB linear and ring PE systems, with this discrepancy becoming even stronger at higher flow strengths. The significant enhancement in shear viscosity for the SCB ring system is attributed to the existence of highly extended SCB ring chains in association with their tight topological linking (inter-ring threading) via enhanced interchain branch−branch and branch−backbone interactions.

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“…The properties of the branched polymer in equilibrium and nonequilibrium conditions have been investigated by theoretical analysis [ 25 , 26 , 27 , 28 , 29 ], experiments [ 24 , 26 , 27 , 30 , 31 , 32 , 33 ] and simulations [ 9 , 34 , 35 , 36 , 37 , 38 , 39 ]. The influence of long-chain branching on the rheological properties of conventional polyolefins, such as polyethylene (PE) [ 40 , 41 , 42 , 43 , 44 ] and polypropylene (PP), has been investigated [ 45 , 46 , 47 ].…”

Section: Introductionmentioning

confidence: 99%

Dynamical and Structural Properties of Comb Long-Chain Branched Polymer in Shear Flow

Wang

Wen

Zhang

et al. 2022

IJMS

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Using hybrid multi-particle collision dynamics (MPCD) and a molecular dynamics (MD) method, we investigate the effect of arms and shear flow on dynamical and structural properties of the comb long-chain branched (LCB) polymer with dense arms. Firstly, we analyze dynamical properties of the LCB polymer by tracking the temporal changes on the end-to-end distance of both backbones and arms as well as the orientations of the backbone in the flow-gradient plane. Simultaneously, the rotation and tumbling behaviors with stable frequencies are observed. In other words, the LCB polymer undergoes a process of periodic stretched–folded–stretched state transition and rotation, whose period is obtained by fitting temporal changes on the orientation to a periodic function. In addition, the impact induced by random and fast motions of arms and the backbone will descend as the shear rate increases. By analyzing the period of rotation behavior of LCB polymers, we find that arms have a function in keeping the LCB polymer’s motion stable. Meanwhile, we find that the rotation period of the LCB polymer is mainly determined by the conformational distribution and the non-shrinkable state of the structure along the velocity-gradient direction. Secondly, structural properties are numerically characterized by the average gyration tensor of the LCB polymer. The changes in gyration are in accordance with the LCB polymer rolling when varying the shear rate. By analyzing the alignment of the LCB polymer and comparing with its linear and star counterparts, we find that the LCB polymer with very long arms, like the corresponding linear chain, has a high speed to reach its configuration expansion limit in the flow direction. However, the comb polymer with shorter arms has stronger resistance on configuration expansion against the imposed flow field. Moreover, with increasing arm length, the comb polymer in shear flow follows change from linear-polymer-like to capsule-like behavior.

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Molecular dynamics study on the structure and relaxation of short-chain branched ring polymer melts

Cited by 18 publications

References 49 publications

Study of Linear and Cyclic Graft Polystyrenes with Identical Backbone Contour in Dilute Solutions: Preparation, Characterization, and Conformational Properties

Study of Linear and Cyclic Graft Polystyrenes with Identical Backbone Contour in Dilute Solutions: Preparation, Characterization, and Conformational Properties

Melt Rheology of Short-Chain Branched Ring Polymers in Shear Flow

Dynamical and Structural Properties of Comb Long-Chain Branched Polymer in Shear Flow

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