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Statics,Dynamics and linear viscoelasticity from Dissipative Particle Dynamics Simulation of Entangled linear Polymer Melts

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Chinese Journal of Polymer Science 2023年第9期41卷 1392-1409,I0007页

作者： Fan Wang Lu-Kun Feng Ye-Di Li Hong-Xia Guo Beijing National Laboratory for Molecular Sciences Joint Laboratory of Polymer Sciences and MaterialsState Key Laboratory of Polymer Physics and ChemistryInstitute of ChemistryChinese Academy of SciencesBeijing100190China University of Chinese Academy of Sciences Beijing100049China

Dissipative particle dynamics(DPD)with bond uncrossability shows a great potential in studying entangled polymers,however relatively little is known of applicability range of entangled DPD model to be use as a model for ideal chains and properly describe the full dynamics of entangled ***,we perform a comprehensive study on structure,dynamics and linear viscoelasticity of a typical DPD entangled model system,semiflexible linear polymer *** polymers obey Flory's ideality hypothesis in chain dimensions,but their local structure exhibits nonideal behavior due to weak correlated hole *** monomer motion and viscoelasticity relaxation reproduce the full pictures as predicted by reptation *** stronger chain length dependent diffusion coefficient and relaxation time as well as dynamic moduli are in close agreement with predictions of modern tube model that accounts for additional relaxation mechanisms besides chain ***,an anomalous sub-diffusive center of mass motion is observed both before and after the intermediate reptation regime and the cross-correlation between chains is not negligible even these polymers obey stress-optical law,indicating limitations of the reptation *** semiflexible linear entangled DPD model can correctly describe statics and dynamics of entangled polymer melts.

关键词： Entangled polymer melts Dynamics linear viscoelasticity Dissipative particle dynamics

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The Effectiveness of the Havriliak-Negami Model in Predicting the Master Curves of the Asphalt Blends with SBS Triblock Copolymer and Organic-Montmorillonite at Different Temperatures and Frequencies

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Journal of Materials Science and Chemical Engineering 2024年第7期12卷 23-39页

作者： María Ángeles Vargas-Hernández Miguel Ángel Vargas Pedro R. García-Morán Humberto Vázquez-Torres Divisin de Ingeniera Qumica y Bioqumica TecNMTecnolgico de Estudios Superiores de Ecatepec Edo. de Mxico Mxico Facultad de Qumica Universidad Nacional Autonma de Mxico Cd. de Mxico Mxico Facultad de Ciencias Bsicas Ingeniera y Tecnologa Universidad Autnoma de Tlaxcala Tlaxcala Mxico Departamento de Fsica Universidad Autnoma Metropolitana-Iztapalapa Cd. de Mxico Mxico

The dynamic viscoelastic properties of asphalt AC-20 and its composites with Organic-Montmorillonite clay (OMMt) and SBS were modeled using the empirical Havriliak-Negami (HN) model, based on linear viscoelastic theory (LVE). The HN parameters, α, β, G0, G∞and τHN were determined by solving the HN equation across various temperatures and frequencies. The HN model successfully predicted the rheological behavior of the asphalt and its blends within the temperature range of 25˚C - 40˚C. However, deviations occurred between 40˚C - 75˚C, where the glass transition temperature Tg of the asphalt components and the SBS polymer are located, rendering the HN model ineffective for predicting the dynamic viscoelastic properties of composites containing OMMt under these conditions. Yet, the prediction error of the HN model dropped to 2.28% - 2.81% for asphalt and its mixtures at 100˚C, a temperature exceeding the Tg values of both polymer and asphalt, where the mixtures exhibited a liquid-like behavior. The exponent α and the relaxation time increased with temperature across all systems. Incorporating OMMt clay into the asphalt blends significantly enhanced the relaxation dynamics of the resulting composites.

关键词： Asphalt Blends Master Curve linear viscoelasticity Havriliak-Negami Model

A revisit of strain-rate frequency superposition of dense colloidal suspensions under oscillatory shears

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Journal of Central South University 2016年第8期23卷 1873-1882页

作者：李俊杰程璇张颖孙尉翔 Department of Mathematics and Applied Mathematic Xiamen University Fujian Key Laboratory of Advanced Materials Xiamen University Department of Materials Science and Engineering College of Materials Xiamen University Research Institute of Materials Science and State Key Laboratory of Luminescent Materials and Devices South China University of Technology

Strain-rate frequency superposition(SRFS) is often employed to probe the low-frequency behavior of soft solids under oscillatory shear in anticipated linear response. However, physical interpretation of an apparently well-overlapped master curve generated by SRFS has to combine with nonlinear analysis techniques such as Fourier transform rheology and stress decomposition method. The benefit of SRFS is discarded when some inconsistencies of the shifted master curves with the canonical linear response are observed. In this work, instead of evaluating the SRFS in full master curves, two criteria were proposed to decompose the original SRFS data and to delete the bad experimental data. Application to Carabopol suspensions indicates that good master curves could be constructed based upon the modified data and the high-frequency deviations often observed in original SRFS master curves are eliminated. The modified SRFS data also enable a better quantitative description and the evaluation of the apparent structural relaxation time by the two-mode fractional Maxwell model.

关键词： strain-rate frequency superposition medium amplitude oscillatory shear linear viscoelasticity fractional Maxwell model

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Correlation of Two Coupled Particles in Viscoelastic Medium

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Communications in Theoretical Physics 2006年第2X期46卷 353-361页

作者： XIE Bai-Song Key Laboratory of Beam Technology and Materials Modification of Ministry of Education Beijing Normal University Beijlng 100875 China Institute of Low Energy Nuclear Physics Beijing Normal University Beijing 100875 China Department of Physics Xinjiang University Urumqi 830046 China The Abdus Salam International Centre for Theoretical Physics Strada Costiera 11 34014 Trieste Italy

Considering the viscoelastic memory effect, we study the correlated motion of two hydrodynamically coupled colloidal particles, each of which confined in a harmonic potential well, in a Kelvin-type and Maxwell-type viscoelastic medium. We find that viscoelastic relaxation plays a significant role in modifying the correlation, particularly the cross correlation. We also find that both the real and imaginary parts of the response function are significantly different from the viscous medium case. In particular there is a phase shift between the vanishing imaginary part and the maximal real part of the response function in a viscoelastic medium. In addition imaginary part of the cross correlation response function exhibits a net energy loss （gain） behavior when the elasticity parameter of the medium is larger （smaller） than the critical value for Kelvin （Maxwell） viscoelastic fluid. Some implication of our results and their connection with previous works are discussed.

关键词： linear viscoelasticity particle dynamics colloids

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Hyperbolic Divergence Cleaning in Lattice Boltzmann Magnetohydrodynamics

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Communications in Computational Physics 2023年第1期33卷 245-272页

作者： Paul J.Dellar OCIAM Mathematical InstituteUniversity of OxfordRadcliffe Observatory QuarterOxford OX26GGUK

Magnetohydrodynamics couples the Navier-Stokes and Maxwell’s equations to describe the flow of electrically conducting fluids in magnetic ***’s equations require the divergence of the magnetic field to vanish,but this condition is typically not preserved exactly by numerical *** can develop artifacts because structural properties of the magnetohydrodynamic equations then fail to *** with hyperbolic divergence cleaning permits a nonzero divergence that evolves under a telegraph equation,designed to both damp the divergence,and propagate it away from any sources,such as poorly resolved regions with large spatial gradients,without significantly increasing the computational *** show that existing lattice Boltzmann algorithms for magnetohydrodynamics already incorporate hyperbolic divergence cleaning,though they typically use parameter values for which it reduces to parabolic divergence cleaning under a slowly-varying *** recover hyperbolic divergence cleaning by adjusting the relaxation rate for the trace of the tensor that represents the electric field,and absorb the contribution from the symmetric-traceless part of this tensor using a change of *** experiments confirm that the qualitative behaviour changes from parabolic to hyperbolic when the relaxation time for the trace of the electric field tensor is increased.

关键词： Magnetohydrodynamics divergence cleaning telegraph equations matrix collision operators linear viscoelasticity

Something Old, Something New, in Rheometry

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Something Old, Something New, in Rheometry