Reinforcement Mechanisms in Carbon Black and Silica Loaded Rubber Melts at Low Stresses

1996 ◽  
Vol 69 (2) ◽  
pp. 253-265 ◽  
Author(s):  
H. Eggers ◽  
P. Schummer
Keyword(s):  
Relaxation Times ◽  
Polymer Structure ◽  
Rubber Matrix ◽  
Dynamic Moduli ◽  
Effectiveness Factors ◽  
Constant Height ◽  
Linear Viscoelastic ◽  
Hydrodynamic Effects ◽  
Very High ◽  
Thomas Equation

Abstract For a range of different fillers, silicas and carbon blacks, added to a rubber melt at various concentrations, dynamic moduli in the linear viscoelastic limit have been determined. It is shown that reinforcement is due to hydrodynamic effects and the formation of a secondary particulate structure within the rubber matrix. Both mechanisms can be distinguished experimentally by a frequency sweep. Hydrodynamic reinforcement depends on the filler volume to which immobilized polymer must be added. Its concentration dependence is well described by the semiempirical exponential Thomas Equation. Nominal and effective filler loadings are related by concentration-independent effectiveness factors which can be modelled for all types of fillers considering an immobilized layer of constant height around an agglomerated cluster of filler particles. This provides an explanation for the well-known dependence of reinforcement ability on surface area at small stresses. The chemical and microscopic structure of the filler surface appears to be less important with respect to immobilization ability in the linear viscoelasic regime. The secondary structure formed by the particles is found to be tied together by the elastomer. Its modulus correlates with the filler's immobilization ability and shows little dependence on the filler nature. Due to formation of a filler-polymer structure with individual relaxation times, a strict separability of hydrodynamic and interparticular-reinforcement mechanisms at very high loadings no longer applies.

A non-linear viscoelastic model with structure-dependent relaxation times

1976 ◽  
Vol 1 (2) ◽  
pp. 147-157 ◽  
Author(s):  
D. Acierno ◽  
F.P. La Mantia ◽  
G. Marrucci ◽  
G. Rizzo ◽  
G. Titomanlio
Keyword(s):  
Relaxation Times ◽  
Viscoelastic Model ◽  
Non Linear ◽  
Linear Viscoelastic ◽  
Linear Viscoelastic Model

The Measurement of the Apparent Nuclear Spin-Spin Relaxation Times of N.Q.R. Signals in the Very-High-Frequency Region

1979 ◽  
Vol 32 (2) ◽  
pp. 243 ◽  
Author(s):  
PJ Bryant ◽  
S Hacobian
Keyword(s):  
Crystal Field ◽  
Spin Relaxation ◽  
Nuclear Spin ◽  
High Frequency ◽  
Relaxation Times ◽  
Frequency Region ◽  
Very High Frequency ◽  
High Frequency Region ◽  
Pulse Detection ◽  
Very High

The Doolan-Hacobian n.q.r. double pulse detection technique is described for the measurement of n.q.r, apparent spin-spin relaxation times as applied to a v.h.f. lecher line super-regenerative spectrometer. Results are presented for the linewidths of the 79Br and 81Br resonances in p-dibromobenzene. It was found that crystal-field inhomogeneities produce significant broadening of the n.q.r. signal.

scholarly journals Ratio of dynamic moduli and estimation of relaxation times

2002 ◽  
Vol 46 (4) ◽  
pp. 777 ◽  
Author(s):  
Jianhua Huang ◽  
Donald G. Baird
Keyword(s):  
Relaxation Times ◽  
Dynamic Moduli

Theory of vibrational relaxation in mixtures of ortho- and para-hydrogen

1981 ◽  
Vol 59 (8) ◽  
pp. 1277-1283 ◽  
Author(s):  
Avygdor Moise ◽  
Huw O. Pritchard
Keyword(s):  
Rate Constants ◽  
Vibrational Relaxation ◽  
Numerical Study ◽  
Relaxation Times ◽  
High Dilutions ◽  
State Rate ◽  
The Mean ◽  
The Individual ◽  
Individual Rate ◽  
Very High

A numerical study of the vibrational relaxation at 500 K of a mixture of ortho-H2 and para-H2 is described. The required state-to-state rate constants were calculated from the quantum results of Rabitz and co-workers, and missing pieces of data were estimated by interpolation.It is concluded that only one relaxation time will be observed in any mixture of ortho-H2 and para-H2 and that (except at very high dilutions in a third inert gas) the relaxation rate constant will be close to the mean of the individual rate constants for relaxation, weighted according to the respective mole fractions of ortho-H2 and para-H2 present in the mixture.We find that the relaxation process can be modelled very accurately as an electrical RC network, whose time constants can be written down quite easily as sums of the appropriate microscopic rate constants, and by using this model, it is a simple matter to explore the conditions required for a mixture of two gases to exhibit two distinct vibrational relaxation times.

scholarly journals Spatiotemporal organization of chromatin domains: role of interaction energy and polymer entropy

2021 ◽  
Author(s):  
Kiran Kumari ◽  
J. Ravi Prakash ◽  
Ranjith Padinhateeri
Keyword(s):  
Interaction Energy ◽  
Relaxation Times ◽  
Interaction Strength ◽  
Strong Interactions ◽  
Loop Formation ◽  
Chromatin Domains ◽  
Distance Distributions ◽  
Spatio Temporal ◽  
Multiple Domains ◽  
Hydrodynamic Effects

Chromatin is known to be organised into multiple domains of varying sizes and compaction. While these domains are often imagined as static structures, they are highly dynamic and show cell-to-cell variability. Since processes such as gene regulation and DNA replication occur in the context of these domains, it is important to understand their organization, fluctuation and dynamics. To simulate chromatin domains, one requires knowledge of interaction strengths among chromatin segments. Here, we derive interaction strength parameters from experimentally known contact maps, and use it to predict chromatin organization and dynamics. Taking α-globin domain as an example, we investigate its 3D organization, size/shape fluctuations, and dynamics of different segments within a domain, accounting for hydrodynamic effects. Perturbing the interaction strengths systematically, we quantify how epigenetic changes can alter the spatio-temporal nature of the domains. Computing distance-distributions and relaxation times for different chromatin states, we show that weak and strong interactions cooperatively determine the organization of the domains and how the solid-like and liquid-like nature of chromatin gets altered as we vary epigenetic states. Quantifying dynamics of chromatin segments within a domain, we show how the competition between polymer entropy and interaction energy influence the timescales of loop formation and maintenance of stable loops.PACS numbers:

scholarly journals Estimation of the Dynamic Moduli of Viscoelastic Asphalt Mixtures Using the Extended Kalman Filter Algorithm

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Yu-Seok Gong ◽  
Dowan Kim ◽  
Sungho Mun
Keyword(s):  
Kalman Filter ◽  
Extended Kalman Filter ◽  
Master Curves ◽  
Dynamic Moduli ◽  
Frequency Sweep ◽  
Sigmoidal Curve ◽  
Linear Viscoelastic ◽  
Kalman Filter Algorithm ◽  
Impact Resonance ◽  
Mean Square Errors

Here, we develop a model predicting the dynamic moduli of hot-mix asphalt/concrete using the extended Kalman filter (EKF) algorithm and draw frequency-domain master curves. Discrete dynamic moduli were obtained via impact resonance tests (IRTs) on linear viscoelastic (LVE) asphalt at 20, 30, 35, 40, and 50°C. Typically, viscoelastic characteristics have been used to derive asphalt dynamic moduli; compressive frequency sweep tests at different frequencies (Hz) and temperatures are employed to this end. We compared IRT-derived viscoelastic master curves obtained via compressive frequency sweep testing to those derived using the EKF algorithm, which employs a nonlinear sigmoidal curve and a Taylor series to explore the viscoelastic function. The model reduced errors at both low and high frequencies by correcting the coefficients of the master curve. Furthermore, the predictive model effectively estimated dynamic moduli at various frequencies, and also root-mean-square errors (RMSEs) which, together with the mean percentage errors (MPEs), were used to compare predictions.

Preparation and Characterization of Dielectric Behavior of A2/3Cu3Ti4O12 (A = Nd, Sm, Gd, Dy) Ceramics

2010 ◽  
Vol 67 ◽  
pp. 28-33 ◽  
Author(s):  
Dorota Szwagierczak ◽  
Jan Kulawik
Keyword(s):  
Single Phase ◽  
Elevated Temperatures ◽  
Relaxation Times ◽  
Dielectric Behavior ◽  
X Ray Diffraction ◽  
Conventional Solid State Reaction ◽  
Low Frequencies ◽  
Perovskite Materials ◽  
Very High

In this work perovskite materials A2/3Cu3Ti4O12 (where A=Nd, Sm, Gd, Dy) were synthesized by conventional solid state reaction and sintered at 1000-1100°C. X-ray diffraction analysis confirmed single-phase composition of the investigated ceramics. Dielectric properties of the samples were investigated in the temperature range from -55 to 300°C at frequencies 10 Hz – 2 MHz. Dielectric permittivities of the ceramics are very high, exceeding 105 at low frequencies and/or elevated temperatures (above 50°C) and 103 at higher frequencies and/or low temperatures. Two observed contributions to the dielectric response are attributed to semiconducting grains and more resistive grain boundaries. For Nd2/3Cu3Ti4O12 and Sm2/3Cu3Ti4O12 ceramics, the observed low- and high frequency plateaus are lower than those for Gd2/3Cu3Ti4O12 and Dy2/3Cu3Ti4O12. The relaxation times determined on the basis of impedance data were found to decrease with increasing atomic number of lanthanide. The analysis of the impedance spectroscopic data and the microstructure implies spontaneous formation of internal barrier layer capacitors in the investigated materials.

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