scholarly journals Assessment of the Tumbling-Snake Model against Linear and Nonlinear Rheological Data of Bidisperse Polymer Blends

Polymers ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 376 ◽  
Author(s):  
Pavlos Stephanou ◽  
Martin Kröger
Keyword(s):  
Brownian Dynamics ◽  
Stationary Solutions ◽  
Model Parameters ◽  
Snake Model ◽  
Shear Rates ◽  
Rheological Data ◽  
Wide Range ◽  
Dynamics Simulations ◽  
Brownian Dynamics Simulations ◽  
Entangled Melts

We have recently solved the tumbling-snake model for concentrated polymer solutions and entangled melts in the academic case of a monodisperse sample. Here, we extend these studies and provide the stationary solutions of the tumbling-snake model both analytically, for small shear rates, and via Brownian dynamics simulations, for a bidisperse sample over a wide range of shear rates and model parameters. We further show that the tumbling-snake model bears the necessary capacity to compare well with available linear and non-linear rheological data for bidisperse systems. This capacity is added to the already documented ability of the model to accurately predict the shear rheology of monodisperse systems.

scholarly journals Tumbling-Snake Model for Polymeric Liquids Subjected to Biaxial Elongational Flows with a Focus on Planar Elongation

2018 ◽  
Author(s):  
Pavlos S. Stephanou ◽  
Martin Kröger
Keyword(s):  
Steady State ◽  
Brownian Dynamics ◽  
Elongational Flow ◽  
Stationary Solutions ◽  
Recent Experimental Data ◽  
Model Parameters ◽  
Snake Model ◽  
Wide Range ◽  
Elongational Flows ◽  
Dynamics Simulations

We have recently solved the tumbling-snake model for concentrated polymer solutions and entangled melts in the presence of both steady-state and transient shear and uniaxial elongational flows, supplemented by a variable link tension coefficient. Here, we provide the transient and stationary solutions of the tumbling-snake model under biaxial elongation both analytically, for small and large elongation rates, and via Brownian dynamics simulations, for the case of planar elongational flow over a wide range of rates, times, and the model parameters. We show that both the steady-state and transient first planar viscosity predictions are similar to their uniaxial counterparts, in accord with recent experimental data. The second planar viscosity seems to behave in all aspects similarly to the shear viscosity, if shear rate is replaced by elongation rate.

scholarly journals A multiscale approach for computing gated ligand binding from molecular dynamics and Brownian dynamics simulations

2021 ◽  
Author(s):  
S. Kashif Sadiq ◽  
Abraham Muñiz Chicharro ◽  
Patrick Friedrich ◽  
Rebecca C. Wade
Keyword(s):  
Molecular Dynamics ◽  
Ligand Binding ◽  
Rate Constants ◽  
Brownian Dynamics ◽  
Multiscale Approach ◽  
Wide Range ◽  
Conformational Gating ◽  
Dynamics Simulations ◽  
Brownian Dynamics Simulations ◽  
Hiv 1

We develop an approach to characterise the effects of gating by a multi-conformation protein consisting of macrostate conformations that are either accessible or inaccessible to ligand binding. We first construct a Markov state model of the apo-protein from atomistic molecular dynamics simulations from which we identify macrostates and their conformations, compute their relative macrostate populations and interchange kinetics, and structurally characterise them in terms of ligand accessibility. We insert the calculated first-order rate constants for conformational transitions into a multi-state gating theory from which we derive a gating factor γ that quantifies the degree of conformational gating. Applied to HIV-1 protease, our approach yields a kinetic network of three accessible (semi-open, open and wide-open) and two inaccessible (closed and a newly identified, `parted') macrostate conformations. The `parted' conformation sterically partitions the active site, suggesting a possible role in product release. We find that the binding kinetics of drugs and drug-like inhibitors to HIV-1 protease falls in the slow gating regime. However, because γ=0.75, conformational gating only modestly slows ligand binding. Brownian dynamics simulations of the diffusional association of eight inhibitors to the protease - that have a wide range of experimental association constants (~104 - 1010 M-1s-1) - yields gated rate constants in the range ~0.5-5.7 × 108 M-1s-1. This indicates that, whereas the association rate of some inhibitors is described by the model, for most inhibitors the subsequent induced fit step leads to slower association rates. For systems known to be modulated by conformational gating, the approach could be scaled computationally efficiently to screen association kinetics for a large number of ligands.

scholarly journals Modelling a hydrodynamic instability in freely settling colloidal gels

2018 ◽  
Vol 856 ◽  
pp. 1014-1044 ◽  
Author(s):  
Zsigmond Varga ◽  
Jennifer L. Hofmann ◽  
James W. Swan
Keyword(s):  
Brownian Dynamics ◽  
Fine Particles ◽  
Hydrodynamic Instability ◽  
State Diagram ◽  
Colloidal Dispersions ◽  
Experimental Systems ◽  
Wide Range ◽  
Network Weight ◽  
Dynamics Simulations ◽  
Brownian Dynamics Simulations

Attractive colloidal dispersions, suspensions of fine particles which aggregate and frequently form a space-spanning elastic gel are ubiquitous materials in society with a wide range of applications. The colloidal networks in these materials can exist in a mode of free settling when the network weight exceeds its compressive yield stress. An equivalent state occurs when the network is held fixed in place and used as a filter through which the suspending fluid is pumped. In either scenario, hydrodynamic instabilities leading to loss of network integrity occur. Experimental observations have shown that the loss of integrity is associated with the formation of eroded channels, so-called streamers, through which the fluid flows rapidly. However, the dynamics of growth and subsequent mechanism of collapse remain poorly understood. Here, a phenomenological model is presented that describes dynamically the radial growth of a streamer due to erosion of the network by rapid fluid back flow. The model exhibits a finite-time blowup – the onset of catastrophic failure in the gel – due to activated breaking of the inter-colloid bonds. Brownian dynamics simulations of hydrodynamically interacting and settling colloids in dilute gels are employed to examine the initiation and propagation of this instability, which are in good agreement with the theory. The model dynamics is also shown to accurately replicate measurements of streamer growth in two different experimental systems. The predictive capabilities and future improvements of the model are discussed and a stability-state diagram is presented providing insight into engineering strategies for avoiding settling instabilities in networks meant to have long shelf lives.

scholarly journals Structure evolution of suspensions under time-dependent electric or magnetic field

2021 ◽  
Author(s):  
Konstantinos Manikas ◽  
Markus Hütter ◽  
Patrick D. Anderson
Keyword(s):  
Magnetic Field ◽  
Field Strength ◽  
Brownian Dynamics ◽  
Thermal Fluctuations ◽  
Time Dependent ◽  
Structure Evolution ◽  
Strength Increase ◽  
Large Rotation ◽  
Dynamics Simulations ◽  
Brownian Dynamics Simulations

AbstractThe effect of time-dependent external fields on the structures formed by particles with induced dipoles dispersed in a viscous fluid is investigated by means of Brownian Dynamics simulations. The physical effects accounted for are thermal fluctuations, dipole-dipole and excluded volume interactions. The emerging structures are characterised in terms of particle clusters (orientation, size, anisotropy and percolation) and network structure. The strength of the external field is increased in one direction and then kept constant for a certain amount of time, with the structure formation being influenced by the slope of the field-strength increase. This effect can be partially rationalized by inhomogeneous time re-scaling with respect to the field strength, however, the presence of thermal fluctuations makes the scaling at low field strength inappropriate. After the re-scaling, one can observe that the lower the slope of the field increase, the more network-like and the thicker the structure is. In the second part of the study the field is also rotated instantaneously by a certain angle, and the effect of this transition on the structure is studied. For small rotation angles ($$\theta \le 20^{{\circ }}$$ θ ≤ 20 ∘ ) the clusters rotate but stay largely intact, while for large rotation angles ($$\theta \ge 80^{{\circ }}$$ θ ≥ 80 ∘ ) the structure disintegrates and then reforms, due to the nature of the interactions (parallel dipoles with perpendicular inter-particle vector repel each other). For intermediate angles ($$20<\theta <80^{{\circ }}$$ 20 < θ < 80 ∘ ), it seems that, during rotation, the structure is altered towards a more network-like state, as a result of cluster fusion (larger clusters). The details provided in this paper concern an electric field, however, all results can be projected into the case of a magnetic field and paramagnetic particles.

scholarly journals Influence of size polydispersity on magnetic field tunable structures in magnetic nanofluids containing superparamagnetic nanoparticles.

2021 ◽  
Author(s):  
Dillip Kumar Mohapatra ◽  
Philip James Camp ◽  
John Philip
Keyword(s):  
Magnetic Field ◽  
Particle Size ◽  
Light Scattering ◽  
Optical Microscopy ◽  
Brownian Dynamics ◽  
Phase Contrast ◽  
Superparamagnetic Nanoparticles ◽  
Magnetic Nanofluids ◽  
Dynamics Simulations ◽  
Brownian Dynamics Simulations

We probe the influence of particle size polydispersity on field-induced structures and structural transitions in magnetic fluids (ferrofluids) using phase contrast optical microscopy, light scattering and Brownian dynamics simulations. Three...

scholarly journals Hard discs under steady shear: comparison of Brownian dynamics simulations and mode coupling theory

2009 ◽  
Vol 367 (1909) ◽  
pp. 5033-5050 ◽  
Author(s):  
Oliver Henrich ◽  
Fabian Weysser ◽  
Michael E. Cates ◽  
Matthias Fuchs
Keyword(s):  
Brownian Dynamics ◽  
Mode Coupling ◽  
Transition Density ◽  
Two Dimensions ◽  
Coupling Theory ◽  
Mode Coupling Theory ◽  
Stationary Structure ◽  
Homogeneous Shear Flow ◽  
Dynamics Simulations ◽  
Brownian Dynamics Simulations

Brownian dynamics simulations of bidisperse hard discs moving in two dimensions in a given steady and homogeneous shear flow are presented close to and above the glass transition density. The stationary structure functions and stresses of shear-melted glass are compared quantitatively to parameter-free numerical calculations of monodisperse hard discs using mode coupling theory within the integration through transients framework. Theory qualitatively explains the properties of the yielding glass but quantitatively overestimates the shear-driven stresses and structural anisotropies.

Sign in / Sign up

Export Citation Format

Share Document