Relaxation behaviors of star polymers in the grid model

2021 ◽  
pp. 2150105
Author(s):  
Xu-Chen Yu ◽  
Ji-Xuan Hou
Keyword(s):  
Diffusion Coefficient ◽  
Relaxation Time ◽  
Star Polymers ◽  
Branch Length ◽  
Linear Polymer ◽  
Star Polymer ◽  
Grid Model ◽  
Dynamical Simulation ◽  
Qualitative Prediction

The tube theory has made a detailed description for the linear polymer entangled system, while the behavior of entangled star polymers is still determined by a qualitative prediction. In this paper, the dynamical simulation of a three-arms star polymer in the grid model is presented. We record the diffusion coefficient [Formula: see text], the relaxation time for the arms of star polymer [Formula: see text] and some other parameters corresponding to different branch length. Therefore, results that are inconsistent with the theoretical begin to emerge.

1H NMR characterisation of the diffusional properties of methanogenic granular sludge

1999 ◽  
Vol 39 (7) ◽  
pp. 187-194 ◽  
Author(s):  
P. Lens ◽  
F. Vergeldt ◽  
G. Lettinga ◽  
H. Van As
Keyword(s):  
Diffusion Coefficient ◽  
Relaxation Time ◽  
Bacterial Cell ◽  
Granular Sludge ◽  
T2 Relaxation ◽  
Self Diffusion ◽  
Diffusion Analysis ◽  
S Matrix ◽  
Granular Matrix ◽  
Pfg Nmr

The diffusive properties of mesophilic methanogenic granular sludge have been studied using diffusion analysis by relaxation time separated pulsed field gradient nuclear magnetic resonance (DARTS PFG NMR) spectroscopy. NMR measurements were performed at 22°C with 10 ml granular sludge at a magnetic field strength of 0.5 T (20 MHz resonance frequency for protons). Spin-spin relaxation (T2) time measurements indicate that three 1H populations can be distinguished in methanogenic granular sludge beds, corresponding to water in three different environments. The T2 relaxation time measurements clearly differentiate the extragranular water (T2 ≈ 1000 ms) from the water present in the granular matrix (T2 = 40-100 ms) and bacterial cell associated water (T2 = 10-15 ms). Self-diffusion coefficient measurements at 22°C of the different 1H-water populations as the tracer show that methanogenic granular sludge does not contain one unique diffusion coefficient. The observed distribution of self-diffusion coefficients varies between 1.1 × 10−9 m2/s (bacterial cell associated water) and 2.1 × 10−9 m2/s (matrix associated water).

Induced polarization and pore radius — A discussion

Geophysics ◽  
2016 ◽  
Vol 81 (5) ◽  
pp. D519-D526 ◽  
Author(s):  
Andreas Weller ◽  
Zeyu Zhang ◽  
Lee Slater ◽  
Sabine Kruschwitz ◽  
Matthias Halisch
Keyword(s):  
Diffusion Coefficient ◽  
Relaxation Time ◽  
Diffusion Coefficients ◽  
Pore Radius ◽  
Mercury Porosimetry ◽  
Induced Polarization ◽  
Reliable Estimate ◽  
Characteristic Relaxation Time ◽  
A Value ◽  
Apparent Diffusion

Permeability estimation from induced polarization (IP) measurements is based on a fundamental premise that the characteristic relaxation time [Formula: see text] is related to the effective hydraulic radius [Formula: see text] controlling fluid flow. The approach requires a reliable estimate of the diffusion coefficient of the ions in the electrical double layer. Others have assumed a value for the diffusion coefficient, or postulated different values for clay versus clay-free rocks. We have examined the link between a widely used single estimate of [Formula: see text] and [Formula: see text] for an extensive database of sandstone samples, in which mercury porosimetry data confirm that [Formula: see text] is reliably determined from a modification of the Hagen-Poiseuille equation assuming that the electrical tortuosity is equal to the hydraulic tortuosity. Our database does not support the existence of one or two distinct representative diffusion coefficients but instead demonstrates strong evidence for six orders of magnitude of variation in an apparent diffusion coefficient that is well-correlated with [Formula: see text] and the specific surface area per unit pore volume [Formula: see text]. Two scenarios can explain our findings: (1) the length scale defined by [Formula: see text] is not equal to [Formula: see text] and is likely much longer due to the control of pore-surface roughness or (2) the range of diffusion coefficients is large and likely determined by the relative proportions of the different minerals (e.g., silica and clays) making up the rock. In either case, the estimation of [Formula: see text] (and hence permeability) is inherently uncertain from a single characteristic IP relaxation time as considered in this study.

Changes in the apparent diffusion coefficient of water and T2 relaxation time in gerbil hippocampus after mild ischemia

Neuroreport ◽  
2000 ◽  
Vol 11 (15) ◽  
pp. 3333-3336 ◽  
Author(s):  
Lidong Zhu ◽  
Nobuhito Saito ◽  
Osamu Abe ◽  
Toshiyuki Okubo ◽  
Haruyasu Yamada ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Relaxation Time ◽  
Apparent Diffusion Coefficient ◽  
T2 Relaxation Time ◽  
T2 Relaxation ◽  
Apparent Diffusion

scholarly journals Swap-Driven Self-Adhesion and Healing of Vitrimers

Coatings ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 114 ◽  
Author(s):  
Simone Ciarella ◽  
Wouter Ellenbroek
Keyword(s):  
Molecular Dynamics ◽  
Relaxation Time ◽  
Stress Relaxation ◽  
Healing Process ◽  
Star Polymers ◽  
Coarse Grained ◽  
Self Healing ◽  
Central Question ◽  
Trade Off ◽  
Dynamics Simulations

Vitrimers are covalent network materials, comparable in structure to classical thermosets. Unlike normal thermosets, they possess a chemical bond swap mechanism that makes their structure dynamic and suitable for activated welding and even autonomous self-healing. The central question in designing such materials is the trade-off between autonomy and material stability: the swap mechanism facilitates the healing, but it also facilitates creep, which makes the perfectly stable self-healing solid a hard goal to reach. Here, we address this question for the case of self-healing vitrimers made from star polymers. Using coarse-grained molecular dynamics simulations, we studied the adhesion of two vitrimer samples and found that they bond together on timescales that are much shorter than the stress relaxation time. We showed that the swap mechanism allows the star polymers to diffuse through the material through coordinated swap events, but the healing process is much faster and does not depend on this mobility.

A well-defined coil–comb polycationic brush with “star polymers” as side chains for gene delivery

2014 ◽  
Vol 5 (16) ◽  
pp. 4670-4678 ◽  
Author(s):  
Mingming Zhang ◽  
Qingqing Xiong ◽  
Yinsong Wang ◽  
Zhibao Zhang ◽  
Wei Shen ◽  
...  
Keyword(s):  
Gene Delivery ◽  
Star Polymers ◽  
Star Polymer ◽  
Side Chains ◽  
Single Star ◽  
Grafting Density

The well-defined polycationic brush with super-high grafting density of PDMAEMA showed higher transfection capability than the single star polymer and PEI25K.

Evaluating the Effect of Termination by Chain - Chain Coupling in Living Free-Radical Polymerizations

2003 ◽  
Vol 56 (8) ◽  
pp. 775 ◽  
Author(s):  
Jeffrey Pyun ◽  
Ian Rees ◽  
Jean M. J. Fréchet ◽  
Craig J. Hawker
Keyword(s):  
Free Radical ◽  
Star Polymers ◽  
Star Polymer ◽  
Direct Result ◽  
Vinyl Monomers ◽  
Linear Polymers ◽  
Radical Coupling ◽  
Novel Approach ◽  
Vis Spectroscopy ◽  
Radical Polymerizations

A novel approach based on the reaction of multifunctional star polymers with chromophore-labelled linear polymers is presented for evaluating the extent of termination by chain–chain coupling during living free-radical polymerizations. A mixed initiating system consisting of an unlabelled, multifunctional initiator and an excess of a monofunctional alkoxyamine initiator containing a chromophore, such as pyrene, is used to initiate the living polymerization of vinyl monomers leading to a mixture of star and linear polymers. The occurrence of chain–chain coupling is readily identified and quantified by isolating the star polymer that is obtained and elucidating the level of incorporation of pyrene units by UV/vis spectroscopy. This allows the level of chain–chain coupling to be determined since the inclusion of pyrene into the star structure is a direct result of termination by radical coupling.

scholarly journals Diffusional Properties of Methanogenic Granular Sludge: 1H NMR Characterization

2003 ◽  
Vol 69 (11) ◽  
pp. 6644-6649 ◽  
Author(s):  
Piet N. L. Lens ◽  
Rakel Gastesi ◽  
Frank Vergeldt ◽  
Adriaan C. van Aelst ◽  
Antonio G. Pisabarro ◽  
...  
Keyword(s):  
Diffusion Coefficient ◽  
Relaxation Time ◽  
Nmr Spectroscopy ◽  
Diffusion Coefficients ◽  
Metal Sulfide ◽  
Free Water ◽  
Granular Sludge ◽  
Self Diffusion ◽  
Nmr Characterization ◽  
Self Diffusion Coefficient

ABSTRACT The diffusive properties of anaerobic methanogenic and sulfidogenic aggregates present in wastewater treatment bioreactors were studied using diffusion analysis by relaxation time-separated pulsed-field gradient nuclear magnetic resonance (NMR) spectroscopy and NMR imaging. NMR spectroscopy measurements were performed at 22°C with 10 ml of granular sludge at a magnetic field strength of 0.5 T (20 MHz resonance frequency for protons). Self-diffusion coefficients of H2O in the investigated series of mesophilic aggregates were found to be 51 to 78% lower than the self-diffusion coefficient of free water. Interestingly, self-diffusion coefficients of H2O were independent of the aggregate size for the size fractions investigated. Diffusional transport occurred faster in aggregates growing under nutrient-rich conditions (e.g., the bottom of a reactor) or at high (55°C) temperatures than in aggregates cultivated in nutrient-poor conditions or at low (10°C) temperatures. Exposure of aggregates to 2.5% glutaraldehyde or heat (70 or 90°C for 30 min) modified the diffusional transport up to 20%. In contrast, deactivation of aggregates by HgCl2 did not affect the H2O self-diffusion coefficient in aggregates. Analysis of NMR images of a single aggregate shows that methanogenic aggregates possess a spin-spin relaxation time and self-diffusion coefficient distribution, which are due to both physical (porosity) and chemical (metal sulfide precipitates) factors.

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