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Ralph H Colby - One of the best experts on this subject based on the ideXlab platform.
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terminal flow of cluster forming supramolecular polymer networks single chain relaxation or micelle reorganization
Physical Review Letters, 2020Co-Authors: Anto Mordvinki, Ralph H Colby, Diana Dohle, Wolfgang H Inde, Kay SaalwachteAbstract:We correlate the terminal relaxation of supramolecular polymer networks, based on unentangled telechelic poly(isobutylene) linear chains forming micellar end-group clusters, with the microscopic chain dynamics as probed by proton NMR. For a series of samples with increasing molecular weight, we find a quantitative agreement between the terminal relaxation times and their activation energies provided by rheology and NMR. This finding corroborates the validity of the transient-network Model and the special case of the sticky Rouse Model, and dismisses more dedicated approaches treating the terminal relaxation in terms of micellar rearrangements. Also, we confirm previous results showing reduction of the activation energy of supramolecular dissociation with increasing molecular weight and explain this trend with an increasing elastic penalty, as corroborated by small angle x-ray scattering data.
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linear viscoelastic and dielectric properties of phosphonium siloxane ionomers
ACS Macro Letters, 2013Co-Authors: Quan Chen, Siwei Liang, Huai Suen Shiau, Ralph H ColbyAbstract:The linear viscoelastic (LVE) and dielectric relaxation spectroscopic (DRS) properties of polysiloxanes with phosphonium (fraction f) and oligo(ethylene oxide) (fraction 1 – f) side groups with a fraction of ionic monomers f = 0–0.26 have been studied. LVE master curves of those ionomers have been constructed. The ionic dissociation has been witnessed as a delayed polymer relaxation in LVE with increasing ion content, as well as an α2 ionic segmental relaxation process in DRS. LVE exhibits glassy and delayed rubbery relaxation at low ionic fraction f ≤ 11%, where the ionic dissociation time detected in DRS enables description of LVE with a sticky Rouse Model. In contrast, the glassy and rubbery stress relaxation moduli merge into one broad process at high f ≥ 22%, where the whole LVE response from glassy to terminal relaxation can be described phenomenologically by a single Kohlrausch–Williams–Watts (KWW) equation with the lowest stretching exponent β = 0.10 ever seen for polymeric liquids, describing LVE...
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ionomer dynamics and the sticky Rouse Modela
Journal of Rheology, 2013Co-Authors: Quan Chen, Gregory J Tudryn, Ralph H ColbyAbstract:Linear viscoelastic (LVE) and dielectric relaxation spectroscopic (DRS) responses were examined for polyester ionomers based on polyethers and sulfonated phthalates with sodium counterions. For these ionomers, LVE shows both glassy and polymer relaxations increasingly delayed with increase of ionic content. DRS shows an α-relaxation process associated with the glass transition, followed by a ∼100× slower α2-relaxation process associated with ion rearrangements, before electrode polarization. A detailed comparison between LVE and DRS reveals that the α2 relaxation in DRS corresponds to a characteristic modulus of kT per ionic group, strongly suggesting that the molecular origin of the α2 relaxation is the dissociation/association of ion pairs from/into the ionic clusters. Based on this molecular picture, we can predict satisfactorily the LVE of the samples using a sticky Rouse Model by setting the α2 relaxation time as the lifetime of ionic associations. For ionomers based on poly(ethylene oxide), the association energy is 8–13 kJ/mol, causing only a short delay of the terminal relaxation beyond the delay in the glassy relaxation. In contrast, for ionomers based on the weaker solvating poly(tetramethylene oxide), the delay spans nine decades of frequency, analogous to a highly entangled polymer, yielding an association energy of 58 kJ/mol.Linear viscoelastic (LVE) and dielectric relaxation spectroscopic (DRS) responses were examined for polyester ionomers based on polyethers and sulfonated phthalates with sodium counterions. For these ionomers, LVE shows both glassy and polymer relaxations increasingly delayed with increase of ionic content. DRS shows an α-relaxation process associated with the glass transition, followed by a ∼100× slower α2-relaxation process associated with ion rearrangements, before electrode polarization. A detailed comparison between LVE and DRS reveals that the α2 relaxation in DRS corresponds to a characteristic modulus of kT per ionic group, strongly suggesting that the molecular origin of the α2 relaxation is the dissociation/association of ion pairs from/into the ionic clusters. Based on this molecular picture, we can predict satisfactorily the LVE of the samples using a sticky Rouse Model by setting the α2 relaxation time as the lifetime of ionic associations. For ionomers based on poly(ethylene oxide), the asso...
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structure and linear viscoelasticity of flexible polymer solutions comparison of polyelectrolyte and neutral polymer solutions
Rheologica Acta, 2010Co-Authors: Ralph H ColbyAbstract:The current state of understanding for solution conformations of flexible polymers and their linear viscoelastic response is reviewed. Correlation length, tube diameter, and chain size of neutral polymers in good solvent, neutral polymers in θ-solvent, and polyelectrolyte solutions with no added salt are compared as these are the three universality classes for flexible polymers in solution. The 1956 Zimm Model is used to describe the linear viscoelasticity of dilute solutions and of semidilute solutions inside their correlation volumes. The 1953 Rouse Model is used for linear viscoelasticity of semidilute unentangled solutions and for entangled solutions on the scale of the entanglement strand. The 1971 de Gennes reptation Model is used to describe linear viscoelastic response of entangled solutions. In each type of solution, the terminal dynamics, reflected in the terminal modulus, chain relaxation time, specific viscosity, and diffusion coefficient are reviewed with experiment and theory compared. Overall, the agreement between theory and experiment is remarkable, with a few unsettled issues remaining.
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Rouse Model OF STAR POLYMERS
American Chemical Society Polymer Preprints Division of Polymer Chemistry, 2008Co-Authors: Arnav Ghosh, Ralph H ColbyAbstract:2(and semidilute solutions inside their correlation length 3 ). The tube Models for entanglement effects give various approximations to solving Rouse motion of a chain confined by neighboring chains to a tube-like region. Consequently, the Rouse Model plays a central role in polymer dynamics. The Rouse Model for star polymers has been discussed extensively in the literature, first by Ham 5 in 1957. Presumably because of the non-trivial eigenvalues discussed below, Ham did not use the straightforward solution method of Rouse, but instead employed symmetry arguments borrowed from free electron theory of symmetric molecules like naphthalene. 6 With the advent of modern computers, the Rouse method of solving the coupled differential equations is actually quite routine. We solve the Rouse Model for star polymers, following the solution method Rouse used for linear polymers, 1
Lejun Wang - One of the best experts on this subject based on the ideXlab platform.
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influence of temperature on the solution rheology of cellulose in 1 ethyl 3 methylimidazolium chloride dimethyl sulfoxide
Cellulose, 2015Co-Authors: Fei Lu, Bowen Cheng, Lejun Wang, Chao Zhang, Yong HuangAbstract:Rheological properties of cellulose solutions in 1-ethyl-3-methylimidazolium chloride/dimethyl sulfoxide ([Emim]Cl/DMSO, 7/3, w/w) in a wide range of concentration and temperature were investigated. The viscosity of cellulose/[Emim]Cl/DMSO solution agrees well with the complex viscosity suggesting Cox–Merz law is valid for the solution. The viscosity contributed by cellulose (η 0–η s ) and cellulose concentration (c) scales as (η 0–η s )~c n with n in the range of 2.00–1.57 and 4.52–3.79 in semidilute unentangled and semidilute entangled regimes, respectively, in the temperature of 25–100 °C. Intrinsic viscosity of the solutions remains constant at temperature below 60 °C and decreases linearly with the increase of temperature above 60 °C. The activation energy of cellulose/[Emim]Cl/DMSO solution increases with the increase in cellulose concentration. The chain dynamics of cellulose in [Emim]Cl/DMSO follows Zimm Model and Rouse Model in dilute regime (lower than 0.5 wt%) and semidilute unentangled regime (between 0.5 and 2 wt%), respectively.
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viscoelasticity and rheology in the regimes from dilute to concentrated in cellulose 1 ethyl 3 methylimidazolium acetate solutions
Cellulose, 2013Co-Authors: Fei Lu, Bowen Cheng, Jun Song, Xiujie Ji, Lejun WangAbstract:Dynamic rheological behaviors of α-cellulose 1-ethyl-3-methylimidazolium acetate ([Emim]Ac) solutions were investigated in a large range of concentrations (0.1–10 wt %) at 25 °C. On the basis of data from the dynamic viscoelastic test, the exponents of the specific viscosity η sp versus concentration c were determined as 1.0, 2.0 and 4.7 for dilute, semidilute unentangled and entangled regimes respectively, which were in accordance with the scaling prediction for neutral polymer in θ solvent. The intrinsic viscosity [η] of the solution was determined to be 253 mL/g at 25 °C. The linear viscoelastic response of the dilute and semidilute unentangled solutions could be described successfully by the Zimm and Rouse Model (ν = 0.5 for θ solution) respectively, suggesting that the motion of cellulose chain in [Emim]Ac changed from Zimm to Rouse Model with increasing concentration. At low concentrations, failure of the Cox–Merz rule with steady shear viscosity larger than complex viscosity was observed. While as the concentration increased, the deviation from the Cox–Merz rule disappeared due to the formation of homogeneous entanglement structure in cellulose solution.
Yuliang Yang - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics simulation of associative polymers understanding linear viscoelasticity from the sticky Rouse Model
Journal of Rheology, 2021Co-Authors: Nuofei Jiang, Hongdong Zhang, Yuliang Yang, Ping TangAbstract:Polymers bearing associative groups (APs) are characterized by their fantastic viscoelastic behaviors. In a work recently published by our group [Jiang et al., Macromolecules 53, 3438–3451 (2020)], a single chain sticky Rouse Model (SRM) is proposed to describe the linear viscoelasticity of APs without the entanglement effect. In this work, equilibrium molecular dynamics simulation of an unentangled melt of an AP with uniformly distributed stickers is carried out, and the dynamic properties are simultaneously analyzed from the SRM. A chain Model with capped stickers is proposed so that a well-defined association chemistry is promised in the simulation system. The relative effective frictional coefficient of stickers, which is the key parameter in the SRM, is extracted from the chain center-of-mass diffusion, and it is found to be consistent with the dynamics of associative reaction in the fully gelated network. Based on this, a linear relaxation modulus and segmental diffusion functions are predicted from the SRM without fitting parameters, and these are found to quantitatively agree with the simulation results, showing the effectiveness of the SRM in connecting the dynamic properties at different molecular levels. The change in relaxation modes and the definition of the effective chain center are found to be crucial in the scenario of the SRM. Finally, the above analysis from the SRM is successfully extended to the simulation system with asymmetric chains. All these simulation results strongly support the SRM as a molecular Model for the linear rheology of AP.
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linear viscoelasticity of associative polymers sticky Rouse Model and the role of bridges
Macromolecules, 2020Co-Authors: Nuofei Jiang, Hongdong Zhang, Ping Tang, Yuliang YangAbstract:Polymers bearing associative groups can exhibit fascinating rheological behaviors. A modified version of the Rouse Model, which is originally used in block copolymers and called the sticky Rouse mo...
D Richter - One of the best experts on this subject based on the ideXlab platform.
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microscopic structure conformation and dynamics of ring and linear poly ethylene oxide melts from detailed atomistic molecular dynamics simulations dependence on chain length and direct comparison with experimental data
Macromolecules, 2017Co-Authors: Dimitrios G Tsalikis, Rossana Pasquino, Thanasis Koukoulas, Vlasis G Mavrantzas, Wim Pyckhouthintzen, A Wischnewski, Dimitris Vlassopoulos, M Monkenbusch, D RichterAbstract:We present results from very long (on the order of several microseconds) atomistic molecular dynamics (MD) simulations for the density, microscopic structure, conformation, and local and segmental dynamics of pure, strictly monodisperse ring and linear poly(ethylene oxide) (PEO) melts, ranging in molar mass from ∼5300 to ∼20 000 g/mol. The MD results are compared with recent experimental data for the chain center-of-mass self-diffusion coefficient and the normalized single-chain dynamic structure factor obtained from small-angle neutron scattering, neutron spin echo, and pulse-field gradient NMR, and remarkable qualitative and quantitative agreement is observed, despite certain subtle disagreements in important details regarding mainly internal ring motion (loop dynamics). A detailed normal-mode analysis allowed us to check the degree of consistency of ring PEO melt dynamics with the ring Rouse Model and indicated a strong reduction of the normalized mode amplitudes for the smaller mode numbers (compared ...
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description of poly ethylenepropylene confined in nanopores by a modified Rouse Model
Journal of Chemical Physics, 2017Co-Authors: Matthias Muthmann, L Willner, D Richter, Jurgen Allgaier, Margarita Krutyeva, Reiner Zorn, M Ohl, Vivian Rebbin, Peter LindnerAbstract:A recent Model for unentangled polymer chains in confinement [M. Dolgushev and M. Krutyeva, Macromol. Theory Simul. 21, 565 (2012)] is scrutinized by small-angle neutron scattering (SANS) with respect to its static prediction, the single-chain structure factor. We find a remarkable agreement although the Model simplifies the effect of the confinement to a harmonic potential. The effective confinement size from fits of SANS data with the Model agrees well with the actual pore size. Starting from this result we discuss the possibility of an experiment on the dynamic structure factor predicted by the Model. It turns out that such an experiment would need a large ratio polymer dimension/pore size which is difficult but not impossible to achieve.
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dynamics of bimodal polymer melts in the crossover region from Rouse to reptation like behaviour a study with nse spectroscopy
Physica B-condensed Matter, 1997Co-Authors: Silke Rathgeber, A Zirkel, L Willner, D Richter, Annie Brulet, B FaragoAbstract:Abstract The single chain dynamics of bimodal saturated polybutadiene melts is addressed by neutron spin echo spectroscopy. A mode analysis of the structure factor provides an access to different relaxation modes (different spatial extension) separately. For the generalized Rouse Model formulated by Hess an extension from monomodal to bimodal melts is presented.
Ping Tang - One of the best experts on this subject based on the ideXlab platform.
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molecular dynamics simulation of associative polymers understanding linear viscoelasticity from the sticky Rouse Model
Journal of Rheology, 2021Co-Authors: Nuofei Jiang, Hongdong Zhang, Yuliang Yang, Ping TangAbstract:Polymers bearing associative groups (APs) are characterized by their fantastic viscoelastic behaviors. In a work recently published by our group [Jiang et al., Macromolecules 53, 3438–3451 (2020)], a single chain sticky Rouse Model (SRM) is proposed to describe the linear viscoelasticity of APs without the entanglement effect. In this work, equilibrium molecular dynamics simulation of an unentangled melt of an AP with uniformly distributed stickers is carried out, and the dynamic properties are simultaneously analyzed from the SRM. A chain Model with capped stickers is proposed so that a well-defined association chemistry is promised in the simulation system. The relative effective frictional coefficient of stickers, which is the key parameter in the SRM, is extracted from the chain center-of-mass diffusion, and it is found to be consistent with the dynamics of associative reaction in the fully gelated network. Based on this, a linear relaxation modulus and segmental diffusion functions are predicted from the SRM without fitting parameters, and these are found to quantitatively agree with the simulation results, showing the effectiveness of the SRM in connecting the dynamic properties at different molecular levels. The change in relaxation modes and the definition of the effective chain center are found to be crucial in the scenario of the SRM. Finally, the above analysis from the SRM is successfully extended to the simulation system with asymmetric chains. All these simulation results strongly support the SRM as a molecular Model for the linear rheology of AP.
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linear viscoelasticity of associative polymers sticky Rouse Model and the role of bridges
Macromolecules, 2020Co-Authors: Nuofei Jiang, Hongdong Zhang, Ping Tang, Yuliang YangAbstract:Polymers bearing associative groups can exhibit fascinating rheological behaviors. A modified version of the Rouse Model, which is originally used in block copolymers and called the sticky Rouse mo...
