Search results for "Viscosity."

Amorphous silica between confining walls and under shear: a computer simulation study

2002

Molecular dynamics computer simulations are used to investigate a silica melt confined between walls at equilibrium and in a steady-state Poisseuille flow. The walls consist of point particles forming a rigid face-centered cubic lattice and the interaction of the walls with the melt atoms is modelled such that the wall particles have only a weak bonding to those in the melt, i.e. much weaker than the covalent bonding of a Si-O unit. We observe a pronounced layering of the melt near the walls. This layering, as seen in the total density profile, has a very irregular character which can be attributed to a preferred orientational ordering of SiO4 tetrahedra near the wall. On intermediate lengt…

Imbibition of Femtoliter-Scale DNA-Rich Aqueous Droplets into Porous Nylon Substrates by Molecular Printing

2019

This work presents the first reported imbibition mechanism of femtoliter (fL)-scale droplets produced by microchannel cantilever spotting (μCS) of DNA molecular inks into porous substrates (hydrophilic nylon). Differently from macroscopic or picoliter droplets, the downscaling to the fL-size leads to an imbibition process controlled by the subtle interplay of evaporation, spreading, viscosity, and capillarity, with gravitational forces being quasi-negligible. In particular, the minimization of droplet evaporation, surface tension, and viscosity allows for a reproducible droplet imbibition process. The dwell time on the nylon surface permits further tuning of the droplet lateral size, in acc…

Visual indicator for the detection of end-of-life criterion for composite high pressure vessels for hydrogen storage

2012

International audience; A model to predict the accumulation of fibre breaks in advanced composites, that takes into account all physical phenomena implicated in fibre failure (i.e. the random nature, stress transfer due to breaks, fibre debonding and viscosity of the matrix) shows clearly that the failure of a unidirectional composite structure results in the formation of random fibre breaks which at higher loads coalesce into clusters of broken fibres. This stage of development is followed almost immediately by failure. This has direct application to filament wound pressure vessels of the type used to store hydrogen under high pressure. A novel, cost effective, method of revealing developi…

2015

We develop a model for the rheology of a three-phase suspension of bubbles and particles in a Newtonian liquid undergoing steady flow. We adopt an ‘effective-medium’ approach in which the bubbly liquid is treated as a continuous medium which suspends the particles. The resulting three-phase model combines separate two-phase models for bubble suspension rheology and particle suspension rheology, which are taken from the literature. The model is validated against new experimental data for three-phase suspensions of bubbles and spherical particles, collected in the low bubble capillary number regime. Good agreement is found across the experimental range of particle volume fraction ( 0 ≤ ϕ p ≲…

Photoresponsive anisotropic and isotropic gels of semicarbazide-azobenzene organogelators: the use of magnetic polymer colloids to detect gel-sol tra…

2020

Photoinduced gel-sol transformation of semicarbazide-azobenzene-based organogels containing entrapped organic solvents (isotropic gel) and liquid-crystalline material (anisotropic gel) has been studied. Thin films (4 µm) of gel materials were used to study the gel-sol transformation, as thicker films possess high absorbance due to the relatively high concentration of the gelator molecules. Photoinduced trans-cis isomerization of the azobenzene units causes destruction of the gel structure, and the consequent change in viscosity has been investigated employing magnetic polymer colloids. In the gel state the movement of the colloids is restricted due to their entrapment within the gel fibers …

Comparative evaluation of the swelling and degrees of cross-linking in three organic gel packings for SEC through some geometric parameters.

2003

Abstract The size exclusion chromatographic (SEC) behavior of five solvent/polymer systems in three organic column packings based on polystyrene/divinylbenzene (PS/DVB) copolymer, TSK-Gel H HR , μ-styragel and TSK-Gel H XL , has been compared. All the packings offer similar characteristics (pore size, particle size and efficiency) but some differences have been found when eluting the same systems. The different elution behavior observed in both polymeric gels has been analyzed in terms of their swelling and cross-linking degrees and of the fractal parameters. From the Universal Calibration plots, values of the chromatographic partition coefficient, K p , have been obtained and using some eq…

Influence of short-term aging on mechanical properties and morphology of polymer-modified bitumen with recycled plastics from waste materials

2020

Polymer-modified bitumen (PMB) is bitumen that has been specifically engineered with polymer for providing enhanced performance in service. The aging of bitumen is a main aspect that is able to affect its final performance: during the production phase in a hot mix plant, all the binders experience short-term aging due to the high processing temperature. The same is true during the production of the modified binder, when the polymer is dispersed at high temperature in the bitumen mass. This paper aims at studying the effect of short-term aging when using different types of modifiers such as recycled polymers obtained from waste materials. A 50/70 penetration-grade bitumen has been modified, …

First and second viscosity measurements in superfluid 3He-B

1996

By means of diaphragm-driven flow experiments in 3He-B in a thin slab geometry, we have measured the first and second viscosities, η and 3 at pressures of 0, 5, 10 and 29.3 bar. Our measurement of 3 has better established theoretical foundations than previous measurements and also extends to higher pressures. 3 and η were deduced from the frequency dependence of the flow dissipation determined from bandwidth measurements for several normal modes of the diaphragm; a first order slip correction was used in the determination of η. Near Tc, 3 α (1 - T/Tc)-1/2 in accordance with theoretical predictions but below T/Tc ~ 0.6 we observe a rapid drop in 3 signifying a departure from the hydrodynamic…

Molecular Dynamics Simulations

2003

A tutorial introduction to the technique of Molecular Dynamics (MD) is given, and some characteristic examples of applications are described. The purpose and scope of these simulations and the relation to other simulation methods is discussed, and the basic MD algorithms are described. The sampling of intensive variables (temperature T, pressure p) in runs carried out in the microcanonical (NVE) ensemble (N= particle number, V = volume, E = energy) is discussed, as well as the realization of other ensembles (e.g. the NVT ensemble). For a typical application example, molten SiO2, the estimation of various transport coefficients (self-diffusion constants, viscosity, thermal conductivity) is d…

Effect of hydroxyapatite concentration and size on morpho-mechanical properties of PLA-based randomly oriented and aligned electrospun nanofibrous ma…

2019

The growing demand for nanofibrous biocomposites able to provide peculiar properties requires systematic investigations of processing-structure-property relationships. Understanding the morpho-mechanical properties of an electrospun scaffold as a function of the filler features and mat microstructure can aid in designing these systems. In this work, the reinforcing effect of micrometric and nanometric hydroxyapatite particles in polylactic acid-based electrospun scaffold presenting random and aligned fibers orientation, was evaluated. The particles incorporation was investigated trough Fourier transform infrared spectroscopy in attenuated total reflectance. The morphology of the nanofibers …