Primitive chain network simulations of probe rheology

Soft Matter ◽  
2017 ◽  
Vol 13 (37) ◽  
pp. 6585-6593 ◽  
Author(s):  
Yuichi Masubuchi ◽  
Yoshifumi Amamoto ◽  
Ankita Pandey ◽  
Cheng-Yang Liu
Keyword(s):  
Relaxation Time ◽  
Viscoelastic Relaxation ◽  
Network Simulations ◽  
Cross Correlations

The dynamics of probe chains immersed in immobile matrices was examined via the multi-chain slip-link simulation. The viscoelastic relaxation time was fairly reproduced, whereas the relaxation intensity was underestimated, possibly due to flaws in the orientational cross-correlations between the probe and the matrices.

scholarly journals A Distinguishable Role of eDNA in the Viscoelastic Relaxation of Biofilms

mBio ◽  
2013 ◽  
Vol 4 (5) ◽  
Author(s):  
Brandon W. Peterson ◽  
Henny C. van der Mei ◽  
Jelmer Sjollema ◽  
Henk J. Busscher ◽  
Prashant K. Sharma
Keyword(s):  
Relaxation Time ◽  
Stress Relaxation ◽  
Time Constant ◽  
Extracellular Polymeric Substances ◽  
Principal Component ◽  
Mechanical Stresses ◽  
Extracellular Dna ◽  
Viscoelastic Relaxation ◽  
Content Type ◽  
Relaxation Time Constants

ABSTRACTBacteria in the biofilm mode of growth are protected against chemical and mechanical stresses. Biofilms are composed, for the most part, of extracellular polymeric substances (EPSs). The extracellular matrix is composed of different chemical constituents, such as proteins, polysaccharides, and extracellular DNA (eDNA). Here we aimed to identify the roles of different matrix constituents in the viscoelastic response of biofilms.Staphylococcus aureus,Staphylococcus epidermidis,Streptococcus mutans, andPseudomonas aeruginosabiofilms were grown under different conditions yielding distinct matrix chemistries. Next, biofilms were subjected to mechanical deformation and stress relaxation was monitored over time. A Maxwell model possessing an average of four elements for an individual biofilm was used to fit the data. Maxwell elements were defined by a relaxation time constant and their relative importance. Relaxation time constants varied widely over the 104 biofilms included and were divided into seven ranges (<1, 1 to 5, 5 to 10, 10 to 50, 50 to 100, 100 to 500, and >500 s). Principal-component analysis was carried out to eliminate related time constant ranges, yielding three principal components that could be related to the known matrix chemistries. The fastest relaxation component (<3 s) was due to the presence of water and soluble polysaccharides, combined with the absence of bacteria, i.e., the heaviest masses in a biofilm. An intermediate component (3 to 70 s) was related to other EPSs, while a distinguishable role was assigned to intact eDNA, which possesses a unique principal component with a time constant range (10 to 25 s) between those of EPS constituents. This implies that eDNA modulates its interaction with other matrix constituents to control its contribution to viscoelastic relaxation under mechanical stress.IMPORTANCEThe protection offered by biofilms to organisms that inhabit it against chemical and mechanical stresses is due in part to its matrix of extracellular polymeric substances (EPSs) in which biofilm organisms embed themselves. Mechanical stresses lead to deformation and possible detachment of biofilm organisms, and hence, rearrangement processes occur in a biofilm to relieve it from these stresses. Maxwell analysis of stress relaxation allows the determination of characteristic relaxation time constants, but the biofilm components and matrix constituents associated with different stress relaxation processes have never been identified. Here we grew biofilms with different matrix constituents and used principal-component analysis to reveal that the presence of water and soluble polysaccharides, together with the absence of bacteria, is associated with the fastest relaxation, while other EPSs control a second, slower relaxation. Extracellular DNA, as a matrix constituent, had a distinguishable role with its own unique principal component in stress relaxation with a time constant range between those of other EPSs.

scholarly journals Studies on dielectric relaxation in relation to viscosity of some anilines, phenol, and their binary mixtures at microwave frequencies

2019 ◽  
Vol 97 (2) ◽  
pp. 210-215
Author(s):  
C.V. Maridevarmath ◽  
G.H. Malimath
Keyword(s):  
Relaxation Time ◽  
Steady State ◽  
Dynamic Viscosity ◽  
Room Temperature ◽  
Viscoelastic Model ◽  
Frictional Resistance ◽  
Nonlinear Behaviour ◽  
Viscoelastic Relaxation ◽  
Microwave Frequencies ◽  
Loss Formula

In the present work, the study of variation of relaxation time (τ) with viscosity of the medium (η) is carried out on four polar samples: 2-Nitroaniline, 4-Bromoaniline, 4-Chloroaniline, 4-Chlorophenol, and also on the binary mixture of 2-Nitroaniline + 4-Bromoaniline at room temperature by using microwave bench operating at a frequency of 9.59 GHz. In this regard, the different parameters like dielectric constant ([Formula: see text]), dielectric loss ([Formula: see text]), relaxation time (τs), macroscopic steady state viscosity (ηs), dynamic viscosity (ηd), and viscoelastic relaxation time (τve) were determined for all the systems. It is observed that the relaxation time (τs) increases with the increase in the viscosity of the medium for all the systems. Plots of log(τs) versus log(ηs) for all the systems show that variation of relaxation time is found to be nonlinear in the higher viscosity regions. This suggests the failure of Debye’s theory at these regions. Further, the nonlinear behaviour of relaxation time with the viscosity is explained by using the viscoelastic model suggested by Barlow et al. (Proc. R. Soc. A 309, 473 (1969). doi: 10.1098/rspa.1969.0053 ). It is also observed that macroscopic steady state viscosity (ηs) values are greater than the dynamic viscosity (ηd), and viscoelastic relaxation time (τve) values were found to be lower compared to the relaxation time (τs). These results suggest that the effective frictional resistance experienced by the molecules during reorientation is lower and the measured values of macroscopic steady state viscosity (ηs) are frequency dependent.

Orientational cross correlations between entangled branch polymers in primitive chain network simulations

2017 ◽  
Vol 147 (18) ◽  
pp. 184903 ◽  
Author(s):  
Yuichi Masubuchi ◽  
Ankita Pandey ◽  
Yoshifumi Amamoto ◽  
Takashi Uneyama
Keyword(s):  
Network Simulations ◽  
Cross Correlations

scholarly journals Recovery of Shear-Modified Polybutadiene Solutions

2006 ◽  
Vol 79 (2) ◽  
pp. 267-280 ◽  
Author(s):  
C. M. Roland ◽  
C. G. Robertson
Keyword(s):  
Relaxation Time ◽  
Dynamic Modulus ◽  
Viscoelastic Relaxation ◽  
Newtonian Viscosity ◽  
Low Viscosity ◽  
Stress Coefficient ◽  
Linear Viscoelastic ◽  
Recoverable Compliance ◽  
Transient Viscosity ◽  
Nonlinear Shear

Abstract We have investigated the recovery of the overshoot in the transient viscosity, the first normal stress coefficient, and the dynamic modulus for entangled polybutadiene solutions subjected to nonlinear shear flow. The molecular-weight dependences of the various time scales (linear viscoelastic relaxation time, entanglement recovery time, and timescale for decay of stress following cessation of shearing) are all consistent with the usual 3.4 power law. Nevertheless, the time for recovery of the stress overshoot and plateau value of the dynamic modulus were substantially longer (by as much as two orders of magnitude) than the linear viscoelastic relaxation time calculated from the Newtonian viscosity and the equilibrium recoverable compliance. These results indicate that complete entanglement recovery requires cooperative chain motions over a length scale exceeding that associated with linear relaxation. This persistence of a disentangled state means that a state of low viscosity and reduced elasticity is retained for an extended time, suggesting that shear modification can be used to facilitate the processing of polymers.

Electrostatically Driven Creep in Viscoelastic Dielectric Elastomers

2013 ◽  
Vol 81 (5) ◽  
Author(s):  
Jin Wang ◽  
Thao D. Nguyen ◽  
Harold S. Park
Keyword(s):  
Finite Element ◽  
Relaxation Time ◽  
Element Model ◽  
Constitutive Law ◽  
Dielectric Elastomers ◽  
Inhomogeneous Deformation ◽  
Viscoelastic Relaxation ◽  
Constant Voltage ◽  
Dynamic Finite Element ◽  
Electromechanical Instability

We utilize a nonlinear, dynamic finite element model coupled with a finite deformation viscoelastic constitutive law to study the inhomogeneous deformation and instabilities resulting from the application of a constant voltage to dielectric elastomers. The constant voltage loading is used to study electrostatically driven creep and the resulting electromechanical instabilities for two different cases that have all been experimentally observed, i.e., electromechanical snap-through instability and bursting drops in a dielectric elastomer. We find that in general, increasing the viscoelastic relaxation time leads to an increase in time needed to nucleate the electromechanical instability. However, we find for these two cases that the time needed to nucleate the instability scales with the relaxation time.

Cooperative Domain Model for Yield Phenomenon

1990 ◽  
Vol 215 ◽  
Author(s):  
S. Matsuoka
Keyword(s):  
Relaxation Time ◽  
Strain Rate ◽  
Yield Stress ◽  
Molecular Model ◽  
Configurational Entropy ◽  
Domain Model ◽  
Characteristic Relaxation Time ◽  
Viscoelastic Relaxation ◽  
Classical Plasticity ◽  
Linear Viscoelastic

AbstractA molecular model for cooperative segmental relaxation has been proposed, which leads to the Adam-Gibbs type dependence of the characteristic relaxation time on temperature and the configurational entropy. When the size distribution for the cooperative domains is introduced, the resulting relaxation spectrum is similar to the Kohlrausch-Williams-Watts (KWW) equation in the frequency range near the loss maximum, but the fit is actually better in the high frequency extremes where the KWW equation always underpredicts the intensity. The model also predicts the broad spread of the spectrum in the non-equilibrium state from the distribution of the apparent activation energy arising from the different sizes of domains.We now extend this model to the yield phenomenon in glassy polymers. Under the stress, a domain has two alternatives to dissipate the strain energy. One way is to relieve the stress at the rate dictated by the linear viscoelastic relaxation time. This process is possible only when the strain rate is low. At above a certain strain rate, the stress reaches the strength of the domain, forcing to irreversibly break up the domain structure in the manner that can be described by the classical plasticity. It can be shown that the yield stress of a real polymer is a combination of the above two types of stresses. Namely, at a given strain rate, the small domains with short relaxation time will attain the linear viscoelastic steady stress while the larger domains reach the (limiting) plastic yield stress. Thus, the strain rate dependence of yield stress can be predicted from the linear viscoelastic relaxation spectra, even though the yield phenomenon is clearly in the realm of nonlinear viscoelasticity.

Spatial Distribution of Viscoelastic Relaxation Following a Subduction Earthquake

2020 ◽  
Author(s):  
Yuting Ji ◽  
Wenke Sun ◽  
He Tang
Keyword(s):  
Spatial Distribution ◽  
Relaxation Time ◽  
Sea Water ◽  
Characteristic Relaxation Time ◽  
Viscoelastic Relaxation ◽  
Gravity Field Model ◽  
Viscoelastic Characteristic ◽  
Gravity Changes ◽  
2004 Sumatra Earthquake ◽  
Seismic Deformation

&lt;p&gt;Viscoelastic relaxation is generally considered as the dominant process of the long-term post-seismic deformation, while viscoelastic characteristic relaxation time represents the time scale of deformation caused by viscoelastic relaxation effect after the earthquake. The subduction earthquakes which occurred at the boundary of the ocean and continental plates often release greater stress, and the stress relaxation of mantle materials is more significant due to the response to viscoelasticity. Satellite gravity mission GRACE (gravity recovery and climate experience) is able to observe the corresponding co-seismic and post-seismic gravity changes. Therefore, in this study, we use the monthly gravity field model data of GRACE RL06 to study the post-seismic gravity changes of 2011 Tohoku earthquake and 2004 Sumatra earthquake. After removing the influence of sea level changes, GIA changes and GLDAS on the seasonal precipitation changes in the land area, as well as the sea water correction, we get the post-seismic deformation only related to the deformation of the solid earth. Then we use the attenuation function to fit each grid value and obtain the spatial distribution of viscoelastic characteristic relaxation time after rejecting the afterslip from the total post-seismic deformation. Thus&amp;#65292;we can capture &amp;#160;the viscous structure in the subduction area.&lt;/p&gt;

Comments on “Mechanical relaxation time scales in a Zr-Ti-Ni-Cu-Be bulk metallic glass” by Daewoong Suh and Reinhold H. Dauskardt [J. Mater. Res. 17, 1254 (2002)]

2003 ◽  
Vol 18 (8) ◽  
pp. 1998-1999 ◽  
Author(s):  
K. Schröter
Keyword(s):  
Relaxation Time ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Stress Relaxation ◽  
Metallic Glass ◽  
Bulk Metallic Glass ◽  
Time Scales ◽  
Mechanical Relaxation ◽  
Viscoelastic Relaxation

The stress relaxation results below the glass-transition temperatureTgare a continuation of the viscoelastic relaxation aboveTg. This means that the dynamic glass transition and not a secondary relaxation is the reason for the observed effects.

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